From: ILPI Support <info**At_Symbol_Here**>
Subject: Re: [DCHAS-L] Magnesium/Dry Ice Demonstration - fire extinguisher?
Date: Fri, 12 Aug 2016 17:53:09 -0400
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: C5A7A80F-0CC3-4A4B-A8C6-C6FD65A0F0FF**At_Symbol_Here**

I suspect that specific comment comes from my fire extinguisher page (  Sand does excludes oxygen on contact.  Bulk NaCl does the same.  But either one must be dry or you're courting trouble.  And the key to any Class D agent is thickness - we're talking 2-3 inches ideally, which is why the smallest Class D extinguishers sold have 30 lb of agent.  According to Amerex, their 30 lb NaCl extinguisher will extinguish 4 square feet of magnesium chips:

A few months back, the LAFD (once again) called us during the middle of the fire, this one a big magnesium recycling facility fire, and they were looking for some Met-L-X.  Given the sheer scale of the fire, relative expense of Met-L-X, and there apparently being only two buckets of the material available on the entire West Coast, our discussion led to other alternatives.  Specifically, getting bags of dry play sand from Lowes or Home Depot vs just letting the fire burn out (at which point it had already been a day).  As long as the sand is dry and piled deep enough, it will work to exclude oxygen and smother the fire.  Then you have to wait until the temperature subsides enough before cleaning up. I did not follow up to see which option they went with.

Met-L-X is sodium chloride based on Mike Fisher's earlier post on the list:  as well as the product description:  The current SDS does not list the main ingredient, only the free-flow agent that makes it work well in extinguishers and caking agents   The mechanism of operation of NaCl is that it will cake if not melt to form a crust that excludes oxygen and smothers the fire (gotta love that fire triangle/tetrahedron).  It also dissipates heat, probably better than sand, but I have no data for that.

Ansul's Lith-X, a graphite powder with anti-caking agents,is the agent of choice for lithium fires that does not cake, but it does smother.  And it excels in heat dissipation like no other agent out there thanks to the amazing thermal conductivity of graphite (a consequence of its atomic structure).  For quick comparison, the thermal conductivity of graphite is 10 to 500 W/mK vs 0.14-0.25 for dry sand and 6.5 for sodium chloride.   At the high end, that's as conductive as copper or even silver metal!  I guess that's one reason we sell quite a bit of this stuff to lithium-handling companies and university robotics/electric car teams.

Final note:  No extinguishing agent will stop burning Mg within the CO2 block of Debbie's demo - even if you smothered the whole thing under a ton of sand, it would continue to burn until either the Mg or the CO2 was consumed.  All discussion here is for Mg metal burning under "normal" conditions.

Rob Toreki

PS: I must admit I had never considered repackaging Met-L-X into small containers and charging customers 4x as much for it versus the cost of a standard 45 lb pail from Ansul. That's brilliant, although, on the other hand, I wonder how long it takes to receive another 500 gram container when you realize your first bottle wasn't enough to extinguish the fire...

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On Aug 12, 2016, at 4:01 PM, "Kennedy, Sheila" <s1kennedy**At_Symbol_Here**UCSD.EDU> wrote:

Flinn's website (below) says "Dry sand also works well." I always suspected that pouring sand on a Mg fire would leave us with a Mg fire burning until it ran out of fuel/oxidizer and a pile of really hot sand.  
Does it work?

Sheila M. Kennedy, C.H.O.
Safety Coordinator | Teaching Laboratories
Chemistry & Biochemistry |University of California, San Diego
9500 Gilman Dr. | La Jolla, CA  92093-0303
(858) 534 - 0221 | MC 0303 | YORK HALL 3150

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**] On Behalf Of Donald Abramowitz
Sent: Friday, August 12, 2016 10:30 AM
Subject: Re: [DCHAS-L] Magnesium/Dry Ice Demonstration - fire extinguisher?
I concur with having the ABC dry chem extinguisher handy for anything else that ignites.  If you want to have Class D capacity on hand sufficient to handle a coil of magnesium ribbon, Flinn Scientific will sell you a 500 g jar of a Class D fire extinguishing powder for a mere $16.95.  (Catalog No. SE3004) that would be perfect to pour onto the burning ribbon.
Don Abramowitz
Bryn Mawr College
Bryn Mawr, PA

From: DCHAS-L Discussion List <dchas-l**At_Symbol_Here**> on behalf of Debbie M. Decker <dmdecker**At_Symbol_Here**UCDAVIS.EDU>
Sent: Friday, August 12, 2016 12:30:04 PM
Subject: [DCHAS-L] Magnesium/Dry Ice Demonstration - fire extinguisher?
We currently do a magnesium/dry ice demonstration in which about a meter of magnesium ribbon, closely coiled, is put into a well drilled into a block of dry ice.  The ribbon is ignited using an electric lighter and another block of dry ice is slid over the magnesium.  Cue spectacular bright flamage, sparks, and a glowing chunk of dry ice..  One of my personal faves.
We've defaulted to having a Class D fire extinguisher on site for this particular demo.  All of the other demos that produce flame can be managed with an ABC dry chem extinguisher.
But the Class D extinguisher is heavy (>75 pounds) and difficult to use.  The fire extinguisher maintenance folks don't want to maintain it, our on-site fire department would rather we not have it and would probably just let the metal fire burn itself out.  I've also done a bit of digging and ABC dry chem will work on a magnesium fire, perhaps not as effectively as the Class D but it'll work.
I'm inclined to stop hauling this thing around - it's a back injury/workers comp claim waiting to happen - in favor of having just our ABC dry chem extinguisher on site.
What do you all think?
Debbie M. Decker, CCHO, ACS Fellow
Safety Manager
Department of Chemistry
University of California, Davis
3467 Chemistry Annex
1 Shields Ave.
Davis, CA  95616
(530)754-7964 (T)/(530)304-6728 (cell)
Birkett's hypothesis: "Any chemical reaction
that proceeds smoothly under normal conditions,
can proceed violently in the presence of an idiot."

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