The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
TABLE 3.6 Examples of Reproductive Toxins
Arsenic and certain arsenic compounds
Cadmium and certain cadmium compounds
Ethylene glycol monomethyl and ethyl ethers
defects. Embryotoxins have the greatest impact during the first trimester of pregnancy. Because a woman often does not know that she is pregnant during this period of high susceptibility, women of childbearing potential are advised to be especially cautious when working with chemicals, especially those rapidly absorbed through the skin (e.g., formamide). Pregnant women and women intending to become pregnant should seek advice from knowledgeable sources before working with substances that are suspected to be reproductive toxins. As minimal precautions, the general procedures outlined in Chapter 5, section 5.D, should then be followed for work with such compounds.
Information on reproductive toxins can be obtained from LCSSs, MSDSs, and by consulting safety professionals in the environmental safety department, industrial hygiene office, or medical department of the worker's institution. Literature sources of information on reproductive and developmental toxins include the Catalog of Teratogenic Agents (Shepard, 1992), Reproductively Active Chemicals: A Reference Guide (Lewis, 1991), and "What Every Chemist Should Know About Teratogens" in the Journal of Chemical Education (Beyler and Meyers, 1982). Table 3.6 lists some common materials that are suspected to be reproductive toxins. In some cases it will be appropriate to handle these compounds as particularly hazardous substances using the special additional precautions outlined in section 5.D.
3.DFLAMMABLE, REACTIVE, AND EXPLOSIVE HAZARDS
In addition to the hazards due to the toxic effects of chemicals, hazards due to flammability, explosibility, and reactivity need to be considered in risk assessment. These hazards are described in detail in the following sections. Further information can be found in Bretherick's Handbook of Reactive Chemical Hazards (Bretherick, 1990), an extensive compendium that is the basis for the lists of incompatible chemicals included in various reference works. Bretherick describes computational protocols that consider thermodynamic and kinetic parameters of a system to arrive at quantitative measures such as the Reaction Hazard Index (RHI). So-called "reactive" hazards arise when the release of energy from a chemical reaction occurs in quantities or at rates too great for the energy to be absorbed by the immediate environment of the reacting system, and material damage results. In addition, the "Letters to the Editor" column of Chemical & Engineering News routinely reports incidents with explosive reaction mixtures or conditions.
3.D.1.1 Flammable Substances
Flammable substances, those that readily catch fire and burn in air, may be solid, liquid, or gaseous. The most common fire hazard in the laboratory is a flammable liquid or the vapor produced from such a liquid. An additional hazard is that a compound can enflame so rapidly that it produces an explosion. Proper use of substances that can cause fires requires knowledge of their tendencies to vaporize, ignite, or burn under the variety of conditions of use in the laboratory.
For a fire to occur, three conditions must exist simultaneously: an oxidizing atmosphere, usually air; a concentration of flammable gas or vapor that is within the flammable limits of the substance; and a source of ignition. In most situations, oxygen or air is present. Prevention of the coexistence of flammable vapors and an ignition source is the optimal way to deal with the hazard. When the vapors of a flammable liquid cannot always be controlled, strict control of ignition sources is the principal approach to reduction of the risk of flammability. The rates at which different liquids produce flammable vapors depend on their vapor pressures, which increase with increasing temperature. The degree of fire hazard of a substance depends also on its ability to form combustible or explosive mixtures with air and on the ease of ignition of these mixtures. Also important are the relative density and solubility of a liquid with respect to water and of a gas with respect to air. These characteristics can be evaluated and compared in terms of the following specific properties.
3.D.1.2 Flammability Characteristics
The flash point is the lowest temperature at which a liquid has a sufficient vapor pressure to form an ignitable mixture with air near the surface of the liquid. Note that many common organic liquids have a flash point below room temperature: for example, acetone (-18 °C), benzene (-11.1 °C), diethyl ether (-45 °C),