» Jump To: Chlorine — Phosgene — Diphosgene
Choking are heavier gases that create fluid buildup in lungs and cause death from lack of oxygen. They cause inflammation of the lung tissue. As a result, large quantities of fluid from the bloodstream enter the lungs, causing pulmonary edema. Victims of choking agents "drown" in from their own bodily fluids. Choking agents are also known as pulmonary agents.
Chlorine is a poisonous yellowish green gas. It is a member of the reactive halogen group on the periodic table and exists in nature as a diatomic molecule (Cl2).
Chlorine causes the lungs to fill with fluid and the victim literally drowns from the inside. It iritates respiratory systems especially in young and ederly people. In its gaseous state, it irritates mucuous membranes. In its liquid state, it burns skin tissue. A dosage of 1000 parts per million is required to kill a person.
The recommended exposure to this gas is less than 0.5ppm. Non-lethal exposure to chlorine gas can result in pulmonary edema, or fluid in the lungs. Prolonged exposure to chlorine increases susceptibility to other lung diseases.
Chlorine gas was employed by the Germans in World War I, where a total of 93,800 tons of chlorine was produced by all nations.
Engineers at I.G. Farben, the German chemical giant, developed a way to produce vast amounts of chlorine gas, pack the liquid gas in cylinders, and release it from the trenches. This was the second major scientific victory for Farben and Fermany's leading chemist, Fritz Haber of the Kaiser Wilhelm Institute. Earlier, they had invented a way to extract nitrogen gas from the air because the British Navy had cut off Chilean nitrate trade with Germany.
Nowadays, second-year high school students produce small amounts of toxic chlorine gas in school labs.
Phosgene is a colorless gas that smells like newly-mown hay and chokes its victims much more quickly than chlorine. It exists as a non-flammable gas or a refridgerated liquid.
Phosgene exposure usually has no initial symptoms and thus early detection is difficult. Symptoms usually appear within 24 hours but can take up to 72 hours to manifest.
In the tissues of the respiratory tract, phogene gas combines with water to form carbon dioxide (CO2) and hydrochloric acid (HCl) - see the simplified chemical equation below. The HCl acid then dissolves the membranes in the lungs. Fluid fills the lungs, and death results from blood loss, shock, and respiratory failure.
Simplified chemical equation for the phosgene reaction in the lungs: COCl4 + H2O --> CO2 + HCl
Phogene was first created by John Davy in 1812 using sunlight on a mixture of carbon monoxide and chlorine. In World War I, 36,600 tons of phosgene were produced out of a total of 190,000 tons for all chemical weapons. It was responsible for 85% of the 100,000 deaths caused by chemical weapons.
Nowadays, phogene is a major industrial chemical with approximately 2 million tons produced every year for the manufacture of plastics, herbicides, pesticides, and dyes.
In the military, phosgene is referred to as CG.
People can be exposed to phosgene through skin contact or eye contact. They can also inhale it by breathing air that contains phosgene. If phosgene liquid comes into contact with food, the contaminated food can be a source of phosgene exposure.
In large industrial chemical plants, phosgene is produced by passing purified carbon monoxide (CO) and chlorine gas (Cl2) through a bed of highly porous carbon, which acts as a catalyst in the reaction. The chemical equation for the production of phosgene is:
CO + Cl2 --> COCl2
The reaction is exothermic, meaning heat is produced in the process. The reaction chamber must be continuously cooled to carry away the heat it produces. The reaction is usually carried out between 50°C and 150°C. If the temperature exceeds 200°C, phosgene decomposes back into carbon monoxide and chlorine.
Phosgene is a Schedule 3 gas under the Chemical Weapons Convention. As such, all production sites producing more than 30 tons per year must be declared to the OPCW.
Diphosgene (DP) was developed during World War I a few months after the first use of phosgene. At standard temperature and pressure (STP) it is a stable colorless liquid. If the temperature is raised to 300°C, diphosgne decomposes to phosgene.
Diphosgene is produced by radical chlorination of methyl formate or methyl chloroformate (chloroform) under UV radiation. Its vapor is a lung irritant and kills 100% of all test rabbits at a concentration of 0.9mg/L in air.
Since it is a liquid at room temperature, it is safer to handle and easier to measure than phosgene gas. Because of this, it has replaced phosgene in the laboratory. DP must be transported in glass (not metal) containers.
Diphosgene is believed to react directly upon the walls of the alveoli and capillaries in the lungs. Clinically, it behaves like phosgene (see above). In the presence of water, DP breaks down into hydrochloric acid and carbon dioxide. DP is heavier than air and remains in low-lying spaces for prolonged periods. Thus, children are at an increased risk for diphosgene exposure. DP is not detoxified in the body, so exposure is cumulative. Respiratory effects occur at dosages of 1-10 ppm, with dosages greater than 25 ppm rapidly fatal.
Due to diphosgene's low water solubility, victims often inhale high amounts of DP vapor before symptoms appear.
The first use of disphosgene was in May 1916. It was used as a poisonous gas in German artillery shells during World War I. It was developed because, at the time, disphogene vapors could destroy the filters in gas masks. Nowadays, nerve agents have predominatly replaced diphosgene and other choking agents as the dominant chemical weapon.
Sources:
Chapter 34, p161.