Hazards
Pyridine has a flash point (the lowest temperature at which it can vaporize to form an ignitable mixture in air) of only 17 °C and is therefore highly flammable. Its ignition temperature is 550 °C, and mixtures of 1.7–10.6 vol% of pyridine with air are explosive. The thermal modification of pyridine starts above 490 °C, resulting in bipyridine (mainly 2,2'-bipyridine and to a lesser extent 2,3'-bipyridine and 2,4'-bipyridine), nitrogen oxides and carbon monoxide. Pyridine easily dissolves in water and harms both animals and plants in aquatic systems. The permitted maximum allowable concentration of pyridine was 15–30 parts per million (ppm, or 15–30 mg·m−3 in air) in most countries in the 1990s, but was reduced to 5 ppm in the 2000s. For comparison, indoor air contaminated with tobacco smoke may contain up to 16 µg·m−3, and one cigarette contains 21–32 µg of pyridine.
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