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:

  1. listed as a known or reasonably anticipated human carcinogen in the biennial Report on Carcinogens published by the National Toxicology Program
  2. 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)
  3. 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.