Toxic Substances: (1) Exposure: Amount of a toxic substance to which an individual is exposed. This may represent the amount ingested, absorbed or inhaled or it may refer to the integral of concentration with time in the immediate environment. Where ambiguity may arise the basis used to define the exposure should be specified. (2) Dose: Used as a synonym with exposure. (3) Toxic: The property of substances which, when introduced into or absorbed by a living organism, destroy life or injure health. (4) Poison: Common term for a toxic substance. (5) Corrosive: In the context of toxic substances a corrosive substance is one, which may, on contact with living tissues, destroy them. (6) Acute: Immediate, short-term. Relating to exposure: conditions, which develop rapidly and may cause harm within a short time. Relating to effects: effects, which appear promptly after exposure. (7) Chronic: Persistent, prolonged and repeated. Relating to exposure: frequent, or repeated, or continuous exposure to substances. Relating to effects: when physiological effects appear slowly and persist for a longer period or with frequent recurrences. (8) Carcinogen: A substance, which produces cancer. (9) Toxicity: The relative power of a toxic material to cause harm. (10) Irritant: A non-corrosive material which may, through immediate prolonged or repeated contact with the skin or mucous membrane, cause pain, discomfort or minor injury. Such reactions may appear as a precursor to more serious injury. (11) Asphyxiation: Endangering life by causing a deficiency of oxygen. (12) Control Limit: An occupational exposure limit, which should not normally be exceeded. (13) Recommended Limit: An occupational exposure limit which is considered to represent good practice and a realistic criterion for the control of exposure, plant design, engineering controls and the selection and use of personal protective equipment. (14) Long Term Exposure Limit: A time weighted average concentration, usually average over 8 hours, which is appropriate for protecting against the effects of long term exposure. (15) Short Term Exposure Limit: A time weighted average concentration, usually average over 10 minutes, aimed at avoiding acute effects. (16) Threshold Limit Value-Time-Weighted Average (Tla-Twa): The time-weighted average concentration for a normal eight hour work day or 40-hour work week to which nearly all workers may be exposed, day after day, without adverse effect. (to be superseded by the term Control Limit). (17) Threshold Limit Value-Short-Term Exposure Limit (Tlvstel): The maximum concentration to which workers can be exposed for a period of up to 15 minutes continuously without suffering from (1) intolerable irritation, (2) chronic or irreversible tissue change, or (3) narcosis of sufficient degree to increase accident proneness, impair self-rescue or materially reduce work efficiently; provided that the daily TLV-TWA also is not exceeded. (18) Threshold Limit Value-Ceiling (Tlv-C): The concentration, which should not be exceeded even instantaneously. (19) Lethal Dose (LD): The quantity of material administered orally or by skin absorption which results in the death of 50% of the test group within a 14-day observation period. (20) Lethal Concentration (LC): The concentration of airborne material, the four-hour inhalation of which results in the death of 50% of test group within a 14-day observation period. (21) Immediately Dangerous To Life or Health (IDLH): Conditions such that an acute exposure will lead to acute or chronic effects.