Explosion proof has two meanings when applied to a hood.
The First, is, as Debbie explains, is a hood classified as either Class I Division 1 or Class 1 Division 2 (or the alternate Zone 0, 1, or 2). This is from NFPA 70 the National Electric Code and refers only to electrical equipment. And, as Debbie mentioned, as long as the light is sealed and outside the hood and the plugs are outside the hood, the interior MAY be considered Class I Division 1 or 2. To do either, all wiring inside the hood and all equipment must be approved for a Class I Division 1 or 2 area. If it is Division 1 then a Division 2 area may have to extend outside the hood into the lab. Usually you can avoid this with proper alarms and controls ensuring that the exhaust ventilation is always working properly and automatically shutting down all equipment inside the hood if it does not work properly or fails. You can look at Area Electrical Classification in Research Applications: Is It the Only Mitigative Choice? (Chemical Engineering, Feb, 2021), Install Ventilation to Reduce Area Electrical Classifications, (Chemical Engineering Progress, August, 2020), Ventilation Dilution: A Safe Way to Avoid A Fire or Explosion or a Placebo?, https://www.linkedin.com/pulse/ventilation-dilution-safe-way-avoid-fire-explosion-placebo-palluzi/, or Laboratory Area Electrical Classification, https://www.linkedin.com/pulse/laboratory-area-electrical-classification-richard-palluzi/ for more discussion.
The second, and more difficult type, is a hood designed to withstand an explosion. This is a very special type hood that is both very rare, very expensive, and very difficult to design. You are not picking this out of a catalog or easily converting a standard hood. See When Does a Laboratory Have an Explosion Hazard?, https://www.linkedin.com/pulse/when-does-laboratory-have-explosion-hazard-richard-palluzi for more discussion.
Handling a chemical that is flammable, combustible, or reactive (covering most of what is used!) always has the risk of problems and requires solid, well thought through mitigative measures. So be careful when you casually use the word explosion proof as it means different things in different contexts.
As usual a good discussion.
Richard Palluzi
BE(ChE), ME(ChE), PE, CSP,FAIChE
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From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU> On Behalf Of Debbie Decker
Sent: Wednesday, August 3, 2022 10:55 PM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] iron pentacarbonyl
Coming from the explosives industry, "explosion proof" has a certain meaning for me.
I reviewed what you had sent, John, and it recommends explosion proof lighting and electrical. In a typical fume hood, the light fixture is sealed inside the cupboard and only accessible from the exterior of the fume hood. All electrical outlets are also outside of the fume cupboard - which is defeated when people put a power strip inside the hood. <ugh>
All that to say ... a modern, well-engineered fume hood, with all electrical power exterior to the fume cupboard should be safe for the use of carbonyls.
Thanks for the thought exercise.
I think that Debbie's question was about the meaning or definition intended by "explosion-proof hood".
Does it mean rated as class 1 division 1 as she suggests?
Or is it a less formal meaning that the hood structure won't give way, or will blow out vertically, or another similar meaning that isn't class 1, div 1.
Of course, I could be wrong. As I like to remind myself and others, "I've been wrong before, I'll be wrong again. I just happen to think I'm right this time." ;-)
Jonathan Klane, M.S.Ed., CIH, CSP, CHMM, CIT
Senior Safety Editor, Lab Manager Magazine
PhD candidate, Human + Social Dimensions of Science + Technology
College of Global Futures
School for the Future of Innovation in Society
My comment was based from the reactivity of iron pentacarbonyl as a flammable liquid, etc.
Please look at the warnings, especially "Prevention" in the attached link.
When I was in graduate research, I always took a very cautious and measured approach when I was working with or around others who were working with boranes, carbonyls and other pyrophorics, explosive & shock sensitive, etc. chemicals. That why I stated the use of an explosion-proof laboratory hood.
John Callen writes "...the meantime, Iron pentacarbonyl, as you know, is nasty stuff and should be used with extreme caution in an explosion-proof laboratory hood."
I'm wondering what you meant by the phrase "explosion-proof laboratory hood." This brings to mind for me Class 1, Division 1 electrical utilities to the hood, installed in a space with a similarly protected electrical system.
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