MSDS Definitions

Page Updated January 2008

Maximum Acceptable Ambient Concentration (MAAC): The maximum allowable twenty-four hour average concentration, in ambient air, of a toxic air contaminant.
Occupational Exposure Limit (OEL): The most restrictive eight-hour time weighted average concentration specified for workroom air selected from either the 1986-1987 Threshold Limit Values and Biological Exposure Indices as adopted by the American Conference of Governmental Industrial Hygienists; the Recommended Standards for Occupational Exposure set forth in the July 1985 summary of National Institute for Occupational Safety and Health Recommendations for Occupational Health Standards; or the 1986 Workplace Environmental Exposure Levels set forth by the American Industrial Hygiene Association.
Median Lethal Concentration (LC50): The atmospheric concentration found to be lethal to 50 percent of a group of test animals exposed for the specified time period.
Median Lethal Dose (LD50): The dose found to be lethal in 50 percent of a group of test animals when administered by the specified route, e.g., oral or dermal.
Threshold Limit Value (TLV): Airborne concentration of substances established by the American Conference of Governmental Industrial Hygienists, which represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse effect.
Substances of High Toxicity: Those chemicals having an acute toxicity of either (1) Median Lethal Dose, single oral dose, rate, less than or equal to 50 mg/kg, or (2) Median Lethal Concentration, four-hour inhalation exposure, rat, less than or equal to 100 ppm, or (3) Median Lethal Dose, dermal exposure, rabbits, less than or equal to 100 mg/kg.
Substances of Moderate Toxicity: Those substances that have been shown to produce moderate toxicity following exposure or have been demonstrated to produce carcinogenic, mutagenic, or teratogenic action in a single animal species with little or no human evidence of carcinogenic, mutagenic, or teratogenic action, or those chemicals having an acute toxicity of either (1) Median Lethal Dose, single oral dose, rat, greater than 50 mg/kg but less than 500 mg/kg, or (2) Median Lethal Concentration, four-hour inhalation exposure, rat, greater than 100 ppm but less than 1,000 ppm, or (3) Median Lethal Dose, dermal exposure, rabbits, greater than 100 mg/kg but less than 500 mg/kg.
Substances of Low Toxicity: Those substances that have been shown to produce low toxicity or irritation, or those chemicals having an acute toxicity of either (1) Median Lethal Dose, single oral dose, rat, greater than 500 mg/kg but less than 5 g/kg, or (2) Median Lethal Concentration, four-hour inhalation exposure, rat, greater than 1,000 ppm but less than 10,000 ppm, or (3) Median Lethal Dose, dermal exposure, rabbits, greater than 500 mg/kg but less than 3,000 mg/kg.
Suspect Human Carcinogen: A substance suspected of inducing cancer based on human evidence or demonstration by appropriate methods, or carcinogenesis in two or more animal species or strains.
Confirmed Human Carcinogen: Substances recognized to have carcinogenic or cocarcinogenic potential in humans.
Best Available Control Technology (BACT): The best control technology that is available for each contaminant. This determination will be made by the Commissioner on a case-by-case basis taking into account energy, environmental, health risk, costs and economic impacts of alternative control systems.