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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
disposal of all waste generated. The sequence of steps for planning is so fundamental and repeatable that the committee has structured this book in accordance with the work-flow diagram, Figure 1.2, given in Chapter 1. Each chapter is organized around a key step in that protocol.
There is great diversity in the formality and means by which the planning structure applies. For example, laboratory manuals for students provide a complete package of planned experiments and detailed technical directions. Future manuals should include questions and assignments that involve the student actively in considering the risks, regulations, and waste disposal costs for alternative approaches to the problem under discussion. In research laboratories where important steps of the planning process have, over time, become standard operating procedure, mental planning may be sufficient to enable doing the next routine experiment safely and effectively. In contrast, a completely new type of experiment involving unfamiliar materials and unprecedented hazards may require formal planning for every stage, and discussion with experts outside the immediate research group and members of the environmental health and safety office should be considered carefully.
EVALUATING HAZARDS AND ASSESSING RISKS IN THE LABORATORY (CHAPTER 3)
A first step in planning a new experiment is consideration of the types of hazards that may be posed by toxic, flammable, reactive, and/or explosive materials encountered in the proposed work. Even if the experiment is part of a series that has been repeated so many times that every step has become routine, the change in conditions or compounds that makes this a new experiment, rather than just a repetition, may introduce a new hazard, unprecedented in the series; for example, a minor molecular modification may result in a sharp increase in toxicity or likelihood of explosion.
Thus, planning for the first experiments in a new field, as well as experiment planning by inexperienced workers, requires considerable investigation of published resources and discussion with competent experts on potential technical hazards and regulatory requirements. Advice from environmental health and safety or industrial hygiene personnel may be particularly valuable in the initial stage of planning.
A wide variety of published resources describe the dangerous properties of specific compounds. All of the common types of explosive, reactive, and flammable compounds are well documented. Because the functional groups that are associated with these properties are clearly identified, and their hazards well known, it is usually possible to predict the potential for a serious accident. However, unprecedented accidents are reported occasionally, and new substances with unknown properties are continually being generated as products and by-products of chemical experiments.
At the present time, the least predictable dangerous chemical property is toxicity. In addition to discussing toxicity extensively, Chapter 3 provides general guidelines and references to specific toxicological information. Unless there is very well established evidence that a chemical is innocuous, the following warnings should always be borne in mind:
Assume that all chemicals encountered in the laboratory are potentially toxic to some degree. Because the risk posed by a toxic chemical depends on the extent of exposure and the chemical's inherent toxicity, minimize exposure by avoiding skin contact and inhalation exposure through proper clothing and ventilation as habitual safe practice.
Treat any mixture of chemicals as potentially more toxic than its most toxic component.
Treat all new compounds, or those of unknown toxicity, as though they could be acutely toxic in the short run and chronically toxic in the long run. Because typical reactions produce a variety of by-products that are often unidentified or unknown, reaction products should be assumed to be toxic during work-up. Even though the likelihood is small that any given unknown chemical is very toxic, and the potential dose is usually low, laboratory researchers and workers may be exposed to thousands of chemicals during a professional lifetime, and there is a reasonable probability of eventual dangerous accidental exposure to a toxic substance. A habit of minimizing exposure should be cultivated.
The flammability, corrosiveness, and explosibility of chemicals and their combinations must also be considered along with toxicity in evaluating hazards and planning how to deal with them. In addition, wise risk management requires taking into account the amount of material to be used in an experiment.
Chapters 3, 5, and 6 are the heart of this volume because of their detailed guidelines regarding laboratory hazards and procedures. The content of these chapters inevitably overlaps because assessing the risks of a given procedure with a given chemical (Chapter 3) may also suggest the best ways to work with it (Chapters 5 and 6). Some of the most notable laboratory hazards arise from the interactions of equipment with chemicals (e.g., fires from sparking motors near flammable vapors) or from special nonchemical properties such as radioactivity or biological contamination.