DCHAS-L Archives, Sep 25 2015 - Re: [DCHAS-L] Pyrophorics

The old school "gold standard" method for testing the quality of a glove box atmosphere is to open a small vial of diethyl zinc. If the O2 concentration is higher than just a few PPM, it smokes rather considerably even though its BP is 117 C. If your box is supplied with liquid N2 gas packs (boil off) or 5 nines N2 cylinders (99.999%) you should be able to achieve a pristine atmosphere just by purging (into a hood) for a couple minutes. If you use a lower quality N2 you'd need to have a purifying dry train. My only concern for atmosphere would be in a glove bag rather than glove box.

I've seen some diakyl zincs smoke quite a bit, but never seen anything close to ignition in a dry box. Had a friction detonation once and a rotavap flask implode once, though.

Digressing just a bit, during my first month or two of grad school, the lab I was assigned to had quite a number of old and unlabeled reaction vials piled in beakers in the back of the hood. As I was complaining to one of my colleagues about the situation, I illustrated my point by picking up an unlabeled 30 mL vial that was 3/4 full with a clear liquid. There was a big wad of electrical tape around the cap and a nice white crust around the edges of the tape - the telltale sign of something fairly reactive that had come out of one our group's many glove boxes. At that moment, a piece of the crust fell off the side of the vial and a rather beautiful blue jet of flame about 2 inches long shot out for about 3 seconds before the jet crusted itself shut again. At least I had the presence of mind not to drop it.

We couldn't pump it back into the box to deal with it, I was generally unaware that EHS existed, and so my solution was to put the vial in the bottom of an ice bucket filled with dry ice and smash it with a pipe wrench. Then we let it die slowly in the back of the hood. It died quite peacefully. We later found that syringing old scuzzy nBuLi solutions onto crushed dry ice was a quick and effective way of quenching that as well, although I doubt you'll find this procedure in the (ahem) accepted safety literature.

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On Sep 25, 2015, at 12:03 PM, NEAL LANGERMAN <neal**At_Symbol_Here**CHEMICAL-SAFETY.COM> wrote:

All

Thank you for the initial response; you have confirmed what I noted… the data do not seem to be available.

Allow me to change the question…
Some facts:
The specification for oxygen in cylinder nitrogen is less than 200 ppmv and it goes down as the quality of the nitrogen goes up. Semiconductor grade is < 3 ppmv.

If you were monitoring the oxygen concentration inside a glove box (containment) using nitrogen as the purge gas, what would be the oxygen concentration at which you would say (IN YOUR WRITTEN SOP) that work with a pyrophor can begin.

It would be really helpful to have this answer documented with data; ideally peer-reviewed, but hard anecdotal - not just opinion - would be ok.

And, I really do not care about t-BuLi, but used it as an example. Again, I am trying to find support for pyrophor use which is analogous to hydrogen, where the data clearly support <5% being not ignitable no matter the hydrogen concentration.

Thank you for continuing this discussion

Neal

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**med.cornell.edu] On Behalf Of Melissa Charlton-Smith
Sent: Friday, September 25, 2015 6:45 AM
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Subject: Re: [DCHAS-L] Pyrophorics

Neal, are you speaking the common 1.5% to 1.7% solution in pentane? The LEL of pentane is 1.5% (10% LEL, 1,500 ppm) which doesn't really answer your question about t-BuLi itself. Like you I have searched and the best I could fine was how to isolate t-BuLi solutions to pure crystalline form, but it was never exposed to varying % of oxygen, all was done under argon and/or nitrogen.

Mel

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**med.cornell.edu] On Behalf Of NEAL LANGERMAN
Sent: Thursday, September 24, 2015 4:15 PM
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Subject: [DCHAS-L] Pyrophorics

Does anyone have any citations for the low limiting oxygen concentration of pyrophoric compounds. I am specifically looking for the oxygen percentage at which compounds such as t-BuLi become non-ignitable. For example, that value is 5% for hydrogen. I have found a reference for silane, but, as is typical for silane, there are a myriad of confounding issues.

I have searched both SciFinder and Science Direct and have not found helpful data.

Thanks

Neal

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