Physical Characteristics

The toxic action of phosgene is typical of a certain group of lung-damaging agents. Phosgene is the most dangerous member of this group and the only one considered likely to be used in the future. Phosgene was used for the first time in 1915, and it accounted for 80% of all chemical fatalities during World War I.

Phosgene is a colorless gas under normal temperature conditions.
Its boiling point is 8.2 degrees C, making it an extremely volatile and non-persistent agent.
Its vapor density is 3.4 times that of air.
It may therefore remain for long periods of time in basements and other low lying areas.
In low concentrations it has a smell resembling newly mown hay.