A sign on the wall of firm that uses cyanide gas in the manufacturing process, "If you're smelling almonds, you're already dead". Exposure to cyanide gas must be avoided.
These agents act by binding the iron (FE) component of the cytochrome c oxidase system, which controls the cellular respiration and exchange of oxygen. The treatment of this agent includes the administration of oxygen and nitrates. Standard military treatment includes administration of 10cc of 3% solution of Sodium nitrate followed by sodium thiosulfate (50cc of 25% solution) by intravenous. Some other medical authorities recommend the use of Amyal Nitrate crushable ampules followed by the nitrates listed above.
Not true about the "if you're smelling almonds, you're already dead".
Way back in high school, one of my hobbies was collecting insects. At that time a common way to dispatch them after they were caught (without damaging them) was to put them into a "killing jar".
I made mine the classic way -- I got a tall glass coffee jar (the kind instant coffee comes in), and put an inch of potassium cyanide in the bottom, covered by an inch of sawdust, then an inch of plaster of paris (which is porous enough to let the fumes seep into the upper portion of the jar).
Aside: I got the potassium cyanide by asking my science teacher for some from the school chem lab supplies. He gave me the whole bottle and told me to bring back what I didn't use. Imagine that happening today.
I killed many insects in it (they died within 20 seconds, even with an insect's slow respiratory process), and it was still deadly after a couple of years of use. While using it I often got a good whiff of the contents myself. I "smelled almonds" many times, but I'm still here.
Today killing jars are usually made with ethyl acetate (nail polish remover) instead of cyanide, and have to be recharged every few weeks.