DCHAS-L Archives, Aug 12 2016 - Re: [DCHAS-L] Magnesium/Dry Ice Demonstration

Given the small size of the demo and given that it's physically contained, I'd be comfortable manually scooping or pouring the Class D agent onto it. I'd probably go a with Met-L-X, and you could probably store some in a big wide-mouth container for easy dumping. See http://www.safetyemporium.com/09450 (disclaimer: Safety Emporium is my company's site).

An standard ABC extinguisher is going to be fairly useless on a flammable metal fire as it discharges very thinly and very wide (and can blow your burning material to undesired places). Class D agents work primarily through smothering and the extinguishers designed for those are generally designed to deliver a soft flow so you can build up several inches of agent on top without blowing everything everywhere. See, for example, this sodium chloride extinguisher - the long handle wand is designed for non-dispersing application, but has a quick-connect if you need more range and want to lob the agent: http://www.safetyemporium.com/09590 In your particular case given the extremely small amount of material it would probably be totally consumed by the time you got an extinguisher on it anyway.

You can strap large extinguishers to dolly carts. Either pick one up at your local big box retailer and put some straps on it, or purchase one made for that specific purpose: http://www.safetyemporium.com/09800

Had a call a few years back from the LAFD asking if they could use Purple K (a Class BC dry powder) agent on a titanium fire…as I started explaining that a Class D agent would be a better choice he explained that they had a shipping container full of burning titanium shavings and he had a tender full of PK….needless to say, there was a quick call to Ansul tech support on that, who said that it would be a very Bad Idea. I suspect the burn temperature is so hot that it could disproportionate the potassium bicarbonate material to make TiO2 and carbon much as your demo does. Turns out that container was sitting on a dock, I wonder how spectacular it would have been to just push that over the edge into the bay with a front-end loader (the fire would instantly disproportionate water into H2 and O2, heh).

For those interested in the demo Debbie is talking about, I have a writeup on it here: http://www.ilpi.com/genchem/demo/co2mg/index.html

Rob Toreki

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

Hi:

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?

Best,
Debbie

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)
dmdecker**At_Symbol_Here**ucdavis.edu

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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