From: David Roberts <droberts**At_Symbol_Here**DEPAUW.EDU>
Subject: Re: [DCHAS-L] Magnesium/Dry Ice Demonstration - fire extinguisher?
Date: Fri, 12 Aug 2016 12:40:32 -0400
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: 0C853F99-53F1-4278-9A58-8D171FAF7BC3**At_Symbol_Here**

My 0.02 on this.  I know you know this, but this is part of my thinking here.  As a firefighter, they teach us a few things about this whole concept.  You can put out fires a few ways.  Perhaps the easiest is to remove the fuel (or wait for the fuel to burn out).  In this case, any fire that gets started won't be your magnesium (it's already on fire - and in fact the CO2 is enhancing burning so it's going away quicker).  The fire you are going to have to put out will be caused by the magnesium burning (so a wood board that is sitting nearby, a vat of whatever, something that is not magnesium or CO2 (obviously).  With that said, the fire protection I think you need is for other items that catch on fire due to the demo.  The magnesium will burn out fairly quickly (there isn't enough there to really worry about).

What that means is that any type of extinguisher (including CO2 but might be better to use something else) should work here.  Now - don't leave a big pile of magnesium (where you get the ribbon from for example) sitting next to this in a way that it could catch on fire ;).  So I wouldn't worry about the Class D extinguisher.  I'd have a good ABC one ready to put out other things that catch due to falling/flaring/??? magnesium shards.

Hope that helps and makes sense


On Aug 12, 2016, at 12:30 PM, Debbie M. Decker <dmdecker**At_Symbol_Here**UCDAVIS.EDU> wrote:

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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