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How Not to Do It

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. . .
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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.
062810_InsideExplosion_1_t_w600_h1200
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).
Missou explosion exterior,jpg

21 comments on “How Not To Do It: Hydrogen Gas Mixtures”

  1. Jesse says:

    Does this mean we should think twice before moving to hydrogen-based power sources? Should we expect to see the occasional horrific explosion from our new amazing fuel cell based cars?

  2. processchemist says:

    Hydrogen detectors are quite cheap and reliable. In case of leaks, the low density of the gas makes hard to obtain dangerous concetrations in a properly ventilated environment. But usually biologists don’t have a proper instruction about chemical safety.
    There are gases and vapours that makes me more nervous than hydrogen: diethyl ether, hexane, propane, butane, acetylene.

  3. drozzy says:

    I don’t think it has anything to do with human-error, but rather the poor design of the warning system itself.
    The state of the system should have been clearly visible. I bet the indicators were somewhere behind a corner in a closet.

  4. Mark says:

    I’ll bet there were some bleeding eardrums as a result.
    Mark

  5. fuelcelldave says:

    On the subject of Hydrogen cars the attached report is quite interesting in comparing with what we have now
    http://evworld.com/library/swainh2vgasVideo.pdf

  6. RB Woodweird says:

    I am going to shamelessly cut and paste from a previous post of mine:
    …our PI had a small lab (maybe 8 by 12) right next to his small office. In that lab we had our Parr shaker set up. I went in on a Friday morning and noticed that someone had put in a fresh tank of H2, pressured up and ready to go. On Monday morning I took in my reaction to run. The tank was empty. It had bled out during the weekend, when the PI was busy at his desk not six feet away on the other side of a wooden door. Good thing he was not a smoker.

  7. Virgil says:

    IIRC, the H2 in these anoxic systems is used with a palladium catalyst, to scavenge O2 and reduce it to H2O. The system (if designed properly) regulates and delivers H2 only when the O2 level climbs above a certain level and requires scavenging. Usually the problems arise with the catalyst needing replacement, or the inlet-pressure on the regulator being set too high so it over-powers the solenoid valve that controls the flow.

  8. Dave says:

    There are quite a few groups around the world that perform high altitude ballooning. Most of these groups use Helium to inflate their balloons, but some are switching to Hydrogen, due to its MUCH lower cost (and, the slight additional lift doesn’t hurt either). However, there is considerable concern over the “Hindenburg effect”. Fortunately, most of the large balloons are filled outdoors, so any leaking Hydrogen can dissipate relatively quickly. That still doesn’t mean that there isn’t a bit of excitement when the initial bit of Hydrogen flows through the pipe and ignites with the residual atmospheric Oxygen in the pipe due to the static produced by it flowing.
    http://en.wikipedia.org/wiki/ARHAB
    Dave

  9. processchemist says:

    IMHO, using H2 and a Pd catalyst as oxigen scavenger has an intrinsic level of danger. What happens if suddenly a fair amount of air breaks in the system?
    I mean, adsorption is an exhotermic process, and many that tried to put dry Pd/C in methanol had a direct experience of this thermodynamic fact. Oxidations are exhotermic reactions. So in this case, the catalyst, if working, should be hot: a perfect ignition tool.

  10. Tc King says:

    Where there is an accident there is always blatant negligence. Look at the solvent carboy next to the bombed out mass spec. nOTICE ANYTHING WRONG MY FELLOW SCIENTISTS?
    Naughty! Naughty! Bad Scientist!
    Release the Lawyers!

  11. Curt Fischer says:

    Many microbiology labs that use Pd catalysts for O2 scavenging use hydrogen that is supplied as a 5% mixture in nitrogen. That way, any accidental mixing of the H2-containing gas with air will dilute the H2 concentration to below what’s needed for flammability or explosivity.
    I’m not sure why this lab couldn’t do the same.

  12. newnickname says:

    1980-something. A corner of a building in Kansas or Kentucky was blown apart when the group was preparing 100% H2O2 (it’s a lit prep). I wish I could remember more details more accurately.
    “Old school” practice was to “crack” the main valve on a new cylinder of gas (N2, etc.) to blow out dust and grit before affixing the regulator. (Today, valves are plastic wrapped and clean upon arrival.) Except NEVER crack the valve on a hydrogen cylinder. Most gases cool upon such rapid expansion; H2 (and a few others) HEAT upon Joule-Thompson expansion with possible explosive repercussions.

  13. TFox says:

    The anerobic chamber I’ve used is supplied from a cylinder of trigas mix, I think it’s 7 or 10% H2, some CO2 and the rest N2. I understand that the composition was selected so that no possible mix with room air could be explosive, which improves the safety quite a bit. You only need 1-2% H2 in the chamber to scavenge O2, so having a cylinder of 100% H2 around seems like a pointless and easily avoided risk.

  14. Mike Lee says:

    An on demand Hydrogen generator is a good idea for applications such as this. Storing H2 in a cylinders should be avoided. Even a gas mixture with low levels of H2 are labeled “Flammable” for a reason. I usually recommend a H2 generator with the ambient gas delivered as required to complete the blend. H2 generators store no product. It is a demand system where the product is used as it is produced.

  15. Tom Viviano says:

    Hydrogen Generators are the way to go in this case. Because they don’t store large amounts of gas and it is under 100psig. This makes the system intrinsically safe, you can’t reach the 4% concentration for LEL. If a cylinder goes you can see the results I’ve work for the Parker/
    Balston. We are the global leader in Gas Generators specifically Hydrogen

  16. Jack says:

    Glad to hear nobody was seriously hurt. I agree with the above comments regarding Hydrogen Generators for this application…systems include overflow/leak detections which automatically shut them off if demand exceeds system capacity…at low flow and low pressure, 4% in the room is not possible.

  17. Kim says:

    Can a generator produce enough gas to achieve a 4% concentration?

  18. Sharon says:

    It’s nice that nobody was seriously injured.
    Lack of knowledge in safety measures is a fatal human error, maybe now they will start to get familiar with the warning systems.
    After all familiarity with the things we used is a good precaution!

  19. Anonymous says:

    Was that house an example of the what this experiment does?

  20. Shyam Kumar says:

    Hi,
    I want to mix H2/CH4/N2 at a ratio of 500 sccm/10 sccm/2 sccm at a temperature of chamber 900 deg Is It be the safe to use this mixture?

  21. Anonymous says:

    The “Respect” link in the second paragraph and the “worse” link in the third paragraph need updating.

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