(Chem) A colorless, tasteless, and odorless gas, CO, mol wt 28. 01, mp -200 to -205^oC, bp -191. 5^oC. CO is produced during incomplete combustion of a carbona ceous fuel. Mixtures of CO, H2, N2 are common fuels called town gas, prod ucer gas, etc. CO + 0 with traces of water are explosive, and reaction of the gas with chlorine forms deadly phosgene. Syn: Sweet Damp; white damp. See: Damp. Note: The gas is extremely toxic, not because of actual damage to body tissues, but because it has a strong affinity for the hemoglobin in the blood, displacing oxygen and causing anoxia in the body tissues, esp the brain. The process is reversible: hemoglobin freed from CO (e. g. , by oxygen resuscitation) recovers its oxygen-carrying capacity. Ordinary gas masks afford no protection against CO, and special breathing apparatus should be used. Symptoms of "CO-poisoning" are blurred vision, headache, nausea, dizziness, and finally loss of consciousness. Without protection, 50 ppm (0. 005 by volume) is the threshold limit value for prolonged exposure. Concentrations of 1000 ppm (0. 1%) can be fatal within 1-hour. See: Carboxyhemoglobin. First-Aid Treatment requires removal of the casualty from the CO atmosphere, administration of oxygen, and absolute rest