Via the New York Times:
Four Texas workers died and a fifth was hospitalized Saturday morning after a hazardous gas leak at a DuPont chemical plant east of Houston.
The workers were overcome about 4 a.m. Central Standard Time, apparently as they were responding to the leak of the gas, methyl mercaptan, according to the plant’s manager, Randall Clements.
Methyl mercaptan is mixed with odorless natural gas to give it its characteristic rotten-egg smell. The company said the leak was contained at about 6 a.m. The worker who was not seriously injured was being hospitalized overnight for observation.
The leak spread a stench across broad areas of La Porte, an industrial town on the Gulf of Mexico about 20 miles east of Houston, but the company said it posed no hazard to the community.
A spokesman for the U.S. Chemical Safety Board, an independent agency, said a team of experts would arrive in La Porte on Sunday to search for the cause of the accident.
Mr. Clements said in a written statement that the company was cooperating with federal, state and local authorities, and was conducting its own inquiry into the accident. “We will share what we learn with the relevant authorities,” he said in a statement.
...The company said that the leak began when a valve on a container of methyl mercaptan malfunctioned. La Porte’s emergency management coordinator, Jeff Suggs, said the accident occurred in an operating unit that produces additives for fertilizers....Questions that I have:
- I wasn't aware of methyl mercaptan/methanethiol's ability to be an acute toxin -- is it one? (Apparently so, according to this CDC report of a worker who died of exposure.)
- What happened here? I know there was a faulty valve - what happened to the workers? Was it a low-oxygen environment?
I'll be monitoring the story...
Methanethiol is actually quite toxic. I found LC50 = 650 mg/m^3 in mice and IDLH = 150 ppm (P. Patnaik “A Comprehensive Guide to the Hazardous…” 3Ed, 2007). IDLH stands for Immediately Dangerous to Life or Health.
ReplyDeleteTo compare the inhalation hazard to other gases the IDLH values are HCN 50ppm, H2S 100 ppm, NH3 300 ppm.
At high concentrations methanethiol causes death by respiratory paralysis and cyanosis.
The boiling point is 6°C and the vapor is heavier than air. I looked at the weather conditions in La Porte, TX at 4 am on Saturday (the time the release started). At the nearby Ellington Field, TX The Weather Underground reported 4.5°C and mild wind speed at 8.1 mph. My guess is that the methanethiol was stored as a liquid and when spilled it formed a dense, slow moving vapor cloud.
The workers who perished probably didn’t have much chance to escape. I fervently hope I am wrong here, but the prospects of the fifth victim are also grim. Victims of severe poisoning develop acute hemolytic anemia and methemoglobinemia, from which recovery is difficult.
Without a tremendous amount of research, Patty's Toxicology (1981) has LC50 (mice) at 1664 ppm (3278 mg/m3) and near-instant coma-inducing effects (mice) at 10000 ppm. Reaching 10000 ppm in a release is, conceivably, quite easy.
ReplyDeleteAs with all chemicals and toxicity - it's the dose that makes the poison.
And if memory serves, the production process utilizes hydrogen sulfide. H2S is really nasty -- we had a release at a nearby oil refinery years ago and it took several lives. Nearly got some of the responding paramedics as well. Was it a production accident or a storage accident? The media doesn't give much specific information, as usual.
ReplyDeleteAnother jobs for the CSB.
I'm confused. The article at http://www.chron.com/neighborhood/bayarea/news/article/La-Porte-plant-accident-causes-weird-smell-over-5895202.php clearly says that the CH3SH was used for as a feedstock to make insecticides and fungicides. So why are you mentioning the fact that elsewhere, it might be used as a scent in natural gas. That is also the case in the NYT article.
ReplyDeletePresumably, calling out the fact that MeSH is commonly used as an odorant is to give a casual reader a frame of reference. That reference will resonate the the general public much more than only stating that it is used as a feedstock for insecticides and fungicides.
DeleteIIRC, MeSH is used to produce methomyl (DuPont's Lannate insecticide).
DeleteMy late father was an entomologist involved in the development of Lannate (he brought Lannate from primary screening to product).
Umm... because CJ's quoting the NYT article?
DeleteYeah, otherwise it's just another random chemical the readership largely won't understand anything about. If anything, this actually helps AGAINST chemophobia because it's not just "this is a chemical and it's so toxic and you don't know anything about it other than it goes into things that kill fungi and insects".
DeleteFunny though, I thought they used tBuSH rather than MeSH. The lab definitely smelt of gas when I used tBuSH in an inefficient fume hood.
Cyanosis, respiratory paralysis... It sounds as if the toxicological effects are similar to those of hydrogen sulfide.
ReplyDeleteDDTea
In the late 70s during a hiatus from graduate school I briefly worked for a smaller chemical company that has since been gobbled up once or twice and is now part of a large company. One day I was instructed to test a ridiculous idea that elemental sulfur was contaminating the companies methane thiol product. I was specifically told to go out into the plant and sample about a liter of liquified profit using a pressure vessel I was provided with. I had a hard hat as my only protective gear. I received no training. I screwed up manipulating the valves and sprayed liquid methane thiol all I ver my arm. I got a good snort of it before I got the valve shut down, I didn't tell anybody, because that would not have played well. The subsequent experient, dictated by the lab director, involved slowly venting the entire liter through a glass tube packed with glass wool and out the exhaust of a lab fume hood.
ReplyDeleteAny chance they died of suffocation? We know from NMR safety training that a leak of a gaseous compound that will displace the oxygen will quickly kill people in the room.
ReplyDeleteThey probably died of suffocation, but it was most likely caused by respiratory paralysis and methemoglobinemia/cyanosis. That means they couldn't get air into their lungs and even if they could their blood couldn't transport the usual amount of oxygen.
DeleteWhen an NMR magnet quenches and helium boils off it dilutes air. The reason for suffocation is physical, i.e. not enough O2 to breathe.
sympathy for anyone (and their families) who dies in an industrial accident...but I hope there's a special place in heaven for people who die at the hands of a malordorous compound like methanethiol...wow, what a terrible way to go!
ReplyDeleteAnything in high enough concentration is going to be deadly.
ReplyDeleteWhat kind of Herbicides and Insecticides did they make at that Dupont facility?
ReplyDelete