The toxicity of simple asphyxiants, chemical asphyxiants, common irritant gases and other gases which have both local and systemic effects was reviewed and discussed. Studies have indicated that asphyxiation is most likely to occur during exposure to gases in confined spaces. Simple asphyxiants include colorless, odorless gases such as nitrogen (7727379), helium (7440597), argon (7440371) and methane (74828). Occupational exposure to these gases can occur in welding, through food preservatives, in fuel and industrial processes. Acute asphyxia from gas exposure occurs in four stages and results in immediate unconsciousness followed by death. The effect of prolonged exposure to carbon-dioxide (124389) (CO2) is related to its effect upon oxygen levels; CO2 may be tolerated if oxygen is maintained above 21%. Carbon-monoxide (630080), often produced when organic materials are heated with low oxygen, is a chemical asphyxiant which affects hemoglobin and decreases oxygen transport within the body. Hydrogen-cyanide (74908), also a chemical asphyxiant, targets the enzyme cytochrome-c-oxidase in the respiratory cycle, inhibiting electron transport and preventing cellular use of oxygen. Ammonia (7664417), chlorine (7782505), sulfur oxides, ozone (10028156), nitrogen oxides, and phosgene (75445) are classified as irritant gases. Exposure to these will affect the pulmonary region of the lungs and may cause increased airway hyperactivity. Other gases such as formaldehyde (50000) and ethylene-oxide (75218) were also discussed.