H2S ------ Sorry, Couldn't Think of Anything Snazzier

H₂S is a colorless gas with a rather distinctive smell. Its odor is often described as being similar to rotten eggs, but I cannot verify that personally because I've never come across a rotten egg. On the other hand, I have worked with H₂S off and on over the years, so I do know what it smells like. H₂S is quite poisonous, significantly more toxic than hydrogen cyanide, but due to our nose's ability to detect it at ppb levels, it's rarely deadly. Safety note: since your nose is quickly desensitized to H₂S, it can still be deadly if you aren't paying attention.

H₂S has been in the news lately, in a Jekyll and Hyde sort of way. Peter Ward, an expert on mass extinctions, has been discussing the role of H₂S in many of the known mass extinction events which appear periodically in the fossil record. The theory is that during times of global warming brought about by raising CO2 levels (usually as the result of massive volcanic activity), ocean circulation stops, which results in a huge drop in its oxygen content. This allows H₂S producing bacteria to take over the oceans, eventually choking off the oxygen and wiping out most of the planet's species.

Despite this rather negative press, other researchers are beginning to find that in small doses, H₂S can be beneficial when used to slow down the metabolism of mice. In one study, this technique is shown to be useful in minimizing the damage caused by heart attacks. In another study, H₂S is being used as a means of possibly inducing suspended animation.

Using H₂S to slow down a person's heart freaks me out a little, mostly because it almost killed my roommate in grad school. My roommate was performing a synthesis in a hood using an H₂S tank when, somehow, the regulator malfunctioned (or broke) during the reaction, venting gas directly into the hood. In order to shut it off, he had to hold his breath, raise the hood, and close the H₂S tank with a wrench. In hindsight, he should probably have just let the tank vent, but in the process of closing the tank he ended up taking a breath or two. He mentioned feeling a little woozy and I walked him out into the hall whereupon he collapsed onto the floor, unconscious. While someone else called the university emergency number, I stayed with him, although I wasn't exactly sure what I could do. His breathing started getting ragged, which scared me, but it was even scarier when his breathing appeared to stop. I tried giving him mouth to mouth resuscitation, but I had difficulty forcing air into his lungs because his teeth were tightly clenched. Fortunately, he regained consciousness about a minute or two later, just in time for the fire department to show up. We tried explaining to the firemen what had happened but they didn't really know what H₂S was and were more interested in finding a chemical spill onto which they pour sodium bicarbonate, which apparently was the sum total of their training. Eventually they noticed a red spot on my roommate's forehead, no doubt due to its hitting the floor earlier, and satisfied themselves with pouring baking soda on him, despite our assurances that it wasn't necessary.