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Highly Toxic

Definition

A highly toxic material is defined by the U.S. Occupational Health and Safety Administration (OSHA) in Appendix A as a chemical that falls in any of these three categories: A chemical that has a median lethal dose (LD50) of 50 milligrams or less per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 grams each. A chemical that has a median lethal dose (LD50) of 200 milligrams or less per kilogram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between two and three kilograms each. A chemical that has a median lethal concentration (LC50) in air of 200 parts per million by volume or less of gas or vapor, or 2 milligrams per liter or less of mist, fume, or dust, when administered by continuous inhalation for one hour (or less if death occurs within one hour) to albino rats weighing between 200 and 300 grams each.

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MSDS Relevance

This is the greatest level of toxicity defined in the OSHA Hazard Communication Standard (OSHA does not have an "Extremely toxic" ranking). A separate OSHA standard, Process Safety Management of Highly Hazardous Chemicals", 29 CFR 1910.119, applies to workplaces where highly toxic materials are used. See Further Reading below for resources on this standard.

Accidental release or exposure to a highly toxic chemical can cause serious injury or death. If you can not avoid using highly toxic materials in the first place, then proper personal protective equipment (gloves, safety goggles, respirators etc.) and engineering controls such as fume hoods are an absolute necessity.

It is critical that you develop and enforce written standard operating procedures (SOP's) for working with each highly toxic material. In 1997, a professor at Dartmouth University (an experienced researcher and expert on the toxicology of heavy metal poisoning) died after spilling just a few drops of highly toxic dimethylmercury on her latex gloves (the wrong choice of gloves, obviously). In 2009, a worker in Canada died when he performed a chemical reaction in a fume hood that had been deactivated for maintenance; following an SOP to test all hoods before use would have saved his life.

Part of your experiment procedure planning must include knowing the physical properties of the material as well as symptoms of exposure and first aid procedures. Never work with highly toxic materials while alone. If one exists, have the proper antidote on hand.

Further Reading

• The OSHA Standard "Process Safety Management of Highly Hazardous Chemicals", 29 CFR 1910.119 applies to those using highly toxic materials on an industrial scale.
• OSHA's web site devoted to Process Safety Management (PSM).
• OSHA's fact sheet Highly Hazardous Chemicals (68 K PDF download).
• Brookhaven National Lab has a List of Highly Acute Toxins that includes the lethal doses.
• Highly Toxic and Toxic Materials, Chapter 37 of the Virginia State Fire Prevention Code.
• Play Toxic Trivia at ILPI.

See also: LC₅₀, LD₅₀, toxic.

Additional definitions for metric system from Google and OneLook.

Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.