Lethal Doses of Chemical Agent

Median Lethal Dosage (LCt₅₀) - The Median lethal dosage of a chemical agent employed for inhalation as a vapor or aerosol is generally expressed as the LCt₅₀. The LCt₅₀ of a chemical agent is the dosage (vapor concentration of the agent multiplied by the time of exposure) that is lethal to 50 percent of the exposed individuals. Dosage of chemical agents inhaled into the lungs are usually expressed in milligrams-minute per cubic meter of air breathed (mg-min/m³). If 100 people are exposed to a concentration of the Nerve agent VX, equal to 15 milligrams per cubic meter of air, it is statistically probable that half of them will die if the exposure time is as long as a minute. The 50 percent dividing line concerning life and death is related to the fact that people enjoy different health, either because of age, diet, sex, or disease while another important controlling factor would be attributed to the rate of inhalation (i.e., an individual exposed during some physical effort of fatigue which increases the rate of inhalation, e.g., running), internal efficiency of the body's blood, organs, tissues and state of mind.

Toxic Chemical Agents

Chocking Agents

Chocking agents injure an unprotected person chiefly in the respiratory tract, i.e., in the nose, throat, and, particularly, the lungs. In extreme cases membranes swell, lungs become filled with liquid, and death results from lack of oxygen; thus these agents "choke" an unprotected person. Fatalities of this type are referred to as "dry-land drowning".
• Phosgene (CG) - Normally a chemical agent with a short agent cloud duration. Used extensively in World War I: in fact more than 80 percent of World War I chemical fatalities were caused by CG.
• Diphosgene (DP) - DP has a much higher boiling point that CG and it is slightly lachrymatory. It is converted to CG in the body and exerts its effect after this conversion.

Nerve Agents

• Tabun (GA)[1] - A colorless to brownish liquid giving a colorless vapor.
Eye effect - Very high toxicity; much greater through eye that through skin. Vapor causes pupil of eye to contract, resulting in difficulty in seeing in dim light.
Skin effect - LDt₅₀ (liquid), 1-1.5 g/man. Liquid decontamination of smallest drop is essential. Vapor penetrates skin readily. Skin LCt₅₀of vapor is not known - probably between between 20,000 and 40,000 mg-min/m³.
Physiological Symptoms - Individuals poisoned by nerve agents display the following symptoms: difficulty in breathing: drooling and excessive sweating; nausea, vomiting, cramps and involuntary defecation and urination; twitching, jerking and staggering; headache, confusion, drowsiness, coma, and convulsion; and, when the agent is inhaled, dimness of vision and pinpointing of the eye pupils. However, if the exposure has been cutaneous or by ingestion of a nerve agent, the pupils may be normal or, in the presence of severe systemic symptoms, slightly to moderately reduced in size. In this event, the symptoms of nerve agent poisoning other than its effect on the pupils must be relied upon to establish a diagnosis. These nerve agent symptoms are followed by cessation of breathing and death. Symptoms appear much more slowly from skin dosage. Although skin absorption great enough to cause death may occur in 1 to 2 minutes, death may be delayed for 1 to 2 hours. Respiratory lethal doses kill in 1 to 10 minutes, and liquid in the eye kills nearly as rapidly. The number and severity of symptoms are dependent on the quantity and rate of entry of the nerve agent into the body (very small skin dosages sometimes cause local sweating and tremors with little other effect).

[1] The first known nerve agent, synthesized by German chemists in 1936; a highly toxic combustible liquid that is soluble in organic solvents and is used as a nerve gas in chemical warfare .