And one more note to add to Keith's fine post and the whole discussion is to point everyone to NFPA 848, Combustible Metals, which you can read for free here although you have to create a login and password: http://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards?mode=code&code=484 (look for the free access link below the title).  

Section 6.3.3.10 is titled "Applications of Extinguishing Agents".   Section 6.3.3.10.1 specifically mentions dry sand, other dry compatible material, or Class D powders as extinguishing agents.  So that settles the dry sand question for good.

Section 6.5.2.4 lists many points about planning for such fires, including a statement at point (5) that dry chemical extinguishers on non-alkali metal fires are ineffective at controlling the metal fire, but can be useful when other materials are on fire and the metal is not yet on fire.  Wow, this whole section has some really amazing facts about flammable metal fires; I knew a lot of this but I keep finding more neat tidbits as I read it - I encourage everyone who works in this area to give this document a good read!

At only $59.50 for a PDF of print copy, I'd say any organization working with flammable metals would want to purchase this one if they don't have it already.

Rob Toreki