best by maintaining a comprehensive, reliably updated inventory, especially in a large institution. Maintaining a readily accessible inventory can be expedited if all chemicals are bar-coded and records of their status are continuously updated and made available through computer networking (see "Recommendations" below). Manufacturers and vendors of laboratory chemicals also can play an increasingly valuable role by responding to the needs of their customers to reduce the scale of experimentation, maintain continuously updated inventories accessible over networks, and reduce the cost of waste disposal.

The costs of acquisition, storage, and disposal can be minimized by conducting experiments on the smallest practical scale, a practice that also reduces the risk of hazards from exposure, fire, and explosion. Microscale reactions can now be run conveniently with less than 100 milligrams of solids or 100 microliters of liquids, compared with the traditional 10 to 50 grams and 100 to 500 milliliters.

Traditionally, the hazardous properties of chemicals have been regarded as a significant factor in planning experiments only if extreme toxicity or danger from explosion was apparent. The present emphasis on reducing risks and waste of all kinds may suggest the substitution of different solvents or less hazardous synthetic routes. Although it may not always be feasible to improve safety through the use of more benign materials, it is always appropriate to consider the possibility of reducing risks in this way, especially if precedents for the planned work were taken from the older literature, where safety and pollution problems were afforded less weight than is now given to them.

WORKING WITH CHEMICALS (CHAPTER 5)

Chapter 5 is a comprehensive manual for the safe handling of hazardous chemicals commonly used in laboratories. Like Chapters 3 and 6, Chapter 5 is intended to be used as a daily reference guide to appropriate standards of professional laboratory performance. In addition to discussing handling of chemicals in a variety of specific circumstances, it addresses issues such as proper protective clothing, good housekeeping, and necessary preparation for accidents and concludes with an alphabetical listing of especially hazardous materials.

WORKING WITH LABORATORY EQUIPMENT (CHAPTER 6)

Chapter 6 explains how to use the various kinds of equipment associated with handling hazardous chemicals. Although dangers such as electrical shock from bad wiring, falls on flooded floors, or cuts from broken glassware are not unique to the laboratory workplace, their consequences for laboratory personnel can be compounded because of the added hazards of toxicity, flammability, corrosiveness, and reactivity that characterize many chemicals. The accidental dropping of a glass container of a volatile poison or the fire hazard from sparking electrical equipment or switches in the presence of flammable fumes, for example, present potentially serious situations of a kind that must be kept in mind when laboratory experiments are planned and conducted.

The special hazards that accompany the use of electrical equipment (e.g., stirrers, pumps, and heating/ cooling devices), the precautions necessary for handling gases in various containers and systems, and the equipment for dealing with and preventing many kinds of laboratory accidents are discussed in detail.

DISPOSAL OF WASTE (CHAPTER 7)

Concern about the fate of used or unwanted products of chemical reactions has not been a significant part of the traditional culture of laboratory workers. To emphasize the high priority that waste disposal has assumed in modern laboratory operations, the committee was charged to merge the subject matter of Prudent Practices 1983 on the disposal of waste from laboratories with that of Prudent Practices 1981 on the handling of hazardous chemicals in laboratories. Furthermore, it was asked to investigate the especially vexing problems of handling multihazardous chemical, biological, and radioactive waste and to propose recommendations for dealing with it. These are offered in Chapter 7. In view of the crucial role of regulations in dealing with laboratory waste, Chapter 9 on governmental regulation of laboratories should be referred to frequently as background for Chapter 7.

Waste is generally defined as excess, unneeded, or unwanted material. Because these terms are fairly subjective, regulatory agencies have attempted to provide more objective and specific definitions. However, the regulatory viewpoint that a material is waste if it is abandoned or "inherently wastelike" remains inescapably subjective. Although the residues from cleaned-up spills are obviously waste, the point at which a laboratory worker decides that a given chemical is no longer potentially useful may be difficult to define. Once the determination has been made, the waste must be handled within the constraints of legal guidelines that are usually defined according to the nature of the waste (chemical, radioactive, biological), the type and degree of hazard that it presents, and its quantity. Enlightened risk management also dictates



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