Thursday, September 20, 2012

Dirty Hood = Good Hood

Ever worked in a completely new chemical fume hood?

I have. Actually, due to moves and new facility construction, I've been (lucky?) to have three completely new hoods - hoods devoid of any smells, stains, or funny noises. All still had working baffles, legible installation labels, functioning flow meters, and bright white walls.

I ruined them all.

Chemjobber's latest post, referring to a "stinky walk-in hood," along with Pauling's lab notebooks got me thinking: How many times have I had to strip everything out of my hood, and start from scratch? I counted at least three; each one occurring in a beautiful, unsullied space.

In graduate school, I set up a sodium-mediated halogen exchange / rearrangement a few weeks after our move. After carefully flame-drying the apparatus, I greased and clamped all the joints, and set it to heat in an oil bath. I lowered the hood, and walked the ten feet or so to my desk...boom! We had a motley crew of older hot plates that didn't always heat up like you'd hope. Best I could piece together, there was an autoinitiation, followed by a massive exotherm I hadn't observed on smaller scale. Best part? After splattering my hood with compound, the flying glass cracked the oil bath, and little pieces of flaming sodium rained down around the pool of oil forming below my stir plate. Good times.
Total cleanup time: 3 days

As a postdoc, I had the "honor" of installing my own monkey bars, manifold, and otherwise arranging my virgin hood exactly as I pleased. Fast forward about a year, when I decided that a fairly exothermic borohydride reduction would go much better with a solid addition funnel. I'd covered all my bases - passive N2, massive cooling bath, flame-dried everything, the works! Except for one tiny variable: the borohydride particle size was too fine for the funnel's Teflon screw. One turn led to accidental addition of about half the reactant. Upon solution contact, the sudden gas release blew backwards into the solid addition funnel, which commenced to shoot a fine dust of borohydride onto every hood surface, including my arms.
Total cleanup time: 2 days

Later into my career, I had another heated reaction fail in stupendous fashion. The compound, a gummy orange solid, coated every surface of my hood: behind the sash, inside the light ballast, up the baffles, even down into the storage cabinets underneath. When I was finally done with that cleanup, my lab coat had been stained so thoroughly orange that we just bagged it and sent it out as waste.
Total cleanup time: 2 days

Look, all of these incidents would have been much worse if my sash had been up, or if I hadn't been wearing correct PPE when they occurred. We think about fume hoods as big vacuum boxes, but they're also great for containment of runaway reactions.

Readers: I know I'm not alone. Have a spectacular story of a reaction gone wrong? Share it in the comments.

3 comments:

  1. Thankfully I haven't had anything go spectacularly wrong (only a small fire from t-butylphosphine), but your post did remind me of an incident with another PhD student in my group.

    We had just got a new lab and he was purifying some poly(3-hexylthiophene) using soxhlet extraction. It bumped and shot up the condenser, even reaching the ceiling of the hood... it's still stained purple even after a lot of scrubbing! They sure don't stay clean long.

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  2. My fav from grad school was... In brilliance/unstoppable ego I decided that group cleanup was the right time to clean out the hexane still. now for a little background. The hexane was distilled to remove grease before running columns. we would store the hexane over CaH for reasons that escape me now. After more years than I care to guess, there was quite a bit of CaH/CaOH in the bottom of a 5 L round bottom. I started really carefully, first IPA, then EtOH. after an hour or so there was no more bubbling and i started to add ice (while in an ice bath. suddenly a hidden cash of CaH must have had its protective coating dissolve. the eruption coated the hood. I never could get at the light fixture at the top of the hood. When I left the lab years later there was still a coating on the ceiling of the hood.

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  3. Have a spectacular story of a reaction gone wrong? Share it in the comments.

    Milkshake has a few. He's a better storyteller though, so I won't steal his thunder.

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