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June 30, 2010
How Not To Do It: Hydrogen Gas Mixtures
Culturing bacteria is usually a pretty quiet affair. Bacteria aren't too noisy, and the equipment used to keep them happy isn't too dangerous. But there are exceptions. If you're going to culture anaerobes, you need somewhat more advanced technique, what with all that oxygen-is-deadly business. A professional-grade culture chamber for those beasts is usually filled with a mixture of about 80% nitrogen, 10% carbon dioxide, and 10% hydrogen. And those you'll be getting from three compressed gas cylinders, which is how they were doing it in a lab at the University of Missouri until Monday afternoon. . .
Well, regular readers will be expecting this to be a story of someone who did not remember to Treat Compressed Gases With Respect, but that's not the case. No, this is what happens when you don't Treat Hydrogen With Respect - and everyone in the audience who's had a hydrogenation reaction get frisky on them will be nodding their head in agreement at that thought. Somehow, enough hydrogen and enough oxygen got together around an anaerobic culture hood, and the mixture found an ignition source, and well. . .
Problem is, just about any hydrogen/air mixture will do. Anything from about 4% hydrogen in air to about 75% will ignite, and everything except the two ends of that range will go ahead and explode if given the chance. (Only acetylene is worse in that regard). And it doesn't take much to set it off, either, which is the other nasty thing about working with hydrogen. A static-electricity spark is plenty, as are the sparks generated by electrical switch contacts and the like.
As you can see, the lab was not improved by the resulting explosion. The latest report I have is that four people were injured, one seriously enough to still be in the hospital, although their condition has been upgraded to "good".
Initial reports were that this was due to human error, although everyone seems to be backing off that judgment until an official investigation is finished. At any rate, the local fire department stated Monday night that the problem was one or more people in the lab "not being familiar with the warning systems designed to alert them when the hydrogen level was approaching explosive limits (and) the gas was left on". If that was the case, then. . .you ignore a hydrogen level alarm at your peril. And here are seventeen blown-out windows, four people who are lucky not to have been killed, and one demolished lab as evidence.
Update: I had a link up to a commercial anaerobic culture chamber for illustration, but (as the manufacturer points out) these use cylinders of premixed gas with only 5% hydrogen which obviates this very problem. I thought it best to take down the link so that no confusion results - after all, it wasn't the model that was being used in this incident (and in fact would have avoided it completely). I should add that the email I received about this out was exactly the sort of courteous and informative request I have no problem responding to, as opposed to some others that have come in over the years.
(Photos are courtesy of the Missourian and the Columbia Fire Department).
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