Asphyxiants are gaseous poisons, which produce respiratory embarrassment, leading to asphyxia. These gaseous poisons are basically four types: (i) Chemical asphyxiants: Chemical asphyxiants reduce the body’s ability to absorb, transport, or utilize inhaled oxygen. (ii) Simple asphyxiants: Simple asphyxiants are inert gases and they deprive tissue of oxygen by their ability to displace oxygen. (iii) Respiratory irritant asphyxiants: Respiratory or pulmonary asphyxiants are gases, which can damage the respiratory tract by destroying the integrity of mucosal barrier and produce non-cardiogenic pulmonary oedema, which impairs the oxygen diffusion across the alveolar membrane. (iv) Systemic asphyxiants: These are gases, which produce significant systemic toxicity by specialized mechanisms. Examples include: Carbon monoxide, cyanide, and smoke.