Work with highly toxic chemicals or select carcinogens require special containment practices in addition to those described in Chapter 6 for toxic chemicals. Highly toxic compounds have the ability to cause harmful effects, which can be local or systemic, after a single exposure. Among the most useful parameters for assessing the risk of acute toxicity of a chemical are its LD50 and LC50 values, the mean lethal dose or lethal concentration causing death in experimental animals. Per the Health Hazards Definitions of the OSHA Hazard Communication Standard, a substance is highly toxic if:
- the oral LD50 for albino rats is less than 50 mg/kg or
- the topical LD50 for albino rabbits is less than 200 mg/kg or
- the LC50 in albino rats is less than 200 ppm for one hour.
Examples of highly toxic substances include hydrogen cyanide, osmium tetroxide, phosgene, sodium azide, and tetrodotoxin. For a thorough (but not exhaustive) list of highly toxic substances, refer to Appendix 7-A.
A select carcinogen is a chemical agent that causes a malignant disease or statistically increases the risk of cancer, whether by initiation or promotion. Appendix 7-B lists select carcinogens that are:
- listed as a known or reasonably anticipated human carcinogen in the biennial Report on Carcinogens published by the National Toxicology Program
- listed as carcinogenic to humans (Group 1), probably carcinogenic to humans (Group 2A), or possibly carcinogenic to humans (Group 2B) by the International Agency for Research on Cancer (IARC)
- regulated by OSHA as a carcinogen
Some of these compounds are common materials used in many laboratories, such as acrylamide, chloroform, carbon tetrachloride, benzene, hydrazine, and thiourea. More than two-thousand substances exhibit some evidence for carcinogenicity. Many of these also warrant careful planning and control procedures.