First of all, I hope you're asking this question purely from intellectual curiosity. Secondly, let me say immediate treatment is absolutely essential. <a href="http://atsdr1.atsdr.cdc.gov:8080/tfacts8.html" target="_top">Cyanide poisoning</a> usually kills people in less than 15 minutes.

Cyanide is commonly thought of as a gas, but you also can be poisoned by it if you ingest wild cherry syrup, prussic acid, bitter almond oil, or large amounts of apricot pits. Cherry seeds, peach and plum pits, corn, chickpeas, cashews, and some other fruits and vegetables contain cyanogenic (i.e., cyanide-forming) glycosides that release hydrogen cyanide when chewed or digested. However, cyanide poisoning from a food source is rare.

The first symptoms of cyanide poisoning are rapid heartbeat, headache, and drowsiness - followed by coma, convulsions, and death (at which point the face is usually bright red as a result of a change in hemoglobin, when cyanide binds with it in the blood and prevents the use of oxygen by cells).


Here's the good: You can <a href="http://atsdr1.atsdr.cdc.gov:8080/ToxProfiles/phs8812.html" target="_top">survive mild doses</a> of cyanide. The way to <a href="http://www.healthworld.com/LIBRARY/Books/Healthyself/firstaidpoison.htm" target="_top">treat cyanide poisoning</a> is to undo that binding process and free up the oxygen for cells to use. You need to remove the affected person from the source of the cyanide immediately. Induce vomiting if possible, or wash the stomach with a saline solution. Then give, of all things, poppers. Amyl nitrite is a specific antidote. You could give an intravenous infusion of sodium nitrite, followed by an infusion of sodium thiosulfate. You also might give 100 percent oxygen to support respiration. If symptoms recur, you repeat the process.

HCN is thought to have been one of the small molecules in the Earth's primeval atmosphere and to have been an important source or intermediate in the formation of biologically important chemicals.  For example, under pressure and with traces of water and ammonia, HCN produces adenine, one of the essential amino acids essential for life..  HCN can also act as a condensing agent to turn amino acids into polypeptides.

Important industrial uses of HCN are to make adiponirile which is then used to form nylon,  and as a fertiliser.  

It is evolved when metal cyanides such as NaCN or KCN are treated with acids.  It is made commercially on a large scale by the reaction:

CH4 + NH3   = (1200C, Pt catalyst) HCN + 3H2