Also known as 'blistering agents' or 'mustard agents', vesicants (delivered in either gas or liquid form) produce burns and blisters on the skin, eyes, throat and even internal organs. If they pass into the blood stream vesicants act as poisons. If they reach the respiratory system, they can cause death by asphyxiation.
The most well-known vesicant substance is mustard gas.
Mustard gas attacks the whole body and is a carcinogenic (it induces cancer). In the event of exposure, the effects of mustard gas may take up to 24 hours before they start to become apparent. Mortality rates from mustard gas are relatively low. Those who die usually do so between about two days and about two weeks after exposure. Lewisite is also a vesicant. There is no antidote to the effects of vesicant agents, we can only treat the symptoms.
Choking agents are relatively simple substances, most of which are either common industrial chemicals (like chlorine, and phosgene) or their derivatives. Choking agents are delivered in gas form and are more volatile than vesicants (which means they will disperse in the air more quickly). They act exclusively by inhalation, targeting the nose, lungs and throat, provoking an immediate smothering effect followed by oedema (excess fluid) of the lung possibly resulting in death by asphyxiation.
Blood agents like cyanhydric acid and hydrogen cyanide, are cyanide-based poisons that enter the blood stream disrupting cellular functions in the respiratory system producing suffocation as the victim 'drowns' in his/her own blood supply. Hydrogen cyanide (in gas or liquid form) is poisonous to inhale and can also be absorbed by the skin.
Early symptoms of cyanide poisoning include restlessness, headache, palpitations and difficulties breathing, followed by vomiting, convulsions, respiratory failure and unconsciousness. Cyanhydric acid was used by the Nazis in the gas chambers. And although no documented evidence exists, Iraq is believed to have used hydrogen cyanide against the Kurds in the 1980s.
Hydrogen cyanide is volatile which means that it disperses quickly so it's difficult to build up a high concentration outdoors. However, in a confined space, it quickly reaches lethal levels of concentration. In this scenario, there may not be time to display early symptoms with victims just suddenly falling dead. Like choking agents, these are common industrial chemicals that are relatively easy to find and produce. There is no antidote for cyanide poisoning.
Nerve agents (neurotoxins) like sarin, tabun (developed by Nazi Germany during the 1930s), soman or VX produce their deadly effect by blocking an enzyme that is necessary for the central nervous system to function. This leads to a disruption of muscle function followed by a seizure and, eventually, death.
Nerve agents (in either gas or liquid form) enter the body through inhalation, through skin absorption or through being consumed (for example, in a contaminated water supply). Generally the symptoms are produced faster when inhaled (2 to 3 minutes) than when they are absorbed or consumed (20 to 30 minutes).
A thimble-sized portion of one of these nerve toxins can kill a person in minutes. A few particles can produce death in 24 hours. Nerve agents pose a real threat because they’re relatively easy and cheap to manufacture (they're made from ingredients used in the manufacture of insecticides, fertilizers and certain coloring agents).