4
Management of Chemicals

   

4.A INTRODUCTION

 

64

   

4.B SOURCE REDUCTION

 

64

   

4.B.1 Importance of Minimizing Chemical Orders

 

64

   

4.B.2 Strategies to Minimize Hazardous Waste Generation

 

65

   

4.B.2.1 Microscale Work

 

65

   

4.B.2.2 Step-by-Step Planning for Minimization

 

66

   

4.B.2.3 Substitution of Materials

 

66

   

4.B.3 Strategies to Avoid Multihazardous Waste Generation

 

67

   

4.C ACQUISITION OF CHEMICALS

 

67

   

4.C.1 Ordering Chemicals

 

67

   

4.C.2 Receiving Chemicals

 

68

   

4.C.3 Responsibilities for Chemicals Being Shipped or Transported

 

68

   

4.D INVENTORY AND TRACKING OF CHEMICALS

 

69

   

4.D.1 General Considerations

 

69

   

4.D.2 Exchange or Transfer of Chemicals

 

70

   

4.D.3 Labeling Commercially Packaged Chemicals

 

71

   

4.D.4 Labeling Other Chemical Containers

 

71

   

4.D.5 Labeling Experimental Materials

 

71

   

4.D.6 Use of Inventory and Tracking Systems in Emergency Planning

 

72

   

4.E STORAGE OF CHEMICALS IN STOCKROOMS AND LABORATORIES

 

72

   

4.E.1 General Considerations

 

72

   

4.E.2 Containers and Equipment

 

73

   

4.E.3 Storing Flammable and Combustible Liquids

 

74

   

4.E.4 Storing Gas Cylinders

 

74

   

4.E.5 Storing Highly Reactive Substances

 

75

   

4.E.6 Storing Toxic Substances

 

76

   

4.F RECYCLING OF CHEMICALS, CONTAINERS, AND PACKAGING

 

76

   

4.F.1 General Considerations

 

76

   

4.F.2 Solvent Recycling

 

76

   

4.F.3 Mercury Recycling

 

76

   

4.F.4 Reclamation of Heavy Metals

 

77



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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 4 Management of Chemicals     4.A INTRODUCTION   64     4.B SOURCE REDUCTION   64     4.B.1 Importance of Minimizing Chemical Orders   64     4.B.2 Strategies to Minimize Hazardous Waste Generation   65     4.B.2.1 Microscale Work   65     4.B.2.2 Step-by-Step Planning for Minimization   66     4.B.2.3 Substitution of Materials   66     4.B.3 Strategies to Avoid Multihazardous Waste Generation   67     4.C ACQUISITION OF CHEMICALS   67     4.C.1 Ordering Chemicals   67     4.C.2 Receiving Chemicals   68     4.C.3 Responsibilities for Chemicals Being Shipped or Transported   68     4.D INVENTORY AND TRACKING OF CHEMICALS   69     4.D.1 General Considerations   69     4.D.2 Exchange or Transfer of Chemicals   70     4.D.3 Labeling Commercially Packaged Chemicals   71     4.D.4 Labeling Other Chemical Containers   71     4.D.5 Labeling Experimental Materials   71     4.D.6 Use of Inventory and Tracking Systems in Emergency Planning   72     4.E STORAGE OF CHEMICALS IN STOCKROOMS AND LABORATORIES   72     4.E.1 General Considerations   72     4.E.2 Containers and Equipment   73     4.E.3 Storing Flammable and Combustible Liquids   74     4.E.4 Storing Gas Cylinders   74     4.E.5 Storing Highly Reactive Substances   75     4.E.6 Storing Toxic Substances   76     4.F RECYCLING OF CHEMICALS, CONTAINERS, AND PACKAGING   76     4.F.1 General Considerations   76     4.F.2 Solvent Recycling   76     4.F.3 Mercury Recycling   76     4.F.4 Reclamation of Heavy Metals   77

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 4.A INTRODUCTION This chapter organizes the discussion of managing laboratory chemicals into five main topics: source reduction, acquisition, inventory and tracking, storage in stockrooms and laboratories, and recycling of chemicals and laboratory materials. As Chapter 1 makes clear, the concept of prudence in these areas requires knowledge of the hazards posed by laboratory chemicals and the formulation of reasonable measures to control and minimize the risks associated with their handling and disposal. It is not possible to eliminate risk altogether, but through informed risk assessment and careful risk management, laboratory safety can be greatly enhanced. Laboratory workers, laboratory supervisors, and individuals who handle chemicals all will find essential information in this chapter. Each of these people has an important role to play in a chemical's life cycle at an institution, and each one of them should be aware that the wise management of that life cycle can not only minimize risks to humans and to the environment, but also decrease costs. 4.B SOURCE REDUCTION Prudent management of chemicals in laboratories must begin long before the actual arrival of the chemicals. When experiments have been carefully planned, laboratory workers can be confident that they have chosen the procedures for working with chemicals that meet the following goals: to minimize quantities of chemicals to be used, to minimize disposal of hazardous materials, and to minimize risks. Strategies for achieving the first three goals generally also are effective in achieving a fourth: to minimize exposure of laboratory workers and storeroom and receiving personnel to hazardous materials. 4.B.1 Importance of Minimizing Chemical Orders In order to cut costs, manufacturing firms are increasingly asking for "just-in-time" delivery of raw materials. Laboratories might well borrow this strategy. A quantity of hazardous chemical not ordered is one to which workers are not exposed, for which appropriate storage need not be found, which need not be tracked in an inventory control system, and which will not end up requiring costly disposal when it becomes a waste. In acquiring a chemical, it is important to do a life cycle analysis. All costs associated with the progress of each chemical through its lifetime at an institution must be considered. The purchase cost is only the beginning; the handling costs, human as well as financial, and the disposal costs must be taken into account as well. Without close attention to this aspect of managing chemicals in laboratories, orders are not likely to be minimized and unused chemicals can become a significant fraction of the laboratory's hazardous waste. Institutions also need to minimize the amount of chemical accepted as a gift or as part of a research contract. More than one laboratory has been burdened with the cost of disposing of a donated chemical that was not needed. A "free" material can become a significant liability. The American Chemical Society's booklet Less Is Better: Laboratory Chemical Management for Waste Reduction (ACS, 1993) gives several reasons for ordering chemicals in smaller containers, even if that means using several containers of a material for a single experiment: The risk of breakage is substantially reduced for small package sizes. The risk of accident and exposure to the hazardous material is less when handling smaller containers. Storeroom space needs are reduced when only a single size is inventoried. Containers are emptied faster, resulting in less chance for decomposition of reactive compounds. The large "economy size" often dictates a need for other equipment, such as smaller transfer containers, funnels, pumps, and labels. Added labor to subdivide the larger quantities into smaller containers, as well as additional personal protective equipment for the hazards involved, also may be needed. If unused hazardous material must be disposed Donated material can easily become a liability. A chemical engineering researcher accepted a 55-gallon drum of an experimental diisocyanate as part of a research contract. The ensuing research project used less than 1 gallon of the material, and the grantor would not take the material back for disposal No commercial incinerator would handle the material in its bulk form. The remaining material had to be transferred to 1-liter containers and sent as Lab Packs for disposal, at a cost of $4,000 to $5,000.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals of, the disposal cost per container is less for smaller containers. Later in this chapter (section 4.D.2), the exchange or transfer of chemicals to other laboratory workers is discussed. The use of smaller containers increases the chance that chemicals to be transferred will still be in sealed containers, which increases the receiver's confidence that the chemicals are pure. 4.B.2 Strategies to Minimize Hazardous Waste Generation Experimental design and execution are central in strategies to minimize the generation of hazardous waste, just as they were in the section above. The design should evaluate all potential sources of hazardous waste expected from the proposed experiment and incorporate strategies to minimize those sources. Examples of such strategies include carrying out chemical reactions and other laboratory procedures on a smaller scale; considering the use to which a reaction product will be put and then making only the amount needed for that use; appreciating the price that may be paid for making and storing an unneeded material; thinking about minimization of material used in each step of an experiment; improving yields; using less solvent to rinse equipment, for example, by carrying out several rinses with small volumes of solvent, rather than using only one or two rinses with larger volumes; using more sensitive analytical equipment; substituting nonhazardous, or less hazardous, chemicals where possible by considering alternate synthetic routes and alternate procedures for working up reaction mixtures; recycling and reusing materials where possible, and coordinating laboratory work with co-workers who may be using some of the same chemicals (section 4.D.2); isolating nonhazardous waste from hazardous waste; and including in the experiment plan the reaction work-up steps that deactivate hazardous materials or reduce toxicity (see Chapter 7-examples include oxidation of carcinogens in situ or treating excess potassium metal with t-butyl alcohol). Clearly, some of these steps have become important only recently as a result of the changing requirements and economics of laboratory management. Three of these critical strategies are elaborated on below. 4.B.2.1 Microscale Work In microscale chemistry the amounts of materials used are reduced to 25 to 100 milligrams (mg) for solids and 100 to 200 microliters (µL) for liquids, compared to the usual 10 to 50 g for solids or 100 to 500 milliliters (mL) for liquids. Carrying out synthetic and analytical work on a small scale requires that smaller amounts of materials be ordered. Working with smaller amounts of materials can promote more attention to detail, which improves the quality of the science being done. The smaller scale also means that there will be less to recycle or dispose of from reaction work-up. Smaller quantities of items such as used filter papers, used filter cakes and filtrate from washings of the cakes, residues from distillation, and solvents to be redistilled will be produced. The glassware used in smaller-scale procedures is also generally not as easily broken as that required by procedures on a larger scale. Broken glassware contaminated with hazardous materials is itself a waste that must be disposed of. Microscale work also reduces the likelihood and severity of accidents resulting in personal exposure to hazardous chemicals. Fire hazards are also likely to be reduced. As an example of the benefits of microscale work, consider the typical Kjeldahl reaction, which uses mercury as a catalyst. The mercury waste produced by this procedure creates a difficult disposal problem. Converting to micro-Kjeldahl equipment and quantities reduces the waste by 90%, which could result in a reduction of several liters of waste per day in laboratories that routinely run Kjeldahl reactions. If 30,000 educational institutions that currently generate more than 4,000 metric tons of hazardous waste per year in the United States were to convert to microscale chemistry, 3,960 metric tons of that waste would be eliminated, at a savings of hundreds of millions of dollars per year. Many industrial research and development laboratories could achieve comparable financial and environmental savings. The committee recognizes that enormous quantities of hazardous waste can be minimized by converting to microscale chemistry with proportionate environmental and financial savings. Many tons of waste and millions of dollars would be saved by going to the microscale level. At the same time it must be recognized that multi-gram laboratory preparation is often required to provide sufficient material for further work. Precaution appropriate to the scale, as well as the inherent hazard, of a laboratory operation must be exercised.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 4.B.2.2 Step-by-Step Planning for Minimization Experiment planning in the new culture of laboratory safety should include minimization of the material used at each step of an experiment. Consider two simple examples: (1) Transferring a liquid reaction mixture or other solution from one flask to another container usually requires the use of a solvent to rinse out the flask. During this procedure, the worker should use the smallest amount of solvent possible that will enable a complete transfer. (2) Celite® is often used during filtrations to keep the pores of filter papers or filter frits from becoming clogged. When putting the Celite® in place, the worker should carefully determine the minimum amount needed to be effective. 4.B.2.3 Substitution of Materials To enhance safety and minimize the environmental consequences of an experiment, careful thought should be given to the materials to be used and the scale of an experiment. Traditionally, chemists have chosen reagents and materials for experiments to meet scientific criteria without always giving careful consideration to waste minimization or environmental objectives. In synthetic procedures, overall yield and purity of the desired product were usually regarded as the most important factors. Material substitution emerged as an important consideration in manufacturing process design because of the large quantities of chemicals involved. The following questions should now be considered when choosing a material to be used as a reagent or solvent in an experimental procedure: Can this material be replaced by one that will expose the experimenter, and others who handle it, to a lower order of potential hazard? Can this material be replaced by one that will reduce or eliminate the generation of hazardous waste and the consequent cost of waste disposal? The following examples illustrate applications of these principles to common laboratory procedures: A standard general chemistry experiment designed to study Beer's law involves the use of a considerable volume of a copper-ammonia complex. When this volume is multiplied by the number of students in a general chemistry class, a waste disposal problem is created, because a large quantity of copper should not be released directly into a sewage treatment system. The experiment has been modified to use an iron-salicylic acid complex instead, resulting in a waste product that can be disposed of via the sanitary sewer without causing environmental harm (although specific regulations must be consulted). Liquid scintillation counting of low-level radioactive samples using flammable solvent-based cocktails (e.g., based on xylene, toluene, or dioxane) requires precautions because of the flammability of the solvent and generates large volumes of waste, which must be disposed of by incineration. Substitution of nonflammable, water-miscible cocktails eliminates the fire hazard and generates aqueous waste, which can be disposed of via the sanitary sewer rather than by incineration in many localities. Implementation of this strategy at one major university resulted in a substantial reduction in the volume of flammable organic waste sent out for incineration. Acceptance of the new practice was achieved following demonstrations by key research groups that the new cocktails gave results comparable to those from the flammable solvent-based cocktails. Phosgene is a highly toxic gas used as a reagent in many organic transformations. Its use requires proper precautions to deal with the containment of the gas and the handling and disposal of cylinders. Commercially available substitutes such as diphosgene (trichloromethyl) chloroformate, a liquid, or triphosgene bis(trichloromethyl)carbonate, a low-melting solid, can often be substituted for phosgene by appropriate adjustment of experimental conditions or can be used to generate phosgene only on demand. Both chemicals are highly toxic themselves, but they offer a means to avoid the problems associated with handling a toxic gas. Many widely used reagents contain toxic heavy metals, such as chromium and mercury. Waste containing these materials cannot be incinerated and must be handled separately for disposal. Thus, substitution of other reagents for heavy metal reagents will almost always be beneficial with respect to hazard and waste minimization. Chromic acid cleaning solutions for glassware can be replaced by proprietary detergents used, if necessary, along with ultrasonic baths. Various chromium(VI) oxidants have been important in synthetic organic chemistry, but their use can often be avoided by the substitution of organic oxidants. The Swern oxidation of alcohols (oxalyl chloride/dimethyl sulfoxide) produces relatively innocuous by-products, which can be handled with other organic waste. Other oxidation reagents tailored to the specific needs of a given transformation are available. Fluorine and fluorinating reagents such as perchloryl fluoride are among the most demanding reagents to handle because of their high reactivity and toxicity. Accordingly, there has been considerable incentive to develop substitutes for these materials. One example is F-TEDA-BF4, or 1-chloromethyl-4fluoro-1,4-diazonia [2.2.2] bicycloctane bis(tetrafluoroborate). This reagent can be substituted for more hazardous reagents in many fluorination procedures.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals Organic solvents for liquid-liquid extraction or chromatography can often be replaced by other solvents with significant benefit. Benzene, once a widely used solvent, is now recognized as a human carcinogen and must be handled accordingly. Toluene can often serve as a satisfactory substitute. Diethyl ether is a flammable solvent whose handling must take into account its tendency to form explosive peroxides. Methyl t-butyl ether (MTBE) offers only slight advantages over diethyl ether with respect to flammability, but its greatly reduced tendency to form peroxides eliminates the need to monitor peroxide formation during handling and storage. The technology for handling supercritical fluids has developed rapidly in recent years. Supercritical carbon dioxide can replace organic solvents for high-performance chromatography and is beginning to find use as a reaction solvent. While supercritical solvents require specialized equipment for handling, they offer the potential benefit of large reductions in organic solvent waste. 4.B.3 Strategies to Avoid Multihazardous Waste Generation Because handling and disposal of multihazardous waste require special waste management, it is especially prudent to develop strategies to minimize its generation. Chapter 7, section 7.C.1.1, provides information on eliminating or minimizing the components of waste that are radioactive or biological hazards. The strategies discussed include substituting nonradioactive materials for radioactive materials, substituting radioisotopes having shorter decay times (e.g., using iodine-131, with a half-life of 8 days, instead of iodine-125, with a half-life of 60 days, in thyroid research), and carrying out procedures with smaller amounts of materials. 4.C ACQUISITION OF CHEMICALS 4.C.1 Ordering Chemicals Before purchasing a chemical, several questions should be asked: Is the material already available from another laboratory within the institution or from a surplus-chemical stockroom? If so, waste is reduced, and the purchase price is saved. The tendency to require the use of new chemicals because of their purity should be scrutinized and that requirement should be carefully justified to ensure that materials already on hand are used whenever possible. What is the minimum quantity that will suffice for the current use? Chemical purchases should not be determined by the cheaper unit price basis of large quantities, but rather by the amount needed for the experiment. The cost of disposing of the excess is likely to exceed any potential savings gained in a bulk purchase (i.e., in the present economic climate, the cost of getting rid of a chemical may exceed its acquisition cost). If a quantity smaller than the minimum offered by a supplier is needed, the supplier should be contacted and repackaging requested. Compressed gas cylinders, including lecture bottles, should normally be purchased only from suppliers who will accept return of empty cylinders. What is the maximum size container allowed in the areas where the material will be used and stored? Fire codes and institutional policies regulate quantities of certain chemicals, most notably flammables and combustibles. For these materials, a maximum allowable quantity for laboratory storage has been established (see also sections 4.E.3, 4.E.4, and 4.E.5). Can the chemical be managed safely when it arrives? Does it require special storage, such as in a dry box or freezer? Do receiving personnel need to be notified of the order and given special instructions for receipt? Will the equipment necessary to use the chemical be ready when it arrives? An effort should be made to order chemicals for just-in-time delivery, by purchasing all necessary materials from the same supplier with a request for delivery all together at the best time for performing an experiment. Is the chemical unstable? Inherently unstable materials may have very short storage times and should be purchased just before use to avoid losing a reagent and creating an unnecessary waste of material and time. Some materials may require express or overnight delivery and will not tolerate being held in transit over a weekend or holiday. Can the waste be managed satisfactorily? A chemical that will produce a new category of waste may cause a great deal of trouble for the waste management program. An appropriate waste disposal mechanism should be identified before the chemical is ordered. More detail on all of these questions should be reviewed as necessary to arrive at satisfactory answers. Only when these issues have been identified and resolved can ordering proceed. Authority to place orders for chemicals may be cen-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals tralized in one purchasing office or may be dispersed to varying degrees throughout the institution. The advent of highly computerized purchasing systems, and even on-line ordering, has made it attractive to allow ordering at the departmental or research group level. However, the ability to control ordering of certain types of materials through a central purchasing system (e.g., prohibiting flammables in containers over a certain size or ensuring appropriate licensing of radioactive material users) is almost completely lost as the purchasing function is decentralized. In these cases, other, creative ways of exercising control need to be found. One of the advantages of computerization of ordering is the information that can be retrieved from the chemical supplier. Some institutions have included in their annual contracts with suppliers a requirement to report on a monthly, quarterly, or annual basis the quantity of each type of chemical purchased and the location to which it was delivered. This information can be helpful in preparing the various annual reports on chemical use that may be required by federal, state, or local agencies. A purchase order for a chemical should include a request for a Material Safety Data Sheet (MSDS). However, many of the larger laboratory chemical suppliers have established a policy of sending each MSDS only once, when the chemical is first ordered. Subsequent orders of the same chemical may not be accompanied by the MSDS. Therefore, a central network of accessible MSDSs should be established if feasible. 4.C.2 Receiving Chemicals Chemicals arrive at institutions in a variety of ways, including U.S. mail, commercial package delivery, express mail services, and direct delivery from chemical warehouses. It is important to confine deliveries of chemicals to areas that are equipped to handle them, usually a loading dock, receiving room, or laboratory. Proper equipment for receipt of chemicals includes chains for temporary holding of cylinders and carts designed to safely move various types of chemical containers. Shelves, tables, or caged areas should be designated for packages to avoid damage by receiving room vehicles. Chemical deliveries should not normally be made to departmental offices because, in general, they are unlikely to be equipped to receive these packages. However, if delivery to such an office is the only option, a separate, undisturbed location, such as a table or shelf, should be identified for chemical deliveries, and the person ordering the material should be notified immediately upon its arrival. Receiving room, loading dock, and clerical personnel need to be trained adequately to recognize hazards that may be associated with chemicals coming into the facility. They need to know what is expected of them if a package is leaking or if there is a spill in the receiving facility, and they need to know whom to call for assistance when a problem develops. The Department of Transportation (DOT) requires training for anyone involved in the movement (including receiving) of hazardous materials (see Chapter 9, section 9.D.10). Transportation of chemicals within the facility, whether by internal staff or outside delivery personnel, must be done safely. Single boxes of chemicals, in their original packaging, can be hand carried to their destination if they are not too heavy to manage easily. Groups of packages or heavy packages should be transported by a cart that is stable, has straps or sides to contain packages securely, and has wheels large enough to negotiate uneven surfaces easily. Suitable carriers should be used when transporting individual containers of liquids. Cylinders of compressed gases should always be secured on specially designed carts and should never be dragged or rolled. The cap should always be securely in place. Whenever possible, chemicals and gas cylinders should be moved on ''freight-only" elevators. If outside delivery personnel do not handle materials according to the receiving facility's standards, immediate correction should be sought, or other carriers or suppliers should be used. Delivery criteria can be specified in the original purchase order. When packages are opened in the laboratory, laboratory personnel should verify that the container is intact and is labeled, at a minimum, with an accurate name on a well-adhered label. For unstable materials, and preferably for all materials, the date of receipt should be placed on the label. Labels placed by the manufacturer should not be obliterated or removed. New chemicals should be entered into the laboratory's inventory promptly and placed in the appropriate storage area. 4.C.3 Responsibilities for Chemicals Being Shipped or Transported The DOT regulates shipment of chemicals by a specific set of hazardous materials regulations (49 CFR 100-199). These regulations contain detailed instructions on how hazardous materials have to be identified, packaged, marked, labeled, documented, and placarded. Shipments not in compliance with the applicable regulations may not be offered or accepted for transportation. Since October 1, 1993, HM126F, a new, more stringent set of regulations on training for safe transportation of hazardous materials (49 CFR 172.700704), has been in effect. It is essential that all individuals who are preparing hazardous materials for shipment

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals communicate with their institution's transportation coordinators. Shipment of experimental materials is also discussed in Chapter 9, section 9.D.10. The use of personal vehicles, company or institutional vehicles (including airplanes), and customer vehicles for transporting regulated materials, which may be hazardous, is a serious concern. Most businesses and academic institutions forbid the use of privately owned personal vehicles, due to the serious insurance consequences if an accident occurs. Most individuals will find that their personal vehicle insurance does not cover them when they are transporting hazardous materials. Anyone who needs to transport regulated materials personally between buildings within an institution should walk. (Secondary containment, such as a rubber bucket, should always be used for carrying bottled chemicals.) 4.D INVENTORY AND TRACKING OF CHEMICALS 4.D.1 General Considerations Prudent management of chemicals in any laboratory is greatly facilitated by keeping an inventory of the chemicals stored. An inventory is a database that tabulates the chemicals in the laboratory, along with information essential for their proper management. Without an inventory of chemicals stored in a particular location, many important questions pertinent to prudent management of chemicals can be answered only by visually scanning container labels. A well-managed inventory system can promote economical use of chemicals by making it possible to determine immediately what chemicals are on hand. The scope of an inventory need not be limited to materials obtained from commercial sources, but can include chemicals synthesized in a laboratory that may be available for sharing. If the need for a chemical can be filled from a supply already on hand, the time and expense of procuring new material can be avoided. Information on chemicals that present particular storage or disposal problems can facilitate appropriate planning for their handling. While a detailed listing of hundreds of chemicals stored in a particular location may not be directly useful to emergency responders, it can be used to prepare a summary of the types of chemicals stored and the hazards that might be encountered. In larger organizations where chemicals are stored in multiple locations, the inventory system should include information on the storage location for each container of each chemical. If procedures for the facile updating of information on storage locations are developed, the system becomes a tracking system. Such a system can promote the sharing of chemicals originally purchased by different research groups or laboratories. The more that laboratories in an organization agree to share chemicals, the greater the likelihood that items unneeded in one location will find a use elsewhere. Tracking systems are more complex to establish than simple inventories and require more effort to maintain, but their favorable impact on the economics and efficiency of chemical use in a large organization will often justify their use. Each record in a chemical inventory database generally corresponds to a single container of a chemical rather than merely to the chemical itself. This approach allows for a more logical correspondence between the records in the database and the chemicals stored in the laboratory. The following data fields for each item are probably essential in any system: name as printed on the container, molecular formula, for further identification and to provide a simple means of searching, Chemical Abstract Service (CAS) registry number, for unambiguous identification of chemicals despite the use of different naming conventions, source, and size of container. In addition, the following information may be useful: hazard classification, as a guide to safe storage, handling, and disposal, date of acquisition, to ensure that unstable chemicals are not stored beyond their useful life, and storage location, in laboratories where multiple locations exist. In a chemical tracking system, the means by which the consumption of chemicals is tracked must be considered. The effort involved in maintaining data on the precise contents of each container must be weighed against the potential benefit such a system would provide. Many tracking systems ignore this information and record only the size of the container. A simple inventory system can be established by recording the above information for each container on index cards, which are then kept in an accessible location in some logical order, such as by molecular formula. The ease of searching such a card file is limited by its size and the order in which it is sorted. This type of system has obvious advantages in terms of simplicity and low cost, but it suffers several limitations. Listings of chemicals must be prepared manually, and the integrity of the database depends on how well the card file is maintained. For an inventory of more than a few hundred chemicals, a computer-based system offers many advantages. Many spreadsheet and database programs can

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals be used to maintain an effective chemical inventory system. The integrity of the inventory system can be enhanced by the ease of making backup copies of the database. Searches for desired chemicals can be carried out in a number of ways, depending on the capability of the software. The ability to sort the database, for example, by hazard classification, acquisition date, or other parameters, and to prepare lists of the results of such a sort, can contribute to efficiency in a variety of chemical management tasks. Section 4.C.1 above notes the prudence of establishing a central network of MSDSs. Including MSDSs and Laboratory Chemical Safety Summaries (LCSSs) (see Chapter 3 and Appendix B) in the inventory's database is highly desirable. The quality of MSDSs varies significantly from one manufacturer to another. LCSSs, which are targeted to the needs of the typical laboratory worker, are a useful supplement to the information provided by MSDSs. Having a fully capable chemical tracking system depends on careful selection of more sophisticated database software. Such a package should permit access from multiple terminals or networked computers and, most importantly, have a foolproof, efficient method for rapidly recording the physical transfer of a chemical from one location to another. Barcode labeling of chemical containers as they are received provides a means of rapid, error-free entry of information for a chemical tracking system. If reagent chemical suppliers were to adopt a system in which chemical containers were labeled with bar codes providing essential information on their products, the maintenance of chemical tracking systems would be greatly facilitated. Proprietary software packages for tracking of chemicals are available. The investment in hardware, software, and personnel to set up and maintain a chemical inventory tracking system is considerable, but it can pay significant dividends in terms of economical and prudent management of chemicals. As with any database, the utility of an inventory or chemical tracking system depends on the integrity of the information it contains. If an inventory system is used as a means of locating chemicals for use or sharing in the laboratory, even a moderate degree of inaccuracy will erode confidence in the system and discourage use. The need for high fidelity of data is greater for a tracking system, because laboratory workers will rely on it to save time locating chemicals using the system rather than physically searching. For these reasons, appropriate measures should be employed periodically to purge any inventory or tracking system of inaccurate data. A physical inventory of chemicals stored, verification of the data on each item, and reconciliation of differences can be performed annually. This procedure can coincide with an effort to identify unneeded, outdated, or deteriorated chemicals and to arrange for their disposal. The following guidelines for culling inventory may be helpful: Consider disposing of materials anticipated not to be needed within a reasonable period, say, 2 years. Stable, relatively nonhazardous substances may have indefinite shelf lives; a decision to retain them in storage should take into account their economic value, scarcity, availability, and storage costs. Make sure that deteriorating containers, or containers in which evidence of a chemical change in the contents is apparent (e.g., appearance of peroxide crystals in a bottle of an ether), are inspected and handled by someone experienced in the possible hazards inherent in such situations. Dispose of or recycle chemicals before the expiration date on the container. Replace deteriorating labels before information is obscured or lost. Because many odoriferous substances will make their presence known despite all efforts to contain them, aggressively purge such items from storage and inventory. Aggressively cull the inventory of chemicals that require storage at reduced temperature in environmental rooms or refrigerators. Because these chemicals may include air- and moisture-sensitive materials, they are especially prone to problems that can be exacerbated by the effects of condensation. Dispose of, or remove to storage, all hazardous chemicals at the completion of the laboratory supervisor's tenure or transfer to another laboratory. The institution's cleanup policy for departing laboratory researchers and students should be enforced strictly to avoid accumulation of expensive orphaned unknowns. Develop and enforce procedures relating to transfer or disposal of chemicals and other materials when decommissioning laboratories because of renovation or relocation. 4.D.2 Exchange or Transfer of Chemicals The exchange or transfer of chemicals between laboratories at an institution depends on the kind of inventory system and central stockroom facilities in place. Some institutions encourage laboratory workers to return materials to the central stockroom for redistribution to other workers. The containers may be sealed or open; a portion of the material may have been used. Materials from containers that have been opened are often of suffi-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals cient purity to be used "as is" in many procedures. If the purity is in doubt, the worker who returned the material should be consulted. The stockroom personnel can update the central inventory periodically to indicate which containers of which materials are available for this exchange or transfer. For an exchange program to be effective, all contributors to and users of the facility must reach a consensus on the standards to be followed concerning the labeling and purity of stored chemicals. A word of caution needs to be offered in regard to surplus-chemical stockrooms. It is essential that such a facility be managed with the same degree of control that is afforded a new-chemical storage area. The surplus-chemical stockroom must not be operated as a depository for any chemical that probably will not be wanted in the laboratory within a reasonable period (e.g., 2 to 3 years); such materials should be disposed of properly. Rooms that are used as general depositories of unwanted chemicals are likely to become "mini-Superfund" sites because of lack of control. Academic institutions should consider recycling common organic solvents from one research laboratory to another, or from research laboratories to teaching laboratories. For example, chromatography effluents such as toluene could be collected from research laboratories, distilled, and checked for purity before reuse. Such laboratory-to-laboratory exchange can be an effective alternative to a central surplus-chemical stockroom in organizations unwilling or unable to manage a central storeroom properly. In such a system, workers in the individual laboratory retain responsibility for the storage of unwanted chemicals but notify colleagues periodically of available materials. A chemical tracking system as described above can facilitate an exchange system greatly. If colleagues within the same laboratory are using the same hazardous material, particularly one that is susceptible to decomposition upon contact with air or water, they should try to coordinate the timing of their experiments. 4.D.3 Labeling Commercially Packaged Chemicals Commercially packaged chemical containers received from 1986 onward generally meet current labeling requirements. The label usually includes the name of the chemical and any necessary handling and hazard information. Inadequate labels on older containers should be updated to meet current standards. To avoid ambiguity about chemical names, many labels carry the CAS registry number as an unambiguous identifier. This information should be added to any label that does not include it. On receipt of a chemical, the manufacturer's label should be supplemented by the date received and possibly the name and location of the individual responsible for purchasing the chemical. If chemicals from commercial sources are repackaged into secondary containers, the new containers should be labeled with all essential information on the original container. Warning: Do not remove or deface any existing labels on incoming containers of chemicals and other materials. 4.D.4 Labeling Other Chemical Containers The contents of all chemical containers, including, but not limited to, beakers, flasks, reaction vessels, and process equipment, should be properly identified. The overriding goal of prudent practice in the identification of laboratory chemicals is to avoid orphaned containers of unknown materials that may be expensive or dangerous to dispose of. The labels should be understandable to laboratory workers, members of well-trained emergency response teams, and others. Labels or tags should be resistant to fading from aging, chemical exposure, temperature, humidity, and sunlight. Chemical identification and hazard warning labels on containers used for storing chemicals should include the following information: name, address, and telephone number of the chemical manufacturer, importer, or responsible party (including researcher), chemical identification and identity of hazard component(s), and appropriate hazard warnings. Containers in immediate use, such as beakers and flasks, should, at a minimum, be labeled with the name of the chemical contents. Labeled materials transferred from primary (labeled) containers to secondary containers (e.g., safety cans and squeeze bottles) should include chemical identification and synonyms, precautions, and first aid information. 4.D.5 Labeling Experimental Materials Labeling of all containers of experimental chemical materials is prudent. Because the properties of an experimental material are generally not completely known, its label cannot be expected to provide all necessary information to ensure safe handling. The most important information on the label of an experimental material is the name of the researcher responsible, as well as any other information, such as a laboratory notebook reference, that can readily lead to what is known about the material. For items that are to be stored and retained within a laboratory where the properties of materials are likely to be well understood, only the sample identification and/or name may

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals be needed. Samples that will be transferred outside the laboratory, or that may be handled by individuals not generally familiar with the type of material involved, should be labeled as completely as possible, including the name, address, and telephone number of the sender and recipient for samples in transit. In addition, samples that are sent to individuals at another institution must be accompanied by appropriate labeling and a Material Safety Data Sheet, according to OSHA's Hazard Communication Standard amendments and OSHA's Laboratory Standard "hazard identification" provision. When available, the following information should accompany experimental materials: Originator: give the name, location, and telephone number of the person to contact for safe handling information. Identification: include, at least, the laboratory notebook reference. Hazardous components: list primary components that are known to be hazardous. Potential hazards: indicate all the known or suspected potential hazards. Date: note the date that the material was placed in the container and labeled. Ship: indicate the name, location, and telephone number of the person to whom the material is being transferred. 4.D.6 Use of Inventory and Tracking Systems in Emergency Planning The most important assistance to have in an emergency is access to a researcher who is knowledgeable about the chemical(s) involved. In addition, an organization's emergency preparedness plan should include components on what to do in the event of a hazardous materials release. The information in the inventory and tracking systems and the ability of individuals to access and make use of it are essential to proper functioning of the plan in an emergency. The care taken in labeling chemicals is also extremely important. See Chapter 5, section 5.C.11, for a detailed discussion of what to do in laboratory emergencies. 4.E STORAGE OF CHEMICALS IN STOCKROOMS AND LABORATORIES The storage requirements and limitations for stockrooms and laboratories vary widely depending on level of expertise of the employees, level of safety features designed into the facility, location of the facility, nature of the chemical operations, accessibility of the stockroom, local and state regulations, insurance requirements, and building and fire codes. Many local, state, and federal regulations have specific requirements that affect the handling and storage of chemicals in laboratories and stockrooms. For example, radioactive materials, controlled substances (drugs), consumable alcohol, explosives, needles, hazardous waste, and so forth have requirements ranging from locked storage cabinets and controlled access to specified waste containers and "regulated" areas. Stringent requirements may also be placed on an institution by its insurance carriers. Of particular applicability are fire and building codes, which may be either local or statewide and which have become considerably more rigorous in the past several years. All of these specific requirements must be identified when designing procedures for laboratory and stockroom storage. Other elements to consider include the safety features designed into the facility, the location of the facility, and the nature of the chemical operations. 4.E.1 General Considerations In general, store materials and equipment in cabinets and on shelving provided for such storage. Avoid storing materials and equipment on top of cabinets. If you must place things there, however, maintain a clearance of at least 18 inches from the sprinkler heads to allow proper functioning of the sprinkler system. Do not store materials on top of high cabinets where they will be hard to see or reach. Avoid storing heavy materials up high. Keep exits, passageways, areas under tables or benches, and emergency equipment areas free of stored equipment and materials. Storing chemicals in stockrooms and laboratories requires consideration of a number of health and safety factors. In addition to the inventory control and storage area considerations as discussed above, proper use of containers and equipment is crucial (see section 4.E.2). In addition to the basic storage area guidelines above, these general guidelines should be followed when storing chemicals: Label all chemical containers appropriately. Place the user's name and the date received on all

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals TABLE 4.1 Related and Compatible Storage Groups Inorganic Family Nitric acid, other inorganic acids Metals, hydrides Sulfur, phosphorus, arsenic, phosphorus Halides, sulfates, sulfites, thiosulfates, pentoxide phosphates, halogens Organic Family Amides, nitrates (except ammonium nitrate) , nitrites, azides Acids, anhydrides, peracids Hydroxides, oxides, silicates, carbonates, carbon Alcohols, glycols, amines, amides, imines, imides Hydrocarbons, esters, aldehydes Sulfides, selenides, phosphides, carbides, nitrides Ethers, ketones,ketenes, halogenatedhydrocarbons, ethylene oxide Chlorates, perchlorates, perchloric acid, chlorites, hypochlorites, peroxides, hydrogen peroxide Epoxy compounds, isocyanates Peroxides, hydroperoxides, azides Arsenates, cyanides, cyanates Sulfides, polysulfides, sulfoxides, nitrites Borates, chromates, manganates, permanganates Phenols, cresols NOTE: Store flammables in a storage cabinet for flammable liquids or in safety cans. Separate chemicals into their organic and inorganic families and then related and compatible groups, as shown. Separation of chemical groups can be by different shelves within the same cabinet. Do NOT store chemicals alphabetically as a general group. This may result in incompatibles appearing together on a shelf. Rather, store alphabetically within compatible groups. This listing is only a suggested method of arranging chemical materials for storage and is not intended to be complete. purchased materials in order to facilitate inventory control of the materials. Provide a definite storage place for each chemical and return the chemical to that location after each use. Avoid storing chemicals on bench tops, except for those chemicals being used currently. Avoid storing chemicals in laboratory hoods, except for those chemicals being used currently. Store volatile toxics and odoriferous chemicals in a ventilated cabinet. Check with the institution's environmental health and safety officer. Provide ventilated storage near laboratory hoods. If a chemical does not require a ventilated cabinet, store it inside a closable cabinet or on a shelf that has a lip to prevent containers from sliding off in the event of a fire, serious accident, or earthquake. Do not expose stored chemicals to heat or direct sunlight. Observe all precautions regarding the storage of incompatible chemicals. Separate chemicals into compatible groups and store alphabetically within compatible groups. See Table 4.1 for one suggested method for arranging chemicals in this way. Store flammable liquids in approved flammable liquid storage cabinets. In seismically active regions, storage of chemicals requires additional consideration for the stability of shelving and containers. Shelving and other storage units should be secured. Shelving should contain a front-edge lip to prevent containers from falling. Ideally, containers of liquids should be placed on a metal or plastic tray that could hold the liquid if the container broke while on the shelf. All laboratories, not only those in seismically active regions, can benefit from these additional storage precautions. 4.E.2 Containers and Equipment Specific guidelines regarding containers and equipment to use in storing chemicals are as follows: Use corrosion-resistant storage trays or secondary containers to retain materials if the primary container breaks or leaks. Provide vented cabinets beneath laboratory hoods for storing hazardous materials. (This encour-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals ages the use of the hoods for transferring such materials.) Use chemical storage refrigerators only for storing chemicals. Label these refrigerators with the following signage: NO FOOD—CHEMICAL STORAGE ONLY Seal containers to minimize escape of corrosive, flammable, or toxic vapors. Label all materials in the refrigerator with contents, owner, date of acquisition or preparation, and nature of any potential hazard. Do not store flammable liquids in a refrigerator unless it is approved for such storage. Such refrigerators are designed not to spark inside the refrigerator. If refrigerated storage is needed inside a flammable-storage room, it is advisable to choose an explosion-proof refrigerator. 4.E.3 Storing Flammable and Combustible Liquids The National Fire Protection Association (NFPA) Standard 45 (NFPA, 1991d) limits the quantity of flammable and combustible liquids per 100 square feet of laboratory space. (Local regulations should also be consulted.) The quantity depends on these safety factors: construction of the laboratory, fire protection systems built into the laboratory, storage of flammable liquids in flammable liquid storage cabinets or safety cans, and type of laboratory (i.e., instructional or research and development). Many laboratories have a B (business) classification with sprinkler systems and have a flammable and combustible liquid storage limitation, as shown in Table 4.2. The container size for storing flammable and combustible liquids is limited both by NFPA Standards 30 and 45 and by OSHA. Limitations are based on the type of container and the flammability of the liquid, as shown in Table 4.3. The following precautions should be taken when storing flammable liquids: When possible, store quantities of flammable liquids greater than 1 L (approximately 1 quart, or 32 ounces) in safety cans. Refer to Table 4.3. Store combustible liquids either in their original (or other NFPA-and DOT-approved) containers or in safety cans. Refer to Table 4.3. 4.E.4 Storing Gas Cylinders The following precautions should be taken when storing compressed gas cylinders: Always label cylinders so you know their contents; do not depend on the manufacturer's color code. Securely strap or chain gas cylinders to a wall or bench top. In seismically active areas, it may be advisable to use more than one strap or chain. When cylinders are no longer in use, shut the valves, relieve the pressure in the gas regulators, remove the regulators, and cap the cylinders. Segregate gas cylinder storage from the storage of other chemicals. Keep incompatible classes of gases stored separately. Keep flammables from reactives, which include oxidizers and corrosives. Segregate empty cylinders from full cylinders. Keep in mind the physical state—compressed, cryogenic, and/or liquefied—of the gases. Warning: Do not abandon cylinders in the dock storage TABLE 4.2 Storage Limits for Flammable and Combustible Liquids for Laboratories: B Classification with Sprinkler System Class of Liquid Flash Point (oC) Amount (gallons per 100 square feet) Class I Flammable Below 38 4 Class II Combustible 38-60 4 Class IIIA Combustible 60-93 12 Class IIIB Combustible Above 93 Unlimited NOTE: Liquid (pumpable) flammable waste is included in the storage limitation. Non-pumpable waste is not included. Locations with an H (hazard) classification have much higher limits. Inside storage rooms for flammable liquids, the limits are from 5 to 10 gallons per square foot, depending on the size and construction of the room. SOURCE: NFPA (1991c), Chapter 2-2, "Laboratory Unit Fire Hazard Classification."

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals TABLE 4.3 Container Size for Storage of Flammable and Combustible Liquids   Flammable Liquidsa Combustible Liquidsb   Class IA Class IB Class IC Class II Class IIIA Container Liters Gallons Liters Gallons Liters Gallons Liters Gallons Liters Gallons Glassc 0.5 0.12 1 0.25 4 1 4 1 4 1 Metal or approved plastic 4 1 20 5 20 5 20 5 20 5 Safety cans 7.5 2 20 5 20 5 20 5 20 5 NOTE: Label safety cans with contents and hazard warning information. Safety cans containing flammable or combustible liquid waste must have appropriate waste labels. Place 20-L (5-gallon) and smaller containers of flammable liquids that are not in safety cans into storage cabinets for flammable liquids. Do not vent these cabinets unless they also contain volatile toxics or odoriferous chemicals. Aerosol cans that contain 21% (by volume), or greater, alcohol or petroleum base liquids are considered Class IA flammables. When space allows, store combustible liquids in storage cabinets for flammable liquids. Otherwise, store combustible liquids in their original (or other Department of Transportation-approved) containers according to Table 4.2. Store 55-gallon drums of flammable and combustible liquids in special storage rooms for flammable liquids. Keep flammable and combustible liquids away from strong oxidizing agents, such as nitric or chromic acid, permanganates, chlorates, perchlorates, and peroxides. Keep flammable and combustible liquids away from an ignition source. Remember that most flammable vapors are heavier than air and can travel to ignition sources. a Class IA includes those flammable liquids having flashpoints below 73 °F and having a boiling point below 100 °F, Class IB includes those having flashpoints below 73 °F and having a boiling point at or above 100 °F, and Class IC includes those having flashpoints at or above 73 °F and below 100 °F. b Class II includes those combustible liquids having flashpoints at or above 100 °F and below 140 °F, Class IIIA includes those having flashpoints at or above 140 °F and below 200 °F, and Class IIIB includes those having flashpoints at or above 200 °F. c Glass containers as large as 1 gallon can be used if needed and if the required purity would be adversely affected by storage in a metal or approved plastic container, or if the liquid would cause excessive corrosion or degradation of a metal or approved plastic container. SOURCE: NFPA (1991c), Chapter 7-2.3, "Storage." areas. Return them to the supplier when you are finished with them. For commonly used laboratory gases, it is prudent to consider the installation of in-house gas systems. Such systems remove the need for transport and in-laboratory handling of compressed gas cylinders. Chapter 5, section H, provides additional information on working with compressed gases in the laboratory. 4.E.5 Storing Highly Reactive Substances The following guidelines should be followed when storing highly reactive substances: Consider the storage requirements of each highly reactive chemical prior to bringing it into the laboratory. Consult the MSDSs or other literature in making decisions about storage of highly reactive chemicals. Bring into the laboratory only the quantities of material you will need for your immediate purposes (less than a 3- to 6-month supply, the length depending on the nature and sensitivity of the materials). Label, date, and inventory all highly reactive materials as soon as received. Make sure the label states, DANGER! HIGHLY REACTIVE MATERIAL! Do not open a container of highly reactive material that is past its expiration date. Call your institution's hazardous waste coordinator for special instructions. Do not open a liquid organic peroxide or peroxide former if crystals or a precipitate are present. Call your institution's hazardous waste coordinator for special instructions. Dispose of (or recycle) highly reactive material prior to expiration date. Segregate the following materials: oxidizing agents from reducing agents and combustibles, powerful reducing agents from readily reducible substrates, pyrophoric compounds from flammables, and perchloric acid from reducing agents. Store highly reactive liquids in trays large enough to hold the contents of the bottles. Store perchloric acid bottles in glass or ceramic trays. Store peroxidizable materials away from heat and light. Store materials that react vigorously with water away from possible contact with water. Store thermally unstable materials in a refrigerator. Use a refrigerator with these safety features: all spark-producing controls on the outside, a magnetic locked door, and an alarm to warn when the temperature is too high.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals Store liquid organic peroxides at the lowest possible temperature consistent with the solubility or freezing point. Liquid peroxides are particularly sensitive during phase changes. Inspect and test peroxide-forming chemicals periodically (these should be labeled with an acquisition or expiration date) and discard containers that have exceeded their safe storage lifetime. Store particularly sensitive materials or larger amounts of explosive materials in explosion relief boxes. Restrict access to the storage facility. Assign responsibility for the storage facility to one primary person and a backup person. Review this responsibility at least yearly. 4.E.6 Storing Toxic Substances The following precautions should be taken when storing toxic substances: Store chemicals known to be highly toxic (including carcinogens) in ventilated storage in unbreakable, chemically resistant secondary containers. Keep quantities at a minimum working level. Label storage areas with appropriate warning signs, such as CAUTION! REPRODUCTIVE TOXIN STORAGE or CAUTION! CANCER-SUSPECT AGENT STORAGE and limit access to those areas. Maintain an inventory of all highly toxic chemicals. Some localities require that inventories be maintained of all hazardous chemicals in laboratories. 4.F RECYCLING OF CHEMICALS, CONTAINERS, AND PACKAGING 4.F.1 General Considerations Recycling of chemicals can take many forms, from solvent distillation to cleaning of mercury to precipitation and purification of heavy metal salts. In each case a material that is not quite clean enough to be used as is must be brought to a higher level of purity or changed to a different physical state. Recycling processes can be very time-and energy-intensive and may not be economically justifiable. Before a decision on recycling is made, the cost of avoided waste disposal must be figured into the equation. Another significant issue is whether recycling activities require a waste treatment permit under the Resource Conservation and Recovery Act (RCRA). This issue is discussed in Chapter 9. State and local regulations must also be considered. A general comment applicable to all recycling is that a recyclable waste stream needs to be kept as clean as possible. If a laboratory produces a large quantity of waste xylene, small quantities of other organic solvents should be collected in a different container, because the distillation process will give a better product with fewer materials to separate. Steps should also be taken to avoid getting mercury into oils used in vacuum systems, oil baths, and other applications. Similarly, certain ions in a solution of waste metal salts may have a serious negative impact on the recrystallization process. It is also important to identify users for a recycled product so that time and energy are not wasted on producing a product that must still be disposed of as a waste. Recycling some of the chemicals used in large undergraduate courses may be especially cost effective because the needs of the users are known well in advance. Among the factors to be considered when ordering from a supplier of laboratory chemicals is whether the supplier will accept return of unopened chemicals, including highly reactive chemicals. Materials other than chemicals, such as containers or packaging materials and parts of laboratory instruments, can also be recycled. Examples include certain glass and plastic containers, drums and pails, plastic scrap and film scrap, cardboard, office paper, circuit boards, and metals such as steel and aluminum. 4.F.2 Solvent Recycling The choice of a distillation unit for solvent recycling is controlled largely by the level of purity desired in the solvent, and so it is useful to know the intended use of the redistilled solvent before equipment is purchased. A simple flask, column, and condenser setup may be adequate for a solvent that will be used for crude separations or for initial glassware cleaning. For a much higher level of purity, a spinning band column will probably be required. Stills with automatic controls that shut down the system under conditions such as loss of cooling or overheating of the still pot enhance the safety of the distillation operation greatly. Overall, distillation is likely to be most effective when fairly large quantities (roughly 5 L) of relatively clean single-solvent waste can be accumulated before the distillation process is begun. 4.F.3 Mercury Recycling The simplest method of cleaning mercury of entrained particulates or small quantities of water is

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals to allow the mercury to run very slowly through a tiny hole in a conical filter paper. The filter should be covered to reduce the evaporation of mercury. This method is slow but does produce a reasonably clean product that is adequate for a number of uses. Commercial recycling of mercury usually involves multiple distillations, resulting in a high-purity product. Distillation within the laboratory should be discouraged because it is very difficult to avoid contaminating the surrounding area with spilled or vaporized mercury. 4.F.4 Reclamation of Heavy Metals Inorganic qualitative analysis experiments typically include some toxic metal elements, such as cadmium, chromium, and lead. If the single-element "knowns" and "unknowns" can be collected separately, they can be readily precipitated for reuse in the next term's classes. Mixed samples can be precipitated and used as a starting material in a separations experiment. Although the amount of this type of waste may be quite small, it can require very expensive disposal if a commercial vendor must be used. Many recycling processes will result in some amount of residue that will not be reusable and will probably have to be handled as a hazardous waste. See Chapter 7 for further information.

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