HCN, or my nose says I'm dead

Question

As you see, I still post...

I studied chemisty decades ago (and when I was through with all the compulsory practica, I was sent to a computer chemistry workgroup and politely suggested to never touch a beaker again, which I happily followed and made my PhD there, otherwise probably the chemistry dept. of the university of Hamburg would no longer exist :-)

Here's one of my specialities as a walking disaster area. Hmmm, "Trennungsgang" seems to be nonexistent in English, make that Qualitative Inorganic Analysis. Don't ask me to remember the details, but Fe3+ is detected with NCS-. For another cation later you need H2O2. I never learnt to use a different test tube. The result were always the same - a geysir shooting out of the test tube and over my fingers (now that you say it, gloves exist) accompanied with some almond stink that suggests I just got a deadly dose of cyanide.

I'm remarkably hard to kill but methinks I rather misinterpreted the perceptions. So, maybe it only was less toxic HSCN that blew off? (I think the H2O2 solution was acidic.) BTW, Wiki says "odor pungent".

Answer 1

From the Toxic Substance Portal of ATSDR, "The [almond] odor of hydrogen cyanide is detectable at 2-10 ppm (OSHA PEL = 10 ppm), but does not provide adequate warning of hazardous concentrations. Perception of the odor is a genetic trait (20% to 40% of the general population cannot detect hydrogen cyanide)." However, from that same source, the NIOSH IDLH (immediately dangerous to life or health) is 50 ppm, so if your among the ~70% who can smell $\ce{HCN}$, you could note an odor and have a safety factor of ~10 before immediate death occurs. Of course, the smell is less noticeable as the sense of smell fatigues, and long term effects are another question.

As to whether you smelled thiocyanic acid, $\ce{HSCN}$, its odor is described as "pungent", not at all like bitter almonds, so likely that was not what you smelled. Thiocyanates are about 100 times less toxic than similar cyanides, and are even used internally in medicine.

The toxicity of $\ce{HCN}$ is roughly comparable to that of $\ce{H2S}$, which is frequently encountered in the lab and in nature, such as at geothermal features, but since most people can sense $\ce{H2S}$ at 0.03 ppm, it is treated far more casually.

But $\ce{HCN}$ is toxic enough that the old joke still applies. Question: "What's the difference between cyanide and sayonara?" Answer: "Sayonara means goodbye in Japanese, and cyanide means goodbye in any language."