NFPA 10, Standard For Portable Fire Extinguishers, was updated for 2013 with several changes regarding Class D agents, and my understanding is that the changes were mostly made to address containers of dry powder which had not previously been included as they are not "fire extinguishers" in the mechanical sense of the word. There was apparently some debate about including pails in the standard, but there they are.
In theory, you can view (but not print, save etc.) the NFPA standards by creating a free account with them on their web site, http://www.nfpa.org
. On my system this failed miserably because they are using Java on a non-secure http connection, and my system software won't play with something that's that big of a security threat. I was able to view them by making the request from an outdated machine.
6.5.4 of NFPA 10 regarding Class D units is that "Size determination shall be on the basis of the specific combustible metal, its physical particle size, area to be covered, and recommendations by the the fire extinguisher manufacturer based on data from control tests." Which, in the context of your question says to me that if you don't have large quantities then you don't need a large extinguisher and, if sane judgement calls for it, then a pail and scoop will work.
184.108.40.206.1 of NFPA 10 says that agents "for scoop or shovel application on metal fires shall be kept full and sealed with the lid provided with the container." So make sure that becomes part of your inspection procedures and maybe put a sign or label on the unit and wall to that effect.
Then again, I prefer the Class D extinguishers with wands as you can lob the agent at the fire from a distance. Dollies for these are also available if you find them too heavy. Also note that the NFPA standards are biased towards straight metal fires rather than solvents mixed with pyrophoric agents. Would you want to put out a solvent fire with a scoop? I know that if someone drops a 500 mL bottle of an alkyllithium in hexanes, I'd be much more comfortable with a Class D extinguisher versus a scoop and pail, which is why I ordered them for my research labs when I was a professor.
The other half of your question regards picking the proper agent. The advantages and limitations of a wide variety of commercially available Class D agents is discussed to some degree in NFPA 484, Standard for Combustible Metals, and in Section 6, Chapter 9 of the NFPA Fire Protection Handbook, but again, seem do deal with metals rather than organometallics. The NFPA Fire Protection Guide to Hazardous Materials should have similar information but I have not perused it.
In the context of what people seem to buy (as my company sells both the extinguishers and agents), a lot of laboratories do go for the Met-L-X or Lith-X pails and a scoop. Met-L-Kyl is actually the best option for organometallic fires, but it's hideously expensive. Lithium battery storage/production/research folks and the military go for Lith-X most commonly (we recently shipped 8 pails to Afghanistan, in fact), although there is occasional demand for the more expensive Navy copper agent. NaCl extinguishers are less popular despite having the lowest cost, probably because of the limitations of the agent. Disclaimer: this is my company's web site - see http://www.safetyemporium.com/ILPI_Site/WebPagesUS/safety/extinguishers.htm
to get an idea of the relative prices and for manufacturer descriptions and suggested uses of the agents.
Debbie's comment that their fire folks do not permit class D extinguishers was interesting. Without a Class D present, folks might be tempted to use a CO2, water, Halon or other dangerously inappropriate extinguisher on a Class D fire. But again, it's all in the size/risk assessment, so if that works for a given lab, that's fine - I just don't like the idea of blanket policies that prohibit them if the lab personnel want them. Finally, concern about the "wrong" Class D seems to me to be a minimal one - in general, you're talking only about a less effective extinguisher which, for most fires will still manage to snuff a lab sized fire anyway (see Met-L-X vs Met-L-Kyl above).
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I am looking into the advantages and disadvantages of using Met-L-X or Lith-X scoopable dry powder extinguishing agent versus outfitting labs with the extremely large dry powder extinguishers that this material traditionally comes in. I am hoping for
a solution for the usual pyrophoric and reactive metal suspects; alkyllithiums, trimethyl aluminum, diethyl zinc, potassium, sodium, magnesium, etc.
If anyone has an experience with using or training with this extinguishing, I would appreciate any insight that you might have. I have already contacted Ansul and am awaiting their response.
Brandon S. Chance, M.S., CCHO
Program Manager, Chemical Safety
Environmental Health and Safety
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