6
Working with Laboratory Equipment

   

6.A INTRODUCTION

 

109

   

6.B WORKING WITH WATER-COOLED EQUIPMENT

 

109

   

6.C WORKING WITH ELECTRICALLY POWERED LABORATORY EQUIPMENT

 

109

   

6.C.1 General Principles

 

109

   

6.C.1.1 Outlet Receptacles

 

109

   

6.C.1.2 Wiring

 

110

   

6.C.1.3 General Precautions for Working with Electrical Equipment

 

110

   

6.C.1.4 Personal Safety Techniques for Use with Electrical Equipment

 

112

   

6.C.1.5 Additional Safety Techniques for Equipment Using High Current or High Voltage

 

112

   

6.C.2 Vacuum Pumps

 

112

   

6.C.3 Refrigerators and Freezers

 

113

   

6.C.4 Stirring and Mixing Devices

 

114

   

6.C.5 Heating Devices

 

114

   

6.C.5.1 Ovens

 

116

   

6.C.5.2 Hot Plates

 

116

   

6.C.5.3 Heating Mantles

 

116

   

6.C.5.4 Oil, Salt, and Sand Baths

 

117

   

6.C.5.5 Hot Air Baths and Tube Furnaces

 

117

   

6.C.5.6 Heat Guns

 

118

   

6.C.5.7 Microwave Ovens

 

118

   

6.C.6 Ultrasonicators, Centrifuges, and Other Electrical Equipment

 

118

   

6.C.6.1 Ultrasonicators

 

118

   

6.C.6.2 Centrifuges

 

119

   

6.C.6.3 Electrical Instruments

 

119

   

6.C.7 Electromagnetic Radiation Hazards

 

119

   

6.C.7.1 Visible, Ultraviolet, and Infrared Laser Light Sources

 

119

   

6.C.7.2 Radio-frequency and Microwave Sources

 

119

   

6.C.7.3 X-rays, E-beams, and Sealed Sources

 

119

   

6.C.7.4 Miscellaneous Physical Hazards Presented by Electrically Powered Equipment

 

120

   

6.C.7.4.1 Magnetic Fields

 

120

   

6.C.7.4.2 Rotating Equipment and Moving Parts

 

120

   

6.C.7.4.3 Cutting and Puncturing Tools

 

120

   

6.C.7.4.4 Noise Extremes

 

120

   

6.C.7.4.5 Slips, Trips, and Falls

 

120

   

6.C.7.4.6 Ergonomics and Lifting

 

121

   

6.D WORKING WITH COMPRESSED GASES

 

121

   

6.D.1 Compressed Gas Cylinders

 

121

   

6.D.1.1 Identification of Contents

 

121



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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 6 Working with Laboratory Equipment     6.A INTRODUCTION   109     6.B WORKING WITH WATER-COOLED EQUIPMENT   109     6.C WORKING WITH ELECTRICALLY POWERED LABORATORY EQUIPMENT   109     6.C.1 General Principles   109     6.C.1.1 Outlet Receptacles   109     6.C.1.2 Wiring   110     6.C.1.3 General Precautions for Working with Electrical Equipment   110     6.C.1.4 Personal Safety Techniques for Use with Electrical Equipment   112     6.C.1.5 Additional Safety Techniques for Equipment Using High Current or High Voltage   112     6.C.2 Vacuum Pumps   112     6.C.3 Refrigerators and Freezers   113     6.C.4 Stirring and Mixing Devices   114     6.C.5 Heating Devices   114     6.C.5.1 Ovens   116     6.C.5.2 Hot Plates   116     6.C.5.3 Heating Mantles   116     6.C.5.4 Oil, Salt, and Sand Baths   117     6.C.5.5 Hot Air Baths and Tube Furnaces   117     6.C.5.6 Heat Guns   118     6.C.5.7 Microwave Ovens   118     6.C.6 Ultrasonicators, Centrifuges, and Other Electrical Equipment   118     6.C.6.1 Ultrasonicators   118     6.C.6.2 Centrifuges   119     6.C.6.3 Electrical Instruments   119     6.C.7 Electromagnetic Radiation Hazards   119     6.C.7.1 Visible, Ultraviolet, and Infrared Laser Light Sources   119     6.C.7.2 Radio-frequency and Microwave Sources   119     6.C.7.3 X-rays, E-beams, and Sealed Sources   119     6.C.7.4 Miscellaneous Physical Hazards Presented by Electrically Powered Equipment   120     6.C.7.4.1 Magnetic Fields   120     6.C.7.4.2 Rotating Equipment and Moving Parts   120     6.C.7.4.3 Cutting and Puncturing Tools   120     6.C.7.4.4 Noise Extremes   120     6.C.7.4.5 Slips, Trips, and Falls   120     6.C.7.4.6 Ergonomics and Lifting   121     6.D WORKING WITH COMPRESSED GASES   121     6.D.1 Compressed Gas Cylinders   121     6.D.1.1 Identification of Contents   121

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals     6.D.1.2 Handling and Use   122     6.D.1.2.1 Preventing and Controlling Leaks   122     6.D.1.2.2 Pressure Regulators   123     6.D.1.2.3 Flammable Gases   123     6.D.1.2.4 Empty Cylinders   124     6.D.2 Other Equipment Used with Compressed Gases   124     6.D.2.1 Records, Inspection, and Testing   124     6.D.2.2 Assembly and Operation   124     6.D.2.2.1 Pressure-Relief Devices   125     6.D.2.2.2 Pressure Gauges   125     6.D.2.2.3 Glass Equipment   126     6.D.2.2.4 Plastic Equipment   126     6.D.2.2.5 Piping, Tubing, and Fittings   126     6.D.2.2.6 Teflon Tape Applications   126     6.E WORKING WITH HIGH/LOW PRESSURES AND TEMPERATURES   126     6.E.1 Pressure Vessels   126     6.E.1.1 Records, Inspection, and Testing   127     6.E.1.2 Pressure Reactions in Glass Equipment   127     6.E.2 Liquefied Gases and Cryogenic Liquids   128     6.E.2.1 Cold Traps and Cold Baths   129     6.E.2.2 Selection of Low-Temperature Equipment   129     6.E.2.3 Cryogenic Lines and Supercritical Fluids   130     6.E.3 Vacuum Work and Apparatus   130     6.E.3.1 Glass Vessels   130     6.E.3.2 Dewar Flasks   130     6.E.3.3 Desiccators   131     6.E.3.4 Rotary Evaporators   131     6.E.3.5 Assembly of Vacuum Apparatus   131     6.F USING PERSONAL PROTECTIVE, SAFETY, AND EMERGENCY EQUIPMENT   131     6.F.1 Personal Protective Equipment and Apparel   131     6.F.1.1 Personal Clothing   131     6.F.1.2 Foot Protection   132     6.F.1.3 Eye and Face Protection   132     6.F.1.4 Hand Protection   132     6.F.2 Safety and Emergency Equipment   133     6.F.2.1 Spill Control Kits and Cleanup   133     6.F.2.2 Safety Shields   133     6.F.2.3 Fire Safety Equipment   134     6.F.2.3.1 Fire Extinguishers   134     6.F.2.3.2 Heat and Smoke Detectors   134     6.F.2.3.3 Fire Hoses   134     6.F.2.3.4 Automatic Fire-Extinguishing Systems   135     6.F.2.4 Respiratory Protective Equipment   135     6.F.2.4.1 Types of Respirators   135     6.F.2.4.2 Procedures and Training   136     6.F.2.4.3 Inspections   136     6.F.2.5 Safety Showers and Eyewash Fountains   136     6.F.2.5.1 Safety Showers   136     6.F.2.5.2 Eyewash Fountains   136     6.F.2.6 Storage and Inspection of Emergency Equipment   137     6.G EMERGENCY PROCEDURES   137

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 6.A INTRODUCTION Proper use of laboratory equipment is required to work safely with hazardous chemicals. Maintenance and regular inspection of laboratory equipment are an essential part of this activity. Many of the accidents that occur in the laboratory can be attributed to improper use or maintenance of laboratory equipment. This chapter discusses prudent practices for handling the apparatus often used in laboratories. The most common equipment hazards in laboratories come from electrically powered devices, and these are followed by hazards with devices for work with compressed gases and high/low pressures and temperatures. Other physical hazards include electromagnetic radiation hazards from such equipment as lasers and radio-frequency generating devices. Seemingly ordinary hazards such as floods from water-cooled equipment, accidents with rotating equipment and machines or tools for cutting and drilling, noise extremes, slips, trips, and falls, lifting, and poor ergonomics probably account for the greatest frequency of laboratory accidents and injuries. 6.B WORKING WITH WATER-COOLED EQUIPMENT The use of cooling water in laboratory condensers and other equipment is common laboratory practice, but can create a flooding hazard. The most common source of the problem is disconnection of the tubing supplying the water to the condenser. Hoses can pop off under irregular flows when building water pressure fluctuates or can break when the hose material has deteriorated from long-term use. Floods also result when exit hoses jump out of the sink from a strong flow pulse or sink drains are blocked by an accumulation of extraneous material. Proper use of hose clamps and maintenance of the entire cooling system or alternate use of a portable cooling bath with suction feed can resolve such problems. Plastic locking disconnects can make it easy to disconnect water lines without having to unclamp and reclamp secured lines. Some quick disconnects also incorporate check valves, which when disconnected do not allow flow into or out of either half of the connection. This feature allows for disconnecting and reconnecting with minimal spillage of water. 6.C WORKING WITH ELECTRICALLY POWERED LABORATORY EQUIPMENT Electrically powered laboratory equipment is used routinely for laboratory operations requiring heating, cooling, agitation or mixing, and pumping. Electrically powered equipment found in the laboratory includes fluid and vacuum pumps, lasers, power supplies, both electrophoresis and electrochemical apparatus, x-ray equipment, stirrers, hot plates, heating mantles, and, more recently, microwave ovens and ultrasonicators. Attention must be paid to both the mechanical and the electrical hazards inherent in these devices. High voltage and high power requirements are increasingly prevalent; therefore prudent practices for handling these devices are increasingly necessary. Electric shock is the major electrical hazard. A relatively low current of 10 milliamperes (mA) poses some danger, and 80 to 100 mA can be fatal. In addition, if improperly used, electrical equipment can serve as an ignition source for flammable or explosive vapors. Most of the risks involved can be minimized by regular, proper maintenance and a clear understanding of the correct use of the device. 6.C.1 General Principles Particular caution must be exercised during installation, modification, and repair, as well as during use of the equipment. In order to ensure safe operation, all electrical equipment must be installed and maintained in accordance with the provisions of the National Electrical Code (NEC) of the National Fire Protection Association (NFPA, 1991a). Laboratory workers should also consult state and local codes and regulations, which may contain special provisions and be more stringent than the NEC and NFPA rules. All repair and calibration work on electrical equipment must be carried out by properly trained and qualified personnel. Before modification, installation, or even minor repairs of electrical equipment are carried out, the devices must be deenergized and all capacitors discharged safely. Furthermore, this deenergized and/or discharged condition must be verified before proceeding (note that OSHA Control of Hazardous Energy Standard (29 CFR 1910.147; Lock out/Tag out) applies). It is imperative that each person participating in any experiment involving the use of electrical equipment be aware of all applicable equipment safety issues and be briefed on any potential problems. Workers can significantly reduce hazards and dangerous behavior by following some basic principles and techniques: checking and rechecking outlet receptacles (section 6.C.1.1), making certain that wiring complies with national standards and recommendations (section 6.C.1.2), and reviewing general precautions (section 6.C.1.3) and personal safety techniques (section 6.C.1.4). 6.C.1.1 Outlet Receptacles All 110-volt (V) outlet receptacles in laboratories should be of the standard design that accepts a three-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals FIGURE 6.1 Standard design for a three-wire grounded outlet. prong plug and provides a ground connection. Two-prong receptacles should be replaced as soon as feasible, and a separate ground wire should be added so that each receptacle is wired as shown in Figure 6.1. The ground wire should be on top so that anything falling onto the plug will not fall onto either the hot or the neutral line. It is also possible to fit a receptacle with a ground fault circuit interrupter (GFCI), which disconnects the current if a ground fault is detected. GFCI devices are required by local electrical codes for outdoor receptacles and for selected laboratory receptacles located less than 6 feet (1.83 meters) from sinks if maintenance of a good ground connection is essential for safe operation. These devices differ in operation and purpose from fuses and circuit breakers, which are designed primarily to protect equipment and prevent electrical fires due to short circuits or other abnormally high current draw situations. Certain types of GFCIs can cause equipment shutdowns at unexpected and inappropriate times; hence, their selection and use need careful planning. Receptacles that provide electric power for operations in hoods should be located outside the hood. This location prevents the production of electrical sparks inside the hood when a device is plugged in or disconnected, and it also allows a laboratory worker to disconnect electrical devices from outside the hood in case of an accident. Cords should not dangle outside the hood in such a way that they can accidentally be pulled out of their receptacles or tripped over. Simple, inexpensive plastic retaining strips and ties can be used to route cords safely. For fume hoods with airfoils, the electrical cords should be routed under the bottom airfoil so that the sash can be closed completely. Most airfoils can be easily removed and replaced with a screwdriver. 6.C.1.2 Wiring Laboratory equipment plugged into a 110-V (or higher) receptacle should be fitted with a standard three-conductor line cord that provides an independent ground connection to the chassis of the apparatus (see Figure 6.2). All electrical equipment should be grounded unless it is "double-insulated." This type of equipment has a two-conductor line cord that meets national codes and standards. The use of two-pronged "cheaters" to connect equipment with three-prong grounded plugs to old-fashioned two-wire outlets should be prohibited. The use of extension cords should be limited to temporary (less than one day) setups, if they are permitted at all. A standard three-conductor extension cord of sufficient rating for the connected equipment with an independent ground connection should be used. Electrical cables should be installed properly, even if only for temporary use, and should be kept out of aisles and other traffic areas. Overhead racks and floor channel covers should be installed if wires must pass over or under walking areas. Signal and power cables should not be intermingled in cable trays or panels. Special care is needed when installing and placing water lines (used, for example, to cool such equipment as flash lamps for lasers) so that they do not leak or produce condensation, which can dampen power cables nearby. Equipment plugged into an electrical receptacle should include a fuse or other overload protection device to disconnect the circuit if the apparatus fails or is overloaded. This overload protection is particularly useful for equipment likely to be left on and unattended for a long time, such as variable autotransformers (e.g., Variacs and powerstats), vacuum pumps, drying ovens, stirring motors, and electronic instruments. Equipment that does not contain its own built-in overload protection should be modified to provide such protection or replaced with equipment that provides it. Overload protection does not protect the worker from electrocution, but it does reduce the risk of fire. 6.C.1.3 General Precautions for Working with Electrical Equipment Laboratory personnel should be certain that all electrical equipment is maintained well, properly located, and safely used. In order to do this, the following precautions should be reviewed and the necessary adjustments made prior to working in the laboratory: Insulate all electrical equipment properly. Visually inspect all electrical cords monthly, especially in any laboratory where flooding can occur. Keep in mind that rubber-covered cords can be eroded by organic solvents and by ozone (produced by ultraviolet lamps). Replace all frayed or damaged cords before any

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals FIGURE 6.2 Standard wiring convention for 110-V electric power to equipment. further use of the equipment is permitted. Replacement should be conducted by qualified personnel. Ensure the complete electrical isolation of electrical equipment and power supplies. Enclose all power supplies in a manner that makes accidental contact with power circuits impossible. In every experimental setup, including temporary ones, employ suitable barriers or enclosures to protect against accidental contact with electrical circuits. Equip motor-driven electrical equipment used in a laboratory where volatile flammable materials may be present (e.g., a hydrogenation room) with either nonsparking induction motors that meet Class 1, Division 2, Group C-D electrical standards (U.S. DOC, 1993) or air motors instead of series-wound motors that use carbon brushes, such as those generally used in vacuum pumps, mechanical shakers, stirring motors, magnetic stirrers, and rotary evaporators. Do not use variable autotransformers to control the speed of an induction motor because such operation will cause the motor to overheat and perhaps start a fire. Because series-wound motors cannot be modified to make them spark-free, do not use kitchen appliances (refrigerators, mixers, blenders, and so on) with such motors in laboratories where flammable materials may be present. When bringing ordinary electrical equipment such as vacuum cleaners and portable electric drills having series-wound motors into the laboratory for special purposes, take specific precautions to ensure that no flammable vapors are present before such equipment is used (see Chapter 5, section G). Locate electrical equipment so as to minimize the possibility of spills onto the equipment or flammable vapors carried into it. If water or any chemical is spilled on electrical equipment, shut off the power immediately at a main switch or circuit breaker and unplug the apparatus. Minimize the condensation that may enter electrical equipment if it is placed in a cold room or a large refrigerator. Cold rooms pose a particular risk in this respect because the atmosphere is frequently at a high relative humidity, and the potential for water condensation is significant. If electrical equipment must be placed in such areas, mount the equipment on a wall or vertical panel. This precaution will reduce, though not eliminate, the condensation problem. Condensation can also cause electrical equipment to overheat, smoke, or catch fire. In such a case, shut off the power to the equipment immediately at a main switch or circuit breaker and unplug the apparatus. To minimize the possibility of electrical shock, carefully ground the equipment using a suitable flooring material, and install ground-fault circuit interrupters (GFCIs). Always unplug equipment before undertaking any adjustments, modifications, or repairs (with the exception of certain instrument adjustments as indicated in section 6.C.7). When it is necessary to handle equipment that is plugged in, be certain hands are dry

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals and, if feasible, wear nonconductive gloves and shoes with insulated soles. Ensure that all workers know the location and operation of power shutoffs (i.e., main switches and circuit breaker boxes) for areas in which they work. Do not use equipment again until it has been cleaned and properly inspected. ACETONE SPILLED UNDER AN ELECTRONIC BALANCE Acetone spilled out of a reaction vessel during the addition of dry ice. It seeped underneath a nearby electronic balance and ignited. The balance was severely damaged, but the fire was extinguished before the reaction vessel broke. All laboratories should have access to a qualified technician who can make routine repairs to existing equipment and modifications to new or existing equipment so that it will meet acceptable standards for electrical safety. The National Fire Protection Association's National Electrical Code Handbook (NFPA, 1993) provides guidelines. 6.C.1.4 Personal Safety Techniques for Use with Electrical Equipment Each individual working with electrical equipment should be informed of basic precautionary steps that should be taken to ensure personal safety: Avoid contact with energized electrical circuits. Electrical equipment should be serviced only by qualified individuals. Before qualified individuals service electrical equipment in any way, disconnect the power source to avoid the danger of electric shock. Ensure that any capacitors are, in fact, discharged. Before reconnecting electrical equipment to its power source after servicing, check the equipment with a suitable tester, such as a multimeter, to ensure that it is properly grounded. Do not reenergize a circuit breaker until there is assurance that the short circuit that activated it has been corrected. Install ground-fault circuit interrupters (GCFIs) as required by code to protect users from electric shock, particularly if an electrical device is hand-held during a laboratory operation. If a person is in contact with a live electrical conductor, first disconnect the power source and then remove the person from the contact and administer first aid. 6.C.1.5 Additional Safety Techniques for Equipment Using High Current or High Voltage Unless laboratory personnel are specially trained to install or repair high-current or high-voltage equipment, such tasks should be reserved for trained electrical workers. The following reminders are included for qualified personnel. Always assume that a voltage potential exists within a device while servicing it, even if it is deenergized and disconnected from its power source. For example, a device may contain capacitors, which retain a potentially harmful electrical charge. If it is not awkward or otherwise unsafe to do so, try to work with only one hand while keeping the other hand at your side or in a pocket, away from all conducting materials. This precaution reduces the likelihood of accidents that result in current passing through the chest cavity. Avoid becoming grounded by staying at least 6 inches away from walls, water, and all metal materials including pipes. Use voltmeters and test equipment with ratings and leads sufficient to measure the highest potential voltage to be found inside the equipment being serviced. 6.C.2 Vacuum Pumps Distillations or concentration operations that involve significant quantities of volatile substances should normally be performed with the use of a facility vacuum system, a water aspirator, or a steam aspirator-each system protected by a suitable trapping device-rather than a mechanical vacuum pump. However, the distillation of less-volatile substances, removal of final traces of solvents, and some other operations that require pressures lower than those obtainable with a water aspirator are normally performed with a mechanical vacuum pump. The suction line from the system to the vacuum pump should be fitted with a cold trap to collect volatile substances from the system and to minimize the amount of material that enters the vacuum pump and dissolves in the pump oil. A cold trap should also be used with a water aspirator to minimize contamination of discharged water. The possibility that mercury will be swept into the pump as a result of a sudden loss of vacuum can be minimized by placing

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals a trap in the line to the pump. Vacuum pump oil contaminated with mercury must be treated as hazardous waste. (See Chapter 5, sections 5.C.11.8 and 5.D.) The output of each pump should be vented to an air exhaust system. This procedure is essential when the pump is being used to evacuate a system containing a volatile toxic or corrosive substance. Failure to observe this precaution would result in pumping any of the substance that is not trapped into the laboratory atmosphere. It is also recommended to scrub or absorb the gases exiting the pump. Even with these precautions, however, volatile toxic or corrosive substances may accumulate in the pump oil and, thus, be discharged into the laboratory atmosphere during future pump use. This hazard can be avoided by draining and replacing the pump oil when it becomes contaminated. The contaminated pump oil should be disposed of by following standard RCRA procedures for the safe disposal of toxic or corrosive substances. General-purpose laboratory vacuum pumps should have a record of use in order to prevent cross-contamination or reactive chemical incompatibility problems. Belt-driven mechanical pumps with exposed belts must have protective guards. Such guards are particularly important for pumps installed on portable carts or tops of benches where laboratory workers might accidentally entangle clothing or fingers in the moving belt, but they are not necessary for enclosed pumps. 6.C.3 Refrigerators and Freezers The potential hazards posed by laboratory refrigerators involve vapors from the contents, the possible presence of incompatible chemicals, and spillage. As general precautions, laboratory refrigerators should be placed against fire-resistant walls, should have heavy-duty cords, and preferably should be protected by their own circuit breaker. The contents of a laboratory refrigerator should be enclosed in unbreakable secondary containers. Because there is almost never a satisfactory arrangement for continuously venting the interior atmosphere of a refrigerator, any vapors escaping from vessels placed in one will accumulate in the refrigerated space and will gradually be absorbed into the surrounding insulation. Thus, the atmosphere in a refrigerator could contain an explosive mixture of air and the vapor of a flammable substance or a dangerously high concentration of the vapor of a toxic substance or both. The potential for exposure to toxic substances can be aggravated when a worker places his or her head inside a refrigerator while searching for a particular sample. The placement of potentially explosive (see Chapter 5, sections 5.C and 5.G) or highly toxic substances (see Chapter 5, sections 5.D and 5.E) in a laboratory refrigerator is strongly discouraged. If this precaution must be violated, then a clear, prominent warning sign should be placed on the outside of the refrigerator door. Storage of these types of materials in a refrigerator should be kept to a minimum and monitored regularly. As noted in Chapter 5, section 5.C, laboratory refrigerators and freezers should never be used to store food or beverages for human consumption. AMPOULE EXPLOSION IN A REFRIGERATOR The door to a refrigerator used for storage of chemicals in a laboratory was left open for 10 minutes while a researcher searched through chemicals. Suddenly, an ampoule stored in the door exploded, spraying the contents in all directions, including toward the researcher. Fortunately, only one other container was ruptured, and the researcher received only a cut on his face from flying glass. A review of the incident concluded that the ampoule had been sealed at a relatively low temperature. When the ampoule warmed up in the open door, pressure built up inside it, causing it to rupture. There should be no potential sources of electrical sparks on the inside of a laboratory refrigerator where volatile or flammable chemicals are stored. Only refrigerators that have been Underwriters-approved for flammable storage by the manufacturer should be used for this purpose. If this is not possible, all new or existing manual defrost refrigerators should be modified by removing the interior light and switch mounted on the door frame, if present, and moving the contacts of the thermostat controlling the fan and temperature outside the refrigerated compartment. Although a prominent sign warning against the storage of flammable substances can be permanently attached to the door of an unmodified refrigerator, this alternative is less desirable than modifying the equipment by removing any spark sources from the refrigerated compartment. "Frost-free" refrigerators are not suitable for laboratory use, owing to the problems associated with attempts to modify them. Many of these refrigerators have a drain tube or hole that carries water (and any flammable material present) to an area adjacent to the compressor and, thus, present

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals a spark hazard. The electric heaters used to defrost the freezing coils are also a potential spark hazard (see Chapter 5, section 5.G.1). To ensure its effective functioning, a freezer should be defrosted manually when ice builds up. Uncapped containers of chemicals should never be placed in a refrigerator. Caps should provide a vapor-tight seal to prevent a spill if the container is tipped over. Aluminum foil, corks, corks wrapped with aluminum foil, and glass stoppers usually do not meet these criteria, and, therefore, their use should be discouraged. The most satisfactory temporary seals are normally screw-caps lined with either a conical polyethylene insert or a Teflon insert. The best containers for samples that are to be stored for longer periods of time are sealed, nitrogen-filled glass ampoules. At a minimum, catch pans should be used for secondary containment. Careful labeling of samples placed in refrigerators and freezers with both the contents and the owner's name is essential. Water-soluble ink should not be used, and labels should be waterproof or covered with transparent tape. Storing samples with due consideration of chemical compatibility is important in these often small, crowded spaces. 6.C.4 Stirring and Mixing Devices The stirring and mixing devices commonly found in laboratories include stirring motors, magnetic stirrers, shakers, small pumps for fluids, and rotary evaporators for solvent removal. These devices are typically used in laboratory operations that are performed in a hood, and it is important that they be operated in a way that precludes the generation of electrical sparks. Furthermore, it is important that, in the event of an emergency, such devices can be turned on or off from a location outside the hood. Heating baths associated with these devices (e.g., baths for rotary evaporators) should also be spark-free and controllable from outside the hood. (See sections 6.C.1 and 6.C.5; also see Chapter 5, section 5.C.7.) Only spark-free induction motors should be used in power stirring and mixing devices or any other rotating equipment used for laboratory operations. Although the motors in most of the currently marketed stirring and mixing devices meet this criterion, their on-off switches and rheostat-type speed controls can produce an electrical spark any time they are adjusted, because they have exposed contacts. Many of the magnetic stirrers and rotary evaporators currently on the market have this disadvantage. An effective solution is to remove any switches located on the device and insert a switch in the cord near the plug end; because the electrical receptacle for the plug should be outside the hood, this modification ensures that the switch will also be outside the hood. The speed of an induction motor operating under a load should not be controlled by a variable autotransformer. Because stirring and mixing devices, especially stirring motors and magnetic stirrers, are often operated for fairly long periods without constant attention, the consequences of stirrer failure, electrical overload, or blockage of the motion of the stirring impeller should be considered. It is good practice to attach a stirring impeller to the shaft of the stirring motor by using lightweight rubber tubing. If the motion of the impeller becomes impeded, the rubber can twist away from the motor shaft. If this occurs, the motor will not stall. However, this practice does not always prevent binding the impeller. Hence, it is also desirable to fit unattended stirring motors with a suitable fuse or thermal-protection device. (Also see section 6.C.1.) 6.C.5 Heating Devices Perhaps the most common types of electrical equipment found in a laboratory are the devices used to supply the heat needed to effect a reaction or a separation. These include ovens, hot plates, heating mantles and tapes, oil baths, salt baths, sand baths, air baths, hot-tube furnaces, hot-air guns, and microwave ovens. The use of steam-heated devices rather than electrically heated devices is generally preferred whenever temperatures of 100 °C or less are required. Because they do not present shock or spark risks, they can be left unattended with assurance that their temperature will never exceed 100 °C. A number of general precautions need to be taken when working with heating devices in the laboratory. First, new or existing variable autotransformers should be wired (or rewired) as illustrated in Figure 6.3. The actual heating element in any laboratory heating device should be enclosed in a glass, ceramic, or insulated metal case in such a fashion as to prevent a laboratory worker or any metallic conductor from accidentally touching the wire carrying the electric current. This type of construction minimizes the risk of electric shock and of accidentally producing an electrical spark near a flammable liquid or vapor (see Chapter 5, section 5.G.1). It also diminishes the possibility that a flammable liquid or vapor will come into contact with any wire whose temperature may exceed its ignition temperature. If any heating device becomes so worn or damaged that its heating element is exposed, the device should be either discarded or repaired to correct the damage before it is used again. Because many household appliances (e.g., hot plates and space heaters) do not meet this criterion, they should not be used in a

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals FIGURE 6.3 Schematic diagram of properly wired variable autotransformers. laboratory. Resistance devices used to heat oil baths should not contain bare wires. Laboratory heating devices should be used with a variable autotransformer to control the input voltage by supplying some fraction of the total line voltage, typically 110 V, to the heating element of the device. If a variable autotransformer is not wired in this manner, the switch on it may or may not disconnect both wires of the output from the 110 V line when it is switched to the off position. Also, if this wiring scheme has not been followed, and especially if the grounded three-prong plug is not used, even when the potential difference between the two output lines is only 10 V, each output line may be at a relatively high voltage (e.g., 110 V and 100 V) with respect to an electrical ground. Because these potential hazards exist, whenever a worker uses a variable autotransformer whose wiring scheme is not known, it is prudent to assume that either of the output lines carries a potential of 110 V and is capable of delivering a lethal electric shock. The external cases of all variable autotransformers have perforations for cooling by ventilation, and some sparking may occur whenever the voltage adjustment knob is turned. Therefore, these devices should be located where water and other chemicals cannot be spilled onto them and where their movable contacts will not be exposed to flammable liquids or vapors. Variable autotransformers should be mounted on walls or vertical panels and outside of hoods; they should not simply be placed on laboratory benchtops. Because the electrical input lines, including lines from variable transformers, to almost all laboratory heating devices have a potential of 110 V with respect to any electrical ground, these lines should always be viewed both as potential shock hazards and as potential spark hazards. Thus, any connection from these lines to a heating device should be both mechanically and electrically secure and completely covered with insulating material. Alligator clips should not be used to connect a line cord from a variable autotransformer to a heating device, especially to an oil bath or an air bath, because such connections pose a shock hazard. They also may slip off, creating an electrical spark and, perhaps, contacting other metal parts to create an additional hazard. All connections should be made by using, preferably, a plug and receptacle combination, or wires with insulated terminals firmly secured to insulated binding posts. Whenever an electrical heating device is used, it is essential to use either a temperature controller or a temperature-sensing device that will turn off the electric power if the temperature of the heating device exceeds some preset limit. Similar control devices are available that will turn off the electric power if the flow of cooling water through a condenser is stopped owing to the loss of water pressure or loosening of the water supply hose to a condenser. Fail-safe devices, which can be either purchased or fabricated, can prevent the more serious problems of fires or explosions that may arise if the temperature of a reaction increases significantly because of a change in line voltage, the accidental loss of reaction solvent, or loss of cooling. Fail-safe devices should be used for stills employed to purify reaction solvents, because such stills are often left unattended for significant periods of time. (See section 6.C.1 for additional information.)

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 6.C.5.1 Ovens Electrically heated ovens are commonly used in the laboratory to remove water or other solvents from chemical samples and to dry laboratory glassware. Never use laboratory ovens for human food preparation. Laboratory ovens should be constructed such that their heating elements and their temperature controls are physically separated from their interior atmospheres. Small household ovens and similar heating devices usually do not meet these requirements and, consequently, should not be used in laboratories. With the exception of vacuum drying ovens, laboratory ovens rarely have a provision for preventing the discharge of the substances volatilized in them into the laboratory atmosphere. Thus, it should be assumed that these substances will escape into the laboratory atmosphere and may also be present in concentrations sufficient to form explosive mixtures with the air inside the oven (see Chapter 5, section 5.G). This hazard can be reduced by connecting the oven vent directly to an exhaust system. Ovens should not be used to dry any chemical sample that has even moderate volatility and might pose a hazard because of acute or chronic toxicity unless special precautions have been taken to ensure continuous venting of the atmosphere inside the oven. Thus, most organic compounds should not be dried in a conventional unvented laboratory oven. To avoid explosion, glassware that has been rinsed with an organic solvent should not be dried in an oven until it has been rinsed again with distilled water. Potentially explosive mixtures can be formed from volatile substances and the air inside an oven. Bimetallic strip thermometers are preferred for monitoring oven temperatures. Mercury thermometers should not be mounted through holes in the tops of ovens so that the bulb hangs into the oven. Should a mercury thermometer be broken in an oven of any type, the oven should be closed and turned off immediately, and it should remain closed until cool. All mercury should be removed from the cold oven with the use of appropriate cleaning equipment and procedures (see Chapter 5, section 5.C.11.8) in order to avoid mercury exposure. After removal of all visible mercury, the heated oven should be monitored in a fume hood until the mercury vapor concentration drops below the threshold limit value (TLV). 6.C.5.2 Hot Plates Laboratory hot plates are normally used when solutions are to be heated to 100 °C or above and the inherently safer steam baths cannot be used as the source of heat. As previously noted, only hot plates that have completely enclosed heating elements should be used in laboratories. Although almost all laboratory hot plates now sold meet this criterion, many older ones pose an electrical spark hazard arising from either the on-off switch located on the hot plate, the bimetallic thermostat used to regulate the temperature, or both. Normally, these two spark sources are both located in the lower part of the hot plate in a region where any heavier-than-air and possibly flammable vapors evolved from a boiling liquid on the hot plate would tend to accumulate. In principle, these spark hazards can be alleviated by enclosing all mechanical contacts in a sealed container or by using solid-state circuitry for switching and temperature control. However, in practice, such modifications are difficult to incorporate into many of the hot plates now in use. Laboratory workers should be warned of the spark hazard associated with these hot plates. Any newly purchased hot plates should be set up in a way that avoids electrical sparks. In addition to the spark hazard, old and corroded bimetallic thermostats in these devices can eventually fuse shut and deliver full, continuous current to a hot plate. This risk can be avoided by wiring a fusible coupling into the line inside the hot plate. If the device does overheat, then the coupling will melt and interrupt the current (see Section 6.C.1). On many brands of combined stirrer/hot plates, the controls for the stirrer and temperature control look alike. Care must be taken to distinguish their functions. A fire or explosion may occur if the temperature rather than the stirrer speed is increased inadvertently. 6.C.5.3 Heating Mantles Heating mantles are commonly used for heating round-bottomed flasks, reaction kettles, and related reaction vessels. These mantles enclose a heating element in a series of layers of fiberglass cloth. As long as the fiberglass coating is not worn or broken, and as long as no water or other chemicals are spilled into the mantle (see section 6.C.1), heating mantles pose no shock hazard. They are normally fitted with a male plug that fits into a female receptacle on an output line from a variable autotransformer. This plug combination provides a mechanically and electrically secure connection. Heating mantles should always be used with a variable autotransformer to control the input voltage. They must never be plugged directly into a 110-V line. Workers should be careful not to exceed the input voltage recommended by the mantle manufacturer. Higher voltages will cause it to overheat, melting the fiberglass insulation and exposing the bare heating element.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals Some heating mantles are constructed by encasing the fiberglass mantle in an outer metal case that provides physical protection against damage to the fiberglass. If such metal-enclosed mantles are used, it is good practice to ground the outer metal case either by using a grounded, three-conductor cord from the variable autotransformer or by securely affixing one end of a heavy, braided conductor to the mantle case and the other end to a known electrical ground. This practice protects the worker against an electric shock if the heating element inside the mantle shorts against the metal case. 6.C.5.4 Oil, Salt, and Sand Baths In the use of oil, salt, and sand baths, care must be taken to avoid spilling water and other volatile substances into the baths. Such an accident can splatter hot material over a wide area and cause serious injuries. Electrically heated oil baths are often used to heat small or irregularly shaped vessels or when a stable heat source that can be maintained at a constant temperature is desired. For temperatures below 200 °C, a saturated paraffin oil is often used; a silicone oil should be used for temperatures up to 300 °C. Care must be taken with hot oil baths not to generate smoke or have the oil burst into flames from overheating. An oil bath should always be monitored by using a thermometer or other thermal sensing device to ensure that its temperature does not exceed the flash point of the oil being used. For the same reason, oil baths left unattended should be fitted with thermal sensing devices that will turn off the electric power if the bath overheats. These baths should be heated by an enclosed heating element, such as a knife heater, a tubular immersion heater such as a Calrod®, or its equivalent. The input connection for this heating element should be a male plug that will fit a female receptacle from a variable autotransformer (e.g., Variac) output line. Alternatively, a temperature controller can be used to control the temperature of the bath precisely. Temperature controllers are now available that can provide a variety of heating and cooling options. Oil baths must be well mixed to ensure that there are no ''hot spots" around the elements that take the surrounding oil to unacceptable temperatures. This problem can be minimized by placing the thermoregulator fairly close to the heater. Heated oil should be contained in either a metal pan or a heavy-walled porcelain dish; a Pyrex dish or beaker can break and spill hot oil if struck accidentally with a hard object. The oil bath should be mounted carefully on a stable horizontal support such as a laboratory jack that can be THERMITE REACTION EXPLOSION An explosion injuring 27 people occurred when a thermite reaction was being demonstrated as part of a magic show at an engineering open house. The demonstration, which generated molten iron in a 2,500 to 3,000 °C reaction, was being carried out in a clay flowerpot above a beaker of water and sand to show the heat produced by the reaction when molten iron particles fall into water. Suddenly, the demonstration exploded, sending hot metal and water toward the audience. The most likely cause of the accident was thought to be a physical vapor explosion, which can occur when a very hot liquid comes into contact with a second liquid. In this case, the water may have turned to steam so rapidly that an explosion resulted. The injuries consisted of minor burns. raised or lowered easily without danger of the bath tipping over. It is also important that equipment always be clamped high enough above a hot plate or oil bath that if the reaction begins to overheat, the heater can be lowered immediately and replaced with a cooling bath without having to readjust the clamps holding the equipment setup. A bath should never be supported on an iron ring because of the greater likelihood of accidentally tipping the bath over. Secondary containment should be provided in the event of a spill of hot oil. Proper protective gloves should be worn when handling a hot bath. Molten salt baths, like hot oil baths, offer the advantages of good heat transfer, commonly have a higher operating range (e.g., 200 to 425 °C), and may have a high thermal stability (e.g., 540 °C). The reaction container used in a molten salt bath must be able to withstand a very rapid heat-up to a temperature above the melting point of the salt. Care must be taken to keep salt baths dry, because they are hygroscopic, a property that can cause hazardous popping and splattering if the absorbed water vaporizes during heat-up. 6.C.5.5 Hot Air Baths and Tube Furnaces Hot air baths can be useful heating devices. Nitrogen is preferred for reactions in which flammable materials are used. Electrically heated air baths are frequently used to heat small or irregularly shaped vessels. Because of their inherently low heat capacity, such baths normally must be heated considerably above the

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals the area. Any reaction of this type should be carried out in a hood and labeled with signs that indicate the contents of the reaction vessel and the explosion risk. Glass tubes with high-pressure sealers should be no more than three-quarters full. Appropriate precautions using the proper shielding must be taken for condensing materials and sealing tubes. Vacuum work can be carried out on a Schlenck line as long as proper technique is used. The sealed glass tubes can be placed either inside pieces of brass or iron pipe capped at one end with a pipe cap or in an autoclave containing some of the reaction solvent (to equalize the pressure inside and outside the glass tube). The tubes can be heated with steam or in a specially constructed, electrically heated ''sealed-tube" furnace that is controlled thermostatically and located such that the force of an explosion would be directed into a safe area. When the required heating has been completed, the sealed tube or bottle should be allowed to cool to room temperature. Sealed bottles and tubes of flammable materials should be wrapped with cloth toweling, placed behind a safety shield, and then cooled slowly, first in an ice bath and then in dry ice. After cooling, the clamps and rubber stoppers can be removed from the bottles prior to opening. Personal protective equipment and apparel, including shields, masks, coats, and gloves, should be used during tube-opening operations. It should be noted that NMR tubes are often thin-walled and should only be used for pressure reactions in a special high-pressure probe or in capillary devices. Newly fabricated or repaired glass equipment for pressure or vacuum work should be examined for flaws and strains under polarized light. Corks, rubber stoppers, and rubber or plastic tubing should never be relied on as relief devices for protection of glassware against excess pressure; a liquid seal, Bunsen tube, or equivalent positive relief device should be used. When glass pipe is used, only proper metal fittings should be used. 6.E.2 Liquefied Gases and Cryogenic Liquids Cryogenic liquids are materials with boiling points of less than -73 °C (-100 °F). Liquid nitrogen, helium, and argon, and slush mixtures of dry ice with isopropanol are the materials most commonly used in cold traps to condense volatile vapors from a system. In addition, oxygen, hydrogen, and helium are often used in the liquid state. The primary hazards of cryogenic liquids are fire or explosion, pressure buildup (either slowly or due to rapid conversion of the liquid to the gaseous state), embrittlement of structural materials, frostbite, and asphyxiation. The extreme cold of cryogenic liquids requires special care in their use. The vapor that boils off from a liquid can cause the same problems as the liquid itself. The fire or explosion hazard is obvious when gases such as oxygen, hydrogen, methane, and acetylene are used. Air enriched with oxygen can greatly increase the flammability of ordinary combustible materials and may even cause some noncombustible materials to burn readily (see Chapter 5, sections 5.G.4 and 5.G.5). Oxygen-saturated wood and asphalt have been known to literally explode when subjected to shock. Because oxygen has a higher boiling point (-183 °C) than nitrogen (-195 °C), helium (-269 °C), or hydrogen (-252.7 °C), it can be condensed out of the atmosphere during the use of these lower-boiling-point cryogenic liquids. With the use of liquid hydrogen particularly, conditions may develop for an explosion. (See Chapter 5, sections 5.F.3 and 5.G.2, for further discussion.) It is advisable to furnish all cylinders and equipment containing flammable or toxic liquefied gases (not vendor-owned) with a spring-loaded pressure-relief device (not a rupture disk) because of the magnitude of the potential risk that can result from activation of a non-resetting relief device. Commercial cylinders of liquefied gases are normally supplied only with a fusible-plug type of relief device, as permitted by DOT regulations. Pressurized containers that contain cryogenic material should be protected with multiple pressure-relief devices. Cryogenic liquids must be stored, shipped, and handled in containers that are designed for the pressures and temperatures to which they may be subjected. Materials that are pliable under normal conditions can become brittle at low temperatures. Dewar flasks, which are used for relatively small amounts of material, should have a dust cap over the outlet to prevent atmospheric moisture from condensing and plugging the neck of the tube. Special cylinders insulated and vacuum-jacketed with pressure-relief valves and rupture devices to protect the cylinder from pressure buildup are available in capacities of 100 to 200 liters (L). A special risk to personnel is skin or eye contact with the cryogenic liquid. Because these liquids are prone to splash in use owing to the large volume expansion ratio when the liquid warms up, eye protection, preferably a face shield, should be worn when handling liquefied gases and other cryogenic fluids. The transfer of liquefied gases from one container to another should not be attempted for the first time without the direct supervision and instruction of someone experienced in this operation. Transfers should be done very slowly to minimize boiling and splashing.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals Unprotected parts of the body should not be in contact with uninsulated vessels or pipes that contain cryogenic liquids because extremely cold material may bond firmly to the skin and tear flesh if separation or withdrawal is attempted. Even very brief skin contact with a cryogenic liquid can cause tissue damage similar to that of frostbite or thermal burns, and prolonged contact may result in blood clots that have potentially very serious consequences. Gloves must be impervious to the fluid being handled and loose enough to be tossed off easily. A potholder may be a desirable alternative. Objects that are in contact with cryogenic liquids should also be handled with tongs or potholders. The work area should be well ventilated. Virtually all liquid gases present the threat of poisoning, explosion, or, at a minimum, asphyxiation in a confined space. Major harmful consequences of the use of cryogenic inert gases, including asphyxiation, are due to boiling off of the liquid and pressure buildup, which can lead to violent rupture of the container or piping. In general, liquid hydrogen should not be transferred in an air atmosphere because oxygen from the air can condense in the liquid hydrogen, presenting a possible explosion risk. All precautions should be taken to keep liquid oxygen from organic materials; spills on oxidizable surfaces can be hazardous. Though nitrogen is inert, its liquefied form can be hazardous because of its cryogenic properties and because displacement of air oxygen in the vicinity can lead to asphyxiation followed by death with little warning. Rooms that contain appreciable quantities of liquid nitrogen (N2) should be fitted with oxygen meters and alarms. Liquid nitrogen should not be stored in a closed room because the oxygen content of the room can drop to unsafe levels. Cylinders and other pressure vessels used for the storage and handling of liquefied gases should not be filled to more than 80% of capacity, to protect against possible thermal expansion of the contents and bursting of the vessel by hydrostatic pressure. If the possibility exists that the temperature of the cylinder may increase to above 30°C, a lower percentage (e.g., 60%) of capacity should be the limit. 6.E.2.1 Cold Traps and Cold Baths Cold traps should be chosen that are large enough and cold enough to collect the condensable vapors in a vacuum system. Cold traps should be checked frequently to make sure they do not become plugged with frozen material. Cold traps in a reduced-pressure system should be taped or placed in a metal can filled with vermiculite. After completion of an operation in which a cold trap has been used, the system should be vented in a safe and environmentally acceptable way. Otherwise, pressure could build up, creating a possible explosion and sucking pump oil into the system. Cold traps under continuous use, such as those used to protect inert atmosphere dry boxes, should be cooled electrically and monitored by low-temperature probes. Appropriate gloves and a face shield should be used to avoid contact with the skin when using cold baths. Dry gloves should be used when handling dry ice. Lowering of the head into a dry ice chest is to be avoided because carbon dioxide is heavier than air and asphyxiation can result. The preferred liquids for dry ice cooling baths are isopropyl alcohol or glycols, and the dry ice should be added slowly to the liquid portion of the cooling bath to avoid foaming. The common practice of using acetone-dry ice as a coolant should be avoided. Dry ice and liquefied gases used in refrigerant baths should always be open to the atmosphere. They should never be used in closed systems, where they may develop uncontrolled and dangerously high pressures. Extreme caution should be exercised in using liquid nitrogen as a coolant for a cold trap. If such a system is opened while the cooling bath is still in contact with the trap, oxygen may condens from the atmosphere. The oxygen could then combine with any organic material in the trap to create a highly explosive mixture. Thus, a system that is connected to a liquid nitrogen trap should not be opened to the atmosphere until the trap has been removed. Also, if the system is closed after even a brief exposure to the atmosphere, some oxygen (or argon) may have already condensed. Then, when the liquid nitrogen bath is removed or when it evaporates, the condensed gases will vaporize, producing a pressure buildup and the potential for explosion. The same explosion hazard can be created if liquid nitrogen is used to cool a flammable mixture that is exposed to air. 6.E.2.2 Selection of Low-Temperature Equipment Equipment used at low temperatures should be selected carefully. Temperature can dramatically change characteristics of materials. For example, even the impact strength of ordinary carbon steel is greatly reduced at low temperatures, and failure can occur at points of weakness, such as notches or abrupt changes in the material of construction, in cold equipment. When combinations of materials are required, it is important that the temperature dependence of their volumes be considered so that leaks, ruptures, and glass fractures can be avoided. For example, O-rings that provide a good seal at room temperature may lose resilience and fail to function on chilled equipment.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals IMPROPER GLASSWARE IN A CRYOGENIC FLUID A thin-walled Pyrex NMR sample tube containing absorbed hydrocarbons on platinum on an alumina support, which had been sealed under vacuum and annealed, was placed in a dry ice and chloroform mixture in a Dewar flask in a hood with horizontal sliding sashes. The tube exploded after approximately one minute in the bath, apparently due to thermal shock. Although the Dewar was not damaged, the researcher suffered severely irritated eyes and had to be transported to the trauma center. The researcher had been wearing glasses and a laboratory coat as personal protection, and the hood sash had been slid to the side. Face shields, goggles, gloves, and acrylic shielding were available in the laboratory but had not been used. The 18% chromium/8% nickel stainless steels retain their impact resistance down to approximately -240 °C, the exact value depending heavily on special design considerations. The impact resistance of aluminum, copper, nickel, and many other nonferrous metals and alloys increases with decreasing temperatures. Special alloy steels should be used for liquids or gases containing hydrogen at temperatures greater than 200 °C or at pressures greater than 34.5 MPa (500 psi) because of the danger of weakening carbon steel equipment by hydrogen embrittlement. 6.E.2.3 Cryogenic Lines and Supercritical Fluids Liquid cryogen transfer lines should be designed so that liquid cannot be trapped in any nonvented part of the system. Experiments in supercritical fluids include high pressure and should be carried out with appropriate protective systems. 6.E.3 Vacuum Work and Apparatus Vacuum work can result in an implosion and the possible hazards of flying glass, spattering chemicals, and fire. All vacuum operations must be set up and operated with careful consideration of the potential risks. Although a vacuum distillation apparatus may appear to provide some of its own protection in the form of heating mantles and column insulation, this is not sufficient because an implosion could scatter hot, flammable liquid. An explosion shield and a face mask should be used to protect the worker, and the procedure should be carried out in a hood. Equipment at reduced pressure is especially prone to rapid pressure changes, which can create large pressure differences within the apparatus. Such conditions can push liquids into unwanted locations, sometimes with undesirable consequences. Water, solvents, and corrosive gases should not be allowed to be drawn into a building vacuum system. When the potential for such a problem exists, a water aspirator with a solvent collection device and a trap with a check valve installed between the water aspirator and the apparatus, to prevent water from being drawn back into the apparatus, should be used as the vacuum source. Mechanical vacuum pumps should be protected by cold traps, and their exhausts should be vented to an exhaust hood or to the outside of the building. If solvents or corrosive substances are inadvertently drawn into the pump, the oil should be changed before any further use. (Oil contaminated with solvents, mercury, corrosive substances, and so on, must be handled as hazardous waste.) It may be desirable to maintain a log of pump usage as a guide to length of use and potential contaminants in the pump oil. The belts and pulleys on vacuum pumps should be covered with guards. (See section 6.C.2 for a discussion of vacuum pumps.) 6.E.3.1 Glass Vessels Although glass vessels are frequently used in low-vacuum operations, evacuated glass vessels may collapse violently, either spontaneously from strain or from an accidental blow. Therefore, pressure and vacuum operations in glass vessels should be conducted behind adequate shielding. It is advisable to check for flaws such as star cracks, scratches, and etching marks each time a vacuum apparatus is used. Only round-bottomed or thick-walled (e.g., Pyrex) evacuated reaction vessels specifically designed for operations at reduced pressure should be used. Repaired glassware is subject to thermal shock and should be avoided. Thin-walled, Erlenmeyer, or round-bottomed flasks larger than 1 L should never be evacuated. 6.E.3.2 Dewar Flasks Dewar flasks are under high vacuum and can collapse as a result of thermal shock or a very slight mechanical shock. They should be shielded, either by a layer of fiber-reinforced friction tape or by enclosure in a wooden or metal container, to reduce the risk of flying glass in case of collapse. Metal Dewar flasks

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals IMPLODING DEWAR A researcher was about to prepare an ice trap in a Dewar to cool a stationary stainless steel receiver on a chemical reactor system. The researcher had positioned the Dewar on a laboratory jack stand and had raised the Dewar into position. The Dewar imploded, propelling glass shards toward the researcher, who fortunately was wearing prescription safety glasses and received only minor facial cuts. The researcher should have been wearing a full-length face shield and should have had a cover on the Dewar. should be used whenever there is a possibility of breakage. Styrofoam buckets with lids can be a safer form of short-term storage and conveyance of cryogenic liquids than glass vacuum Dewars. Although they do not insulate as well as Dewar flasks, they eliminate the danger of implosion. 6.E.3.3 Desiccators If a glass vacuum desiccator is used, it should be made of Pyrex or similar glass, completely enclosed in a shield or wrapped with friction tape in a grid pattern that leaves the contents visible and at the same time guards against flying glass should the vessel implode. Plastic (e.g., polycarbonate) desiccators reduce the risk of implosion and may be preferable, but should also be shielded while evacuated. Solid desiccants are preferred. An evacuated desiccator should never be carried or moved. Care should be taken in opening the valve to avoid a shock wave into the desiccator. 6.E.3.4 Rotary Evaporators Glass components of the rotary evaporator should be made of Pyrex or similar glass, completely enclosed in a shield to guard against flying glass should the components implode. Increase in rotation speed and application of vacuum to the flask whose solvent is to be evaporated should be gradual. 6.E.3.5 Assembly of Vacuum Apparatus Vacuum apparatus should be assembled so as to avoid strain. Joints must be assembled so as to allow various sections of the apparatus to be moved if necessary without transmitting strain to the necks of the flasks. Heavy apparatus should be supported from below as well as by the neck. The assembler should avoid putting pressure on a vacuum line. Failure to keep the pressure below 1 atmosphere could lead to the stopcocks popping out at high velocity or to an explosion of the glass apparatus. Such increased pressure could result from warming of the contents of the trap due to failure to maintain low temperatures. Vacuum apparatus should be placed well back onto the bench or into the hood where they will not be inadvertently hit. If the back of the vacuum setup faces the open laboratory, it should be protected with panels of suitably heavy transparent plastic to prevent injury to nearby workers from flying glass in case of explosion. 6.F USING PERSONAL PROTECTIVE, SAFETY, AND EMERGENCY EQUIPMENT As outlined in previous chapters, it is essential for each laboratory worker to be proactive to ensure the laboratory is a safe working environment. This attitude begins with wearing appropriate apparel and using proper eye, face, hand, and foot protection when working with hazardous chemicals. It is the responsibility of the institution to provide appropriate safety and emergency equipment for laboratory workers and for emergency personnel. (See also section 5.C.) 6.F.1 Personal Protective Equipment and Apparel 6.F.1.1 Personal Clothing Clothing that leaves large areas of skin exposed is inappropriate in laboratories where hazardous chemicals are in use. The worker's personal clothing should be fully covering. Appropriate laboratory coats should be worn, buttoned, with the sleeves rolled down. Laboratory coats should be fire-resistant. Those fabricated of polyester are not appropriate for glassblowing or work with flammable materials. Cotton coats are inexpensive and do not burn readily. Laboratory coats or laboratory aprons made of special materials are available for high-risk activities. Laboratory coats that have been used in the laboratory should be left there to minimize the possibility of spreading chemicals to public assembly, eating, or office areas, and they should be cleaned regularly. (For more information, see the OSHA Personal Protective Equipment Standard (29 CFR 1910.132) and the OSHA Laboratory Standard (29 CFR 1910.1450).) Unrestrained long hair and loose clothing such as neckties, baggy pants, and coats are inappropriate in a laboratory where hazardous chemicals are in use. Such items can catch fire, be dipped in chemicals, and

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals get caught in equipment. Similarly, rings, bracelets, watches, or other jewelry that could be damaged, trap chemicals close to the skin, come in contact with electrical sources, or get caught in machinery should not be worn. Leather clothing or accessories should not be worn in situations where chemicals could be absorbed in the leather and held close to the skin. Protective apparel should always be worn if there is a possibility that personal clothing could become contaminated with chemically hazardous material. Washable or disposable clothing worn for laboratory work with especially hazardous chemicals includes special laboratory coats and aprons, jumpsuits, special boots, shoe covers, and gauntlets, as well as splash suits. Protection from heat, moisture, cold, and/or radiation may be required in special situations. Among the factors to be considered in choosing protective apparel, in addition to the specific application, are resistance to physical hazards, flexibility and ease of movement, chemical and thermal resistance, and ease of cleaning or disposal. Although cotton is a good material for laboratory coats, it reacts rapidly with acids. Plastic or rubber aprons can provide good protection from corrosive liquids but can be inappropriate in the event of a fire. Plastic aprons can also accumulate static electricity, and so they should not be used around flammable solvents, explosives sensitive to electrostatic discharge, or materials that can be ignited by static discharge. Disposable garments provide only limited protection from vapor or gas penetration. Disposable garments that have been used when handling carcinogenic or other highly hazardous material should be removed without exposing any individual to toxic materials and disposed of as hazardous waste. (See Chapter 5, sections 5.C.2.5 and 5.C.2.6.) 6.F.1.2 Foot Protection Street shoes may not be appropriate in the laboratory, where both chemical and mechanical hazards may exist. Substantial shoes should be worn in areas where hazardous chemicals are in use or mechanical work is being done. Clogs, perforated shoes, sandals, and cloth shoes do not provide protection against spilled chemicals. In many cases, safety shoes are advisable. Shoe covers may be required for work with especially hazardous materials. Shoes with conductive soles are useful to prevent buildup of static charge, and insulated soles can protect against electrical shock. 6.F.1.3 Eye and Face Protection Safety glasses with side shields that conform to ANSI standard Z87.1-1989 should be required for work with hazardous chemicals. Ordinary prescription glasses with hardened lenses do not serve as safety glasses. Contact lenses can sometimes be worn safely if appropriate eye and face protection is also worn (see, however, section 5.C.2.1). Although safety glasses can provide satisfactory protection from injury from flying particles, they do not fit tightly against the face and offer little protection against splashes or sprays of chemicals. It is appropriate for a laboratory to provide impact goggles that include splash protection (splash goggles), full-face shields that also protect the throat, and specialized eye protection (i.e., protection against ultraviolet light or laser light). Splash goggles, which have splash-proof sides to fully protect the eyes, should be worn if there is a splash hazard in any operation involving hazardous chemicals. Impact protection goggles should be worn if there is a danger of flying particles, and full-face shields with safety glasses and side shields are needed for complete face and throat protection. When there is a possibility of liquid splashes, both a face shield and splash goggles should be worn; this is especially important for work with highly corrosive liquids. Full-face shields with throat protection and safety glasses with side shields should be used when handling explosive or highly hazardous chemicals. If work in the laboratory could involve exposure to lasers, ultraviolet light, infrared light, or intense visible light, specialized eye protection should be worn. It also is appropriate for a laboratory to provide visitor safety glasses and a sign indicating that eye protection is required in laboratories where hazardous chemicals are in use. 6.F.1.4 Hand Protection Gloves appropriate to the hazard should be used at all times. It is important that the hands and any skin that is likely to be exposed to hazardous chemicals receive special attention. Proper protective gloves should be worn when handling hazardous chemicals, toxic materials, materials of unknown toxicity, corrosive materials, rough or sharp-edged objects, and very hot or very cold objects. Before the gloves are used, it is important that they be inspected for discoloration, punctures, or tears. A defective or improper glove can itself be a serious hazard in handling hazardous chemicals. If chemicals do penetrate glove material, they could then be held in prolonged contact with the hand and cause more serious damage than in the absence of a proper glove. The degradation and permeation characteristics of the glove material selected must be appropriate for protection from the hazardous chemicals being handled. Glove selection guides (available from most man-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals ufacturers) should be consulted, with careful consideration given to the permeability of any material, particularly when working with organic solvents, which may be able to permeate or dissolve the glove materials. The thin latex "surgical" vinyl and nitryl gloves that are popular in many laboratories because of their composition and thin construction may not be appropriate for use with highly toxic chemicals or solvents. For example, because latex is readily permeated by carbon disulfide, a hand covered by a latex glove immersed in carbon disulfide would receive constant wetting by this toxic chemical, which would by then be absorbed through the skin. Gloves should be replaced immediately if they are contaminated or torn. The use of double gloves may be appropriate in situations involving chemicals of high or multiple hazards. Leather gloves are appropriate for handling broken glassware and inserting tubing into stoppers, where protection from chemicals is not needed. Insulated gloves should be used when working with very hot or very cold materials. With cryogenic fluids the gloves must be impervious to fluid, but loose enough to be tossed off easily. Absorbent gloves could freeze on the hand and intensify any exposure to liquefied gases. Turning up the cuffs on gloves can prevent liquids from running down the arms when hands are raised. Gloves should be decontaminated or washed appropriately before they are taken off and should be left in the work area and not be allowed to touch any uncontaminated objects in the laboratory or any other area. Gloves should be replaced periodically, depending on the frequency of use. Regular inspection of their serviceability is important. If they cannot be cleaned, contaminated gloves should be disposed of according to institutional procedures. Barrier creams and lotions can provide some skin protection but should never be a substitute for gloves, protective clothing, or other protective equipment. These creams should be used only to supplement the protection offered by personal equipment. 6.F.2 Safety and Emergency Equipment Safety equipment, including spill control kits, safety shields, fire safety equipment, respirators, safety showers and eyewash fountains, and emergency equipment should be available in well-marked, highly visible locations in all chemical laboratories. Fire alarm pull stations and telephones with emergency telephone numbers clearly indicated must be readily accessible. In addition to the standard items, there may also be a need for other safety devices. It is the responsibility of the laboratory supervisor to ensure proper training and provide supplementary equipment as needed. 6.F.2.1 Spill Control Kits and Cleanup In most cases, researchers are responsible for cleaning up their own spills. If a spill exceeds their ability or challenges their safety, they should leave the spill site and call the emergency telephone number for help. Emergency response spill cleanup personnel should be given all available information about the spill. A spill control kit should be on hand. A typical cleanup kit may be a container on wheels that can be moved to the location of the spill and may include such items as instructions; absorbent pads; a spill absorbent mixture for liquid spills; a polyethylene scoop for dispensing spill absorbent; mixing it with the spill, and picking up the mixture; thick polyethylene bags for deposit of the mixture; and tags and ties for labeling the bags. Any kit should be used in conjunction with the personal protective equipment needed for the chemical that is to be cleaned up. Before beginning an operation that could produce a spill, the worker should locate the specialized spill control kits for that operation. (Also see Chapter 5, section 5.C.11.5.) 6.F.2.2 Safety Shields Safety shields should be used for protection against possible explosions or splash hazards. Laboratory equipment should be shielded on all sides so that there is no line-of-sight exposure of personnel. The front sashes of conventional laboratory exhaust hoods can provide shielding. However, a portable shield should also be used when manipulations are performed, particularly with hoods that have vertical-rising doors rather than horizontal-sliding sashes. Portable shields can be used to protect against hazards of limited severity, such as small splashes, heat, and fires. A portable shield, however, provides no protection at the sides or back of the equipment, and many such shields not sufficiently weighted for forward protection may topple toward the worker when there is a blast. A fixed shield that completely surrounds the experimental apparatus can afford protection against minor blast damage. Polymethyl methacrylate, polycarbonate, polyvinyl chloride, and laminated safety plate glass are all satisfactory transparent shielding materials. Where combustion is possible, the shielding material should be nonflammable or slow burning; if it can withstand the working blast pressure, laminated safety plate glass may be the best material for such circumstances. When cost, transparency, high tensile strength, resistance to bending loads, impact strength, shatter resistance, and burning rate are considered, polymethyl methacrylate offers an excellent overall combination of shielding characteristics.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals Polycarbonate is much stronger and self-extinguishing after ignition but is readily attacked by organic solvents. 6.F.2.3 Fire Safety Equipment 6.F.2.3.1 Fire Extinguishers All chemical laboratories should have carbon dioxide and dry chemical fire extinguishers. Other types of extinguishers should be available if required for the work being done. The four types of extinguishers most commonly used are classified by the type of fire for which they are suitable, as listed below. It should be noted that multipurpose class A, B, and C extinguishers are available. Water extinguishers are effective against burning paper and trash (class A fires). These should not be used for extinguishing electrical, liquid, or metal fires. Carbon dioxide extinguishers are effective against burning liquids, such as hydrocarbons or paint, and electrical fires (class B and C fires). They are recommended for fires involving computer equipment, delicate instruments, and optical systems because they do not damage such equipment. They are less effective against paper and trash fires and must not be used against metal hydride or metal fires. Care must be taken in using these extinguishers, because the force of the compressed gas can spread burning combustibles such as papers and can tip over containers of flammable liquids. Dry powder extinguishers, which contain ammonium phosphate or sodium bicarbonate, are effective against burning liquids and electrical fires (class B and C fires). They are less effective against paper and trash or metal fires. They are not recommended for fires involving delicate instruments or optical systems because of the cleanup problem. Computer equipment may need to be replaced if exposed to sufficient amounts of the dry powders. These extinguishers are generally used where large quantities of solvent may be present. Met-L-X® extinguishers and others that have special granular formulations are effective against burning metal (class D fires). Included in this category are fires involving magnesium, lithium, sodium, and potassium; alloys of reactive metals; and metal hydrides, metal alkyls, and other organometallics. These extinguishers are less effective against paper and trash, liquid, or electrical fires. Every extinguisher should carry a label indicating what class or classes of fires it is effective against and the date last inspected. There are a number of other, more specialized types of extinguishers available for unusual fire hazard situations. Each laboratory worker should be responsible for knowing the location, operation, and limitations of the fire extinguishers in the work area. It is the responsibility of the laboratory supervisor to ensure that all workers are shown the locations of fire extinguishers and are trained in their use. After use, an extinguisher should be recharged or replaced by designated personnel. 6.F.2.3.2 Heat and Smoke Detectors Heat sensors and/or smoke detectors may be part of the building safety equipment. If designed into the fire alarm system, they may automatically sound an alarm and call the fire department, they may trigger an automatic extinguishing system, or they may only serve as a local alarm. Because laboratory operations may generate heat or vapors, the type and location of the detectors must be carefully evaluated in order to avoid frequent false alarms. 6.F.2.3.3 Fire Hoses Fire hoses are intended for use by trained firefighters against fires too large to be handled by extinguishers and are included as safety equipment in some structures. Water has a cooling action and is effective against fires involving paper, wood, rags, trash, and such (class A fires). Water should not be used directly on fires that involve live electrical equipment (class C fires) or chemicals such as alkali metals, metal hydrides, and metal alkyls that react vigorously with it (class D fires). Streams of water should not be used against fires that involve oils or other water-insoluble flammable liquids (class B fires). Water will not readily extinguish such fires. Rather, it can cause the fire to spread or float to adjacent areas. These possibilities are minimized by the use of a water fog. Water fogs are used extensively by the petroleum industry because of their fire-controlling and extinguishing properties. A fog can be used safely and effectively against fires that involve oil products, as well as those involving wood, rags, rubbish, and such. Because of the potential risks involved in using water around chemicals, laboratory workers should refrain from using fire hoses except in extreme emergencies. Otherwise, such use should be reserved for trained firefighters. Clothing fires can be extinguished by immediately dropping to the floor and rolling; how-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals ever, if a safety shower is immediately available, it should be used (as noted in section 6.F.2.5). 6.F.2.3.4 Automatic Fire-Extinguishing Systems In areas where fire potential and the risk of injury or damage are high, automatic fire-extinguishing systems are often used. These may be of the water sprinkler, foam, carbon dioxide, halon, or dry chemical type. If an automatic fire-extinguishing system is in place, laboratory workers should be informed of its presence and advised of any safety precautions required in connection with its use (e.g., evacuation before a carbon dioxide total-flood system is activated, to avoid asphyxiation). 6.F.2.4 Respiratory Protective Equipment The primary method for the protection of laboratory personnel from airborne contaminants should be to minimize the amount of such materials entering the laboratory air. When effective engineering controls are not possible, suitable respiratory protection should be used after proper training. Respiratory protection may be needed in carrying out an experimental procedure, in dispensing or handling hazardous chemicals, in responding to a chemical spill or release in cleanup decontamination, or in hazardous waste handling. Under Occupational Safety and Health Administration (OSHA) regulations, only equipment listed and approved by the Mine Safety and Health Administration (MSHA) and the National Institute for Occupational Safety and Health (NIOSH) may be used for respiratory protection. Also under the regulations, each site on which respiratory protective equipment is used must implement a respirator program (including training and medical certification) in compliance with OSHA's Respiratory Protection Standard (29 CFR 1910.134); see also ANSI standard Z88.2-1992, Practices for Respiratory Protection. 6.F.2.4.1 Types of Respirators Several types of nonemergency respirators are available for protection in atmospheres that are not immediately dangerous to life or health but could be detrimental after prolonged or repeated exposure. Other types of respirators are available for emergency or rescue work in hazardous atmospheres from which the wearer needs protection. In either case, additional protection may be required if the airborne contaminant is of a type that could be absorbed through or irritate the skin. For example, the possibility of eye or skin irritation may require the use of a full-body suit and a full-face mask rather than a half-face mask. For some chemicals the dose from skin absorption can exceed the dose from inhalation. The choice of the appropriate respirator to use in a given situation depends on the type of contaminant and its estimated or measured concentration, known exposure limits, and hazardous properties. The degree of protection afforded by the respirator varies with the type. Four main types of respirators are currently available: Chemical cartridge respirators can be used only for protection against particular individual (or classes of) vapors or gases as specified by the respirator manufacturer and cannot be used at concentrations of contaminants above that specified on the cartridge. Also, these respirators cannot be used if the oxygen content of the air is less than 19.5%, in atmospheres immediately dangerous to life, or for rescue or emergency work. These respirators function by trapping vapors and gases in a cartridge or canister that contains a sorbent material, with activated charcoal being the most common adsorbent. Because it is possible for significant breakthrough to occur at a fraction of the canister capacity, knowledge of the potential workplace exposure and length of time the respirator will be worn is important. It may be desirable to replace the cartridge after each use to ensure the maximum available exposure time for each new use. Difficulty in breathing or the detection of odors indicates plugged or exhausted filters or cartridges or concentrations of contaminants higher than the absorbing capacity of the cartridge, and the user should immediately leave the area of contamination. Chemical cartridge respirators must be checked and cleaned on a regular basis. New and used cartridges must not be stored near chemicals because they are constantly filtering the air. Cartridges should be stored in sealed containers to prevent chemical contamination. Respirators must fit snugly on the face to be effective. Failure to achieve a good face-to-face piece seal (for example, because of glasses or facial hair) can permit contaminated air to bypass the filter and create a dangerous situation for the user. Respirators requiring a face-to-face piece seal should not be used by those with facial hair, for whom powered air-purifying or supplied-air respirators are at times appropriate. Tests for a proper fit must be conducted prior to selection of a respirator and verified before the user enters the area of contamination. Organic vapor cartridges cannot be used for vapors that are not readily detectable by their odor or other irritating effects or for vapors that will generate sub-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals stantial heat upon reaction with the sorbent materials in the cartridge. Dust, fume, and mist respirators can be used only for protection against particular, or certain classes of, dusts, fumes, and mists as specified by the manufacturer. The useful life of the filter depends on the concentration of contaminant encountered. Such particulate-removing respirators usually trap the particles in a filter composed of fibers; they are not 100% efficient in removing particles. Respirators of this type are generally disposable. Examples are surgical masks and 3M® toxic-dust and nuisance-dust masks. Some masks are NIOSH-approved for more specific purposes such as protection against simple or benign dust and fibrogenic dusts and asbestos. Particulate-removing respirators afford no protection against gases or vapors and may give the user a false sense of security. They are also subject to the limitations of fit. Supplied-air respirators supply fresh air to the face piece of the respirator at a pressure high enough to cause a slight buildup relative to atmospheric pressure. As a result, the supplied air flows outward from the mask, and contaminated air from the work environment cannot readily enter the mask. This characteristic renders face-to-face piece fit less important than with other types of respirators. Fit testing is, however, required before selection and use. Supplied-air respirators are effective protection against a wide range of air contaminants (gases, vapors, and particulates) and can be used where oxygen-deficient atmospheres are present. Where concentrations of air contaminants could be immediately dangerous to life, such respirators can be used provided (1) the protection factor of the respirator is not exceeded and (2) the provisions of OSHA's Respiratory Standard (which indicates the need for a safety harness and an escape system in case of compressor failure) are not violated. The air supply of this type of respirator must be kept free of contaminants (e.g., by use of oil filters and carbon monoxide absorbers). Most laboratory air is not suitable for use with these units. These units usually require the user to drag lengths of hose connected to the air supply, and they have a limited range. The self-contained breathing apparatus (SCBA) is the only type of respiratory protective equipment suitable for emergency or rescue work. Untrained personnel should not attempt to use them. 6.F.2.4.2 Procedures and Training Each area where respirators are used should have written information available that shows the limitations, fitting methods, and inspection and cleaning procedures for each type of respirator available. Personnel who may have occasion to use respirators in their work must be thoroughly trained, before initial use and annually thereafter, in the fit testing, use, limitations, and care of such equipment. Training should include demonstrations and practice in wearing, adjusting, and properly fitting the equipment. OSHA regulations require that a worker be medically certified before beginning work in an area where a respirator must be worn (OSHA Respiratory Standard, 29 CFR 1910.134(b)(10)). 6.F.2.4.3 Inspections Respirators for routine use should be inspected before each use by the user and periodically by the laboratory supervisor. Self-contained breathing apparatus should be inspected at least once a month and cleaned after each use. 6.F.2.5 Safety Showers and Eyewash Fountains 6.F.2.5.1 Safety Showers Safety showers should be available in areas where chemicals are handled. They should be used for immediate first aid treatment of chemical splashes and for extinguishing clothing fires. Every laboratory worker should know where the safety showers are located in the work area and should learn how to use them. Safety showers should be tested routinely to ensure that the valve is operable and to remove any debris in the system. The shower should be capable of drenching the subject immediately and should be large enough to accommodate more than one person if necessary. It should have a quick-opening valve requiring manual closing; a downward-pull delta bar is satisfactory if long enough, but chain pulls are not advisable because they can hit the user and be difficult to grasp in an emergency. It is preferable to have drains under safety showers to reduce the risks associated with the water. 6.F.2.5.2 Eyewash Fountains Eyewash fountains should be required in research or instructional laboratories if substances used there present an eye hazard or if unknown hazards may be encountered. An eyewash fountain should provide a soft stream or spray of aerated water for an extended period (15 minutes). These fountains should be located close to the safety showers so that, if necessary, the eyes can be washed while the body is showered.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 6.F.2.6 Storage and Inspection of Emergency Equipment It is often useful to establish a central location for storage of emergency equipment. Such a location should contain the following: self-contained breathing apparatus, blankets for covering the injured, stretchers (although it is generally best not to move a seriously injured person and to wait for qualified medical help to provide this service), first aid equipment (for unusual situations such as exposure to hydrofluoric acid or cyanide, where immediate first aid is required), and chemical spill cleanup kits and spill control equipment (e.g., spill pillows, booms, shoe covers, and a 55-gallon drum in which to collect sorbed material). (Also consult Chapter 5, sections 5.C.11.5 and 5.C.11.6.) Safety equipment should be inspected regularly (e.g., every 3 to 6 months) to ensure that it will function properly when needed. It is the responsibility of the laboratory supervisor or safety coordinator to establish a routine inspection system and to verify that inspection records are being kept. Inspections of emergency equipment should be performed as follows: Fire extinguishers should be inspected for broken seals, damage, and low gauge pressure (depending on type of extinguisher). Proper mounting of the extinguisher and its ready accessibility should also be checked. Some types of extinguishers must be weighed annually, and periodic hydrostatic testing may be required. Self-contained breathing apparatus should be checked at least once a month and after each use to determine whether proper air pressure is being maintained. The examiner should look for signs of deterioration or wear of rubber parts, harness, and hardware and make certain that the apparatus is clean and free of visible contamination. Safety showers and eyewash fountains should be examined visually and their mechanical function should be tested. They should be purged as necessary to remove particulate matter from the water line. 6.G EMERGENCY PROCEDURES The following emergency procedures are recommended in the event of a fire, explosion, spill, or medical or other laboratory accident. These procedures are intended to limit injuries and minimize damage if an accident should occur. Telephone numbers to call in emergencies should be posted clearly at all telephones in hazard areas. Have someone call for emergency help. State clearly where the accident has occurred and its nature. Ascertain the safety of the situation. Do not enter or reenter an unsafe area. Render assistance to the people involved and remove them from exposure to further injury. 4. Warn personnel in adjacent areas of any potential risks to their safety. Render immediate first aid; appropriate measures include washing under a safety shower, administration of CPR by trained personnel if heartbeat and/or breathing have stopped, and special first aid measures. Extinguish small fires by using a portable extinguisher. Turn off nearby equipment and remove combustible materials from the area. For larger fires, contact the appropriate fire department promptly. Provide emergency personnel with as much information as possible about the nature of the hazard. In case of medical emergency, laboratory personnel should remain calm and do only what is necessary to protect life. Summon medical help immediately. Do not move an injured person unless he or she is in danger of further harm. Keep the injured person warm. If feasible, designate one person to remain with the injured person. The injured person should be within sight, sound, or physical contact of that person at all times. If clothing is on fire and a safety shower is immediately available, douse the person with water; otherwise, move the person to the floor and roll him or her around to smother the flames. If harmful chemicals have been spilled on the body, remove them, usually by flooding the exposed area with sufficient running water from the safety shower, and immediately remove any contaminated clothing. If a chemical has splashed into the eye, immediately wash the eyeball and the inner surface of the eyelid with plenty of water for 15 minutes. An eyewash fountain should be used if available. Forcibly hold the eye open to wash thoroughly behind the eyelids. If possible, determine the identity of the chemical and inform the emergency medical personnel attending the injured person.

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