3.A INTRODUCTION

A key element of planning an experiment involves assessing the hazards and potential risks associated with the chemicals and laboratory operations to be employed in a proposed experiment. This chapter provides a practical guide for the laboratory worker engaged in these activities. Section 3.B introduces the sources of information where laboratory workers can find data on toxic, flammable, reactive, and explosive chemical substances as well as physical, biological, and radioactive hazards. Section 3.C discusses the toxic effects of laboratory chemicals. The first part of this section presents the basic principles that form the foundation for evaluating hazards for toxic substances. The remainder of the section describes how the laboratory worker can use this understanding and the sources of information introduced above to assess the risks associated with potential hazards of chemical substances and then to select the appropriate level of laboratory practice as discussed in Chapter 5. Sections 3.D and 3.E present guidelines for evaluating hazards associated with the use of flammable, reactive, and explosive substances and physical hazards, respectively. Finally, there is a brief reference to biohazards and hazards from radioactivity in sections 3.F and 3.G, respectively.

Although the responsibility for carrying out the hazard evaluations and risk assessments described here generally lies primarily with the laboratory worker who will actually be conducting the proposed experiment, this activity often requires consultation with other colleagues and superiors. For example, depending on the level of training and experience of the laboratory worker, the involvement of the worker's immediate laboratory supervisor may be advisable and in some instances essential. In addition, many institutions have environmental health and safety offices, where industrial hygiene specialists are available to advise laboratory workers and their supervisors on issues involved in the assessment of risks of laboratory chemicals. Chemical hygiene officers, required by federal regulation, play similar departmental roles in many institutions.

3.B SOURCES OF INFORMATION

3.B.1 Chemical Hygiene Plan

Beginning in 1991, every laboratory in which hazardous chemicals are in use has been required by federal law to have a written Chemical Hygiene Plan (CHP), which includes provisions capable of protecting personnel from the ''health hazards associated with the chemicals present in that laboratory." All laboratory workers should be familiar with and have ready access to their institution's CHP. In some laboratories, CHPs include standard operating procedures for work with specific chemical substances, and in these cases the CHP may be sufficient as the primary source of information used for risk assessment and experiment planning. However, most CHPs provide only general procedures for handling chemicals, and in these cases prudent experiment planning requires that the laboratory worker consult additional sources for information on the properties of the substances that will be encountered in the proposed experiment.

3.B.2 Material Safety Data Sheets

Federal law requires that manufacturers and distributors of chemicals provide users with Material Safety Data Sheets (MSDSs), which are designed to provide the information needed to protect users from any hazards that may be associated with the product. MSDSs have become the primary vehicle through which the potential hazards of materials obtained from commercial sources are communicated to the laboratory worker. Institutions are required by law to retain and make readily available to workers the MSDSs provided by chemical suppliers.

As the first step in a risk assessment, laboratory workers should examine their plan for a proposed experiment and identify the chemicals whose toxicological properties they are not already familiar with from previous experience. The MSDS for each unfamiliar chemical should then be examined. Procedures for accessing MSDS files vary from institution to institution. In some cases, MSDS files may be present in each laboratory, while in many cases complete files of MSDSs are maintained only in a central location, such as the institution's environmental health and safety office. Some laboratories now have the capability to access MSDSs electronically, either from CD-ROM disks or via computer networks. As a last resort, the laboratory worker can always contact the chemical supplier directly and request that an MSDS be sent by mail.

MSDSs are concise technical documents, generally two to five pages in length. An MSDS typically begins with a compilation of data on the physical, chemical, and toxicological properties of the substance and then provides generally concise suggestions for handling, storage, and disposal. Finally, emergency and first aid procedures are usually outlined. At present there is no required format for an MSDS; however, it is expected that the Occupational Safety and Health Administration (OSHA) will soon adopt a general 16-part format proposed by the American National Standards Insti-



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