Poison gas is any type of noxious gas that is used to harm or kill living things intentionally. Poison gas warfare, sometimes known as chemical warfare, came into wide use during World War I, when mustard gas was used to harm the troops fighting in trenches.
Chemical warfare during World War I used mostly chlorine and phosgene gases released from canisters and spread by the wind. These substances settled in trenches and killed more than 90,000 people throughout the conflict. More than 124,000 ton of poison gas was dispersed. Those who survived a chemical attack suffered ill effects for the rest of their lives.
Modern chemical weapons include deadlier substances and faster methods of delivery. Nerve agents and sarin gas made headlines in the 1980s and 1990s when Iraq used mustard gas on Kurds and Japanese terrorists applied sarin to civilians in a subway attack. Poison gas can be dispersed through missiles, landmines, artillery shells, bombs and spray tanks.
Purdue University lists 85 chemicals as poison gases, more than half of which are noted to be toxic or highly toxic. Exposure to some of the most toxic gases reach poisonous levels at less than one part per million over a 15-minute span. Poison gas should be handled with extreme care and only after specialized training.