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A substance is pyrophoric (from Ancient Greek: πυροφόρος, pyrophoros, 'fire-bearing') if it ignites spontaneously in air at or below 54 °C (129 °F) (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). [1] Examples are organolithium compounds and triethylborane.
Division 4.2: Spontaneously Combustible . Spontaneously combustible material is: Pyrophoric Material: A pyrophoric material is a liquid or solid that, even in small quantities and without an external ignition source, can ignite within five (5) minutes after coming in contact with air when tested according to the UN Manual of Tests and Criteria.
A flammable liquid is a liquid which can be easily ignited in air at ambient temperatures, i.e. it has a flash point at or below nominal threshold temperatures defined by a number of national and international standards organisations.
The GHS transport pictograms are the same as those recommended in the UN Recommendations on the Transport of Dangerous Goods, widely implemented in national regulations such as the U.S. Federal Hazardous Materials Transportation Act (49 U.S.C. 5101–5128) and D.O.T. regulations at 49 C.F.R. 100–185.
Pyrophoric liquids are liable to ignite after 5 minutes of coming in contact with air. Pyrophoric solids follow the same criteria as pyrophoric liquids. Self-heating substances, which differ from self-reactive substances in that they will only ignite in large quantities (kilograms) and after a long duration of time (hours or days).
NFPA 704 safety squares on containers of ethyl alcohol and acetone. "NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response" is a standard maintained by the U.S.-based National Fire Protection Association.
Hazard statements form part of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). They are intended to form a set of standardized phrases about the hazards of chemical substances and mixtures that can be translated into different languages.
Many gases have toxic properties, which are often assessed using the LC 50 (median lethal concentration) measure. In the United States, many of these gases have been assigned an NFPA 704 health rating of 4 (may be fatal) or 3 (may cause serious or permanent injury), and/or exposure limits (TLV, TWA/PEL, STEL, or REL) determined by the ACGIH professional association.