Burning of nitrogen-containing polymers (plastics, wool, silk)
Gaseous chemical weapon known as prussic acid, hydrogen<unk> , or hydrocyanic acid
Prolonged use of nitroprusside
Pits of peaches, pears, apricots, crab apples
Intentional poisoning
Binds to cytochrome oxidase in mitochondria; leads to cessation of electron transport
Causes switch from aerobic to anaerobic metabolism despite adequate O2
Causes switch from aerobic to anaerobic metabolism despite adequate O2
Paris Fire Brigade protocol recommend hydroxocobalamin administration patients who have had known smoke inhalation in an enclosed space with any of the following:
Cyanide toxicity
Blister chemical agents 
Chlorate toxicity
Lewisite 
Sulfhemoglobinemia
Sulfur mustard 
Methemoglobinemia
Phosgene oxime 