biological, or radioactive waste. Each option should be ranked, ordered, and prioritized according to the degree of risk posed. Any combination of methods that poses unacceptable risk to waste handlers should be rejected.

Chemical-Radioactive Waste

The management of mixed waste (chemical-radioactive) is often complicated by regulations whose application to a particular case is inconsistent with the relative risk posed by each component hazard. For example, chemical waste containing short-half-life radionuclides is managed best by being held for a period long enough to allow safe decay (e.g., 10 half-lives, but not to exceed 2 years). However, EPA regulations and state laws may limit storage of hazardous chemical waste to 90 days. Chemical-radioactive (mixed) waste is difficult to deal with, primarily because of EPA regulations that prevent on-site storage until de minimis levels of radioactivity can be reached and stringent U.S. NRC regulations for the management of low-activity radioactive waste that poses no significant risk to the public or the environment. Used flammable liquid scintillation cocktails, phenol/chloroform nucleic acid extractants from radioactive cells, neutralized radioactive trichloroacetic acid solutions, and some gel electrophoresis waste are examples of chemical-radioactive waste. Techniques for minimizing these types of waste include the use of nonhazardous chemical substitutes so that the waste can be handled simply as radioactive and treated by U.S. NRC "decay-in-storage" regulations. In some cases, EPA-approved chemical hazard reduction methods may be applied and the waste treated as radioactive.

Chemical-Biological Waste

Most, but not all, chemical-biological waste is best dealt with as chemical waste after due consideration is taken of special restrictions that may apply to the biological component if it is putrescible, infectious, or biohazardous. Incineration as a hazardous chemical is usually preferable because animal and medical waste incinerators are not licensed to burn regulated chemical waste. Many types of biological fluid waste containing chemical components can be disposed of in the sanitary sewer, but local approval may be required. Autoclaving can sterilize infectious waste, which then can be treated as chemical waste. However, autoclaving may volatilize chemicals, which could then pose hazards to personnel or could damage the autoclave. Waste and "sharps" of all kinds from laboratories working with hepatitis B or human immunodeficiency viruses must be handled with special care under the OSHA Blood borne Pathogen Standard.

Radioactive-Biological Waste

If short-half-life radionuclides are present, decay-in-storage until U.S. NRC regulations allow disposal as biological waste is the appropriate strategy for radioactive-biological waste. Preliminary disinfection or freezing should be used to protect personnel who handle putrescible waste during radionuclide decay. Appropriate options for ultimate disposal are incineration after the waste has reached U.S. NRC-approved levels of radioactivity or alkaline digestion and submission to the sanitary sewer in accordance with local regulations. Particular attention must be given to the handling or cleaning of radioactive laboratory ware, and to the proper disposal of needles, broken glassware, or sharps from biological or medical laboratories.

Chemical-Radioactive-Biological Waste

As indicated above, a combination of waste types may be very difficult to deal with and should always be considered case by case. Decay-in-storage to acceptable levels of radioactivity can reduce the problem to that of handling chemical-biological waste. Autoclaving or use of a disinfectant may be needed to reduce the hazard of biological waste during storage. Unlike the radioactive and biological component of a multihazardous waste, the chemical content does not usually vary significantly with time, although the possibility of treatment to convert hazardous chemical content to nonhazardous should be considered as part of the overall approach to waste management. Before initiating any experiment that might lead to chemical-biological-radioactive waste, researchers are advised to consult with their environmental health and safety office and/or waste removal contractor to avoid an intractable disposal situation. Growing recognition by regulatory agencies of the special problems of multihazardous waste management offers hope that disposal will become increasingly manageable.

LABORATORY FACILITIES (CHAPTER 8)

Chemical laboratories are the most common type of workplace where a wide variety of chemicals are handled on a routine basis. They have evolved into unique facilities designed to deal with many of the hazards described in this book. Chapter 8 discusses the modern laboratory environment as an essential component of the culture of safety and outlines the important role of safety inspection programs. Labora-



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