DCHAS-L Archives, Jan 29 2014 - Re: [DCHAS-L] Met-L-X or Lith-X Extinguishing Medium

Graphite works by excluding air and conducting heat away from the burning material. This latter property is what makes Lith-X and copper powder such effective extinguishing agents compared to ordinary dry powders or sand which will trap heat. For example, consider these thermal conductivities in W/(mK):

Which is really amazing when you consider the highest thermal conductivity is diamond at about 1,000 W/(mK). These numbers pretty much rule out the poor man's Class D agent, sand, in my mind. I've heard that graphite also intercalates the lithium, but I have no references that confirm that mechanism. BTW, NaCl is interesting because it will melt and form a crust over the burning metal.

I found another important reference in regard to the original question. Ansul has a white paper on dry chemical agents which states that a Class D fire requires about an inch of material over the entire surface of the fuel in the vicinity of the fire. That translates to about 10 lbs of agent per square foot! See https://www.ansul.com/en/us/DocMedia/F-98172.pdf Which explains why the Class D extinguishers are all 30 lb.

Rob Toreki

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On Jan 29, 2014, at 8:29 PM, Ernie Lippert <ernielippert**At_Symbol_Here**TOAST.NET> wrote:

Many years ago I worked at a facility where a process using several kg of molten Li was being developed. A lot of graphite dispersed in a light oil was used as an extinguishing agent, although I never observed it in use. I was told at the time that the reaction Li(liquid)+C is endothermic.
Regards,
Ernest Lippert

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Brandon S. Chance
Sent: Wednesday, January 29, 2014 5:22 PM
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Subject: [DCHAS-L] Met-L-X or Lith-X Extinguishing Medium

DCHAS,

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.

Regards,

Brandon S. Chance, M.S., CCHO
Program Manager, Chemical Safety
Environmental Health and Safety
Princeton University
262 Alexander Street
Princeton, NJ 08540
609-258-7882 (office)
609-955-1289 (mobile)
609-258-1804 (fax)

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