Brandon,

 

I asked one of our consultants to address your issue who recently helped another university lab.  His response:

 

 

There are a number of issues involved in fire control/extinguishing and certainly the agents/methods-used are a key concern.

 

In my background, I have been involved with training, and on occasion, having to put out laboratory-scale fires involving "energetic" or pyrophoric or metallic materials. Most of my actual lab experiences were with alkyl aluminum compounds. I have not had any experience with large scale industrial fires with these materials.

 

I have had significant experience with large scale industrial fires but those were mostly flammable organic materials, mostly "solvents" and hydrogen - lots of hydrogen fires. In laboratories where such materials were present, we always had solid commercial extinguishers present.

 

There are several class D fire extinguisher agents available; some will handle multiple types of metals, others will not.

 

•           Sodium chloride (Super-D, Met-L-X or METAL.FIRE.XTNGSHR) contains sodium chloride salt, which melts to form an oxygen-excluding crust over the metal. Useful on most alkali metals including sodium and potassium, and other metals including magnesium, titanium, aluminum, and zirconium.

•           Copper based (Copper Powder Navy 125S) developed by the U.S. Navy in the 70s for hard-to-control lithium and lithium-alloy fires. Powder smothers and acts as a heat sink to dissipate heat, but also forms a copper-lithium alloy on the surface which is non-combustible and cuts off the oxygen supply. Will cling to a vertical surface. Lithium only.

•           Graphite-based (G-Plus, G-1, Lith-X, Pyromet or METAL.FIRE.XTNGSHR) contains dry graphite that smothers burning metals. First type developed, designed for magnesium, works on other metals as well. Unlike sodium chloride powder extinguishers, the graphite powder fire extinguishers can be used on very hot burning metal fires such as lithium, but unlike copper powder extinguishers will not stick to and extinguish flowing or vertical lithium fires. Like copper extinguishers, the graphite powder acts as a heat sink as well as smothering the metal fire.

•           Sodium carbonate-based (Na-X) used where stainless steel piping and equipment could be damaged by sodium chloride based agents to control sodium, potassium, and sodium-potassium alloy fires. Limited use on other metals. Smothers and forms a crust.

•           Some water based suppressants may be used on certain class D fires, such as burning titanium and magnesium. Examples include the Fire Blockade and FireAde brands of suppressant.[18] Some metals, such as elemental Lithium, will react explosively with water, therefore water-based chemicals should never be used on such fires due to the possibility of a violent reaction.

 

Most class D extinguishers will have a special low velocity nozzle or discharge wand to gently apply the agent in large volumes to avoid disrupting any finely divided burning materials. Agents are also available in bulk and can be applied with a scoop or shovel.  There are a number of "complications" with Class D fires:

• the extinguishers used for best effect depends strongly on what is burning. 
  • It is wise to actively manage the inventory of type D combustibles, including minimizing inventory on hand and removing materials no longer needed. 
    • There is always stress between minimizing costs [we got it/let's keep it] vs better safety [will we really use it again? how dangerous is it? handle it like peroxide formers with a date for removal?] and safety should win.
    • Regulate other nearby flammable inventory [Why did I do that next to the ethyl ether cabinet??]
    • Use all logical engineering controls - fume hoods, glove boxes, vacuum lines, etc.
    • Demand the use of the correct personal protective equipment including face shield+goggles [yes, I know the gloves are confining...]
  • Regular review [we did it when we checked the eye-wash fountains] of the extinguishers on hand vs what they might need to fight.
  • Management [PI? Lab manager? Lab director? Etc.] must demand that everyone using such materials:
    • be trained. 
      • it is wise to train periodically and to keep records of training.
      • these fires are easy to spread and so care has to be taken not to try to "blow it out" with an extinguisher. 
    • have a healthy respect for such materials.
  • Finally, I think the argument of "having a supply of powder and a scoop nearby" vs a commercial extinguisher should be approached with care.
    • Were a legal problem to arise, it might be hard to prove sufficient preparation and concern for employees if there were not an extinguisher.
    • On the other hand, it is really handy to have an "open supply" if you have a spark that you could easily put out without tapping a full extinguisher. 
    • If I did have an "open supply", and I did back in the day, I would and did also have a commercial extinguisher just in case the spark got out of hand.  
• the "sodium chloride" type - Met-L-X, for example is probably the most widely used and available but it is not ideal for all fires, such as lithium metal. Copper powder is best there because of the alloy formation.

 

Hope this is helpful.