What Are Chemical Weapons?

Chemical weapons are munitions, devices, and toxic chemicals designed to cause death or harm through the chemical action of the substance on biological processes, and the practice of using them is called chemical warfare. Under international law the definition is deliberately broad: it covers the toxic chemical itself, the precursors used to make it, the munition designed to deliver it, and any equipment specifically built for its use. That breadth exists because the distinction between a legitimate industrial chemical and a weapon lies in purpose and quantity rather than in molecular structure, a problem the treaty regime calls the general purpose criterion.

Large-scale use dates to the First World War, when chlorine, phosgene, and sulfur mustard were released on the Western Front, and the reaction to that experience produced the 1925 Geneva Protocol banning use but not production or stockpiling. The gap was closed by the Chemical Weapons Convention, which entered into force in 1997 and is administered by the Organisation for the Prohibition of Chemical Weapons. The Convention text and its implementing structure prohibit development, production, stockpiling, transfer, and use, and require the destruction of declared stockpiles under international verification.

Agent Classes and Mechanisms

Agents are grouped by physiological effect. Nerve agents, including the G-series compounds sarin, tabun, and soman, the more persistent VX, and the Novichok family, are organophosphorus compounds that inhibit acetylcholinesterase, allowing acetylcholine to accumulate at synapses and producing convulsions and respiratory failure within minutes. Vesicants such as sulfur mustard and lewisite alkylate DNA and proteins, causing blistering of skin, eyes, and airways with a characteristic delayed onset. Pulmonary agents including chlorine and phosgene damage the alveolar membrane and cause fluid accumulation in the lungs, while cyanide compounds block cellular respiration at cytochrome c oxidase. Riot control agents and incapacitants form a separate legal category, permitted for domestic law enforcement but prohibited as a method of warfare. The CDC chemical emergency fact sheets document the exposure routes, clinical signs, and treatment protocols associated with each class.

Detection, Protection, and Decontamination

Field detection has to identify trace quantities of a toxic vapor quickly and with few false alarms, and the dominant deployed technology is ion mobility spectrometry, which separates ionized molecules by their drift velocity in an electric field at ambient pressure. Surface acoustic wave sensors, flame photometric detectors, and portable gas chromatography coupled to mass spectrometry supplement it, and standoff detection uses passive infrared spectrometry to identify vapor clouds at a distance. Research continues on lower-cost selective materials, including two-dimensional carbides evaluated as nanosensors for selected chemical warfare agents. Protection relies on activated-carbon filtration in respirators and collective protection systems, and on impermeable or selectively permeable suits. Decontamination uses alkaline hydrolysis, oxidative chemistry such as hypochlorite solutions, and catalytic destruction, with medical countermeasures centered on atropine, oximes, and anticonvulsants for nerve agent exposure.

Verification and Destruction

Verification is what distinguishes the current regime from earlier agreements. States parties declare stockpiles, production facilities, and relevant industrial plants, and OPCW inspectors carry out routine inspections of declared sites plus challenge inspections on request. Analytical work relies on a network of designated laboratories operating to strict chain-of-custody rules, with identification based on matching mass spectra and retention data against a central analytical database. Destruction of declared stockpiles is carried out by high-temperature incineration or by neutralization followed by biotreatment or supercritical water oxidation, chosen partly because incineration draws public opposition near destruction sites. Investigations into alleged use, including work in Syria, combine environmental sampling, biomedical samples, and munition remnant analysis.

Applications

Work on chemical weapons defense and disarmament draws on a range of technical fields, including:

• Analytical chemistry and mass spectrometry
• Chemical sensor and detector engineering
• Hyperspectral and infrared standoff imaging
• Toxicology and medical countermeasure development
• Protective materials and filtration engineering
• Hazardous waste destruction and process safety
• Arms control verification and treaty compliance monitoring