Poison gas, a term evoking images of trench warfare, is a broad label for chemical substances deliberately deployed to cause harm. These agents are designed to incapacitate, injure, or kill by exploiting the body’s biological functions. Understanding these chemical warfare agents (CWAs) is important not only due to their historical use but also because of the ongoing global efforts to prevent their re-emergence as a weapon of conflict.
Defining Poison Gas and Chemical Warfare
“Poison gas” is the common term for Chemical Warfare Agents (CWAs), which are toxic chemicals and their precursors designed for weaponization. CWAs are toxic substances delivered through a dispersal system, such as an aerosol, liquid spray, or true gas. Their effect is immediate or rapid following exposure.
Chemical warfare involves the tactical use of these agents to cause mass casualties or deny an area to personnel. A key differentiation is made between purpose-built CWAs, like Sarin, and Toxic Industrial Chemicals (TICs), such as chlorine or ammonia. TICs are chemicals produced for commercial use, but because of their toxicity, they can be weaponized; Phosgene, a CWA in World War I, is also used in plastics manufacturing, illustrating this overlap.
Major Categories of Chemical Agents
Chemical agents are systematically categorized based on the primary physiological effects they induce on the human body. The most recognized categories are nerve, blister, choking, and blood agents. These classifications allow for the rapid identification and treatment of victims following an attack.
Nerve agents, such as Sarin (GB) and VX, are among the most lethal CWAs, acting quickly to disrupt the central nervous system. Blister agents, also known as vesicants, include Sulfur Mustard and Lewisite. They are designed to cause severe blistering of the skin, eyes, and lungs. Their effects are often delayed, but they inflict painful, deep burns and tissue damage.
Choking agents, including Chlorine and Phosgene, primarily target the respiratory system. Exposure results in severe irritation of the airways and, critically, causes fluid buildup in the lungs, a condition known as pulmonary edema. Blood agents, such as hydrogen cyanide, are systemic asphyxiants that rapidly interfere with the body’s ability to utilize oxygen at a cellular level, leading to sudden collapse.
Physiological Mechanism of Harm
The lethality of CWAs stems from their ability to interfere with fundamental biological processes at a molecular level. Nerve agents exert their effect by inhibiting the enzyme acetylcholinesterase (AChE) in the nervous system. This inhibition prevents the breakdown of the neurotransmitter acetylcholine, leading to a continuous over-stimulation of muscles and glands that ultimately causes respiratory failure and death in minutes.
Blister agents operate as powerful alkylating agents, meaning they chemically attach alkyl groups to biomolecules like DNA and proteins within cells. This chemical modification causes extensive damage and necrosis, or cell death, particularly in tissues with rapid cell turnover such as the skin, eyes, and the lining of the respiratory tract.
Choking agents, like Phosgene, react with the water present in the moist lining of the lungs. This reaction forms hydrochloric acid and other destructive compounds, which destroy the delicate alveolar-capillary membranes, causing the lungs to fill with fluid.
Blood agents, specifically cyanide compounds, interfere with the process of mitochondrial respiration. They achieve this by binding to cytochrome oxidase, a protein complex inside the cell that is necessary for the final stage of cellular energy production. By blocking this step, the cells are unable to use oxygen, causing internal asphyxiation even though the victim may be breathing adequate air, leading to rapid loss of consciousness and cardiac failure.
Historical Context and International Regulation
The first large-scale use of chemical weapons occurred during World War I, where choking agents like chlorine and later vesicants like mustard gas caused over a million casualties. This shocking demonstration of toxic warfare led to the 1925 Geneva Protocol, which banned the use, but not the development or possession, of chemical and biological weapons. This initial effort laid the groundwork for future international control.
The current comprehensive framework is the Chemical Weapons Convention (CWC), which entered into force in 1997 and is administered by the Organisation for the Prohibition of Chemical Weapons (OPCW). The CWC is a far-reaching arms control treaty that prohibits the use, development, production, and transfer of chemical weapons. A core obligation for the 193 States Parties to the CWC is the verified destruction of all existing chemical weapon stockpiles.