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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