Re: Definition Help

[Chuck Cooper <ccc@pp.pdx.edu>]

 Metals generally considered to be pyrophoric in certain conditions are:

aluminum, calcium, cerium, cesium, chromium, cobalt, hafnium, iridium, iron,

lead, lithium, magnesium, nickel, palladium, platinum, plutonium, potassium,

rubidium, sodium, tantalum, thorium, titanium, uranium, and zirconium.



Pyrophoric Definition: According to Webster's dictionary, "pyrophoric" (1)

means "igniting spontaneously, as certain finely divided materials". The word

"pyrophoric" has also been defined (2) as "producing sparks, when rubbed, or

burning spontaneously in air, e.g. finely divided metals". Thus, a pyrophoric

material is any material that ignites spontaneously or emits sparks when

rubbed, scratched, or struck. Chambers' technical dictionary (3) defines

pyrophoric powders as "finely divided powders which take fire or oxidize

extremely rapidly when exposed to the air; usually a metal or a mixture of a

metal and its oxide". By another definition, (4) a pyrophoric material is "any

liquid or solid that will ignite in air below 130°F (54.4°C)." In consideration

of the many fire and explosion incidents that have occurred involving the

handling, transportation, and shipment of many materials in such diversified

physical forms as metal machine turnings, chips, pellets, derbies, massive

metal, etc., any definition of pyrophoric material should not be restricted to

finely divided powders. "Pyrophoricity" (spontaneous ignition or rapid

oxidation) as used in its broadest sense, therefore, must also include massive

pieces of material, pure metals, alloys, carbides, hydrides, non-metallic

materials, and even liquids such as the aluminum alkyls. Source: Charles R.

Schmitt, P.E., C.H.C.M.



According to the chart here: http://www.reade.com/Safety/dust.html , uranium

dust is "pyrophoric" at 20 C. In my experience, dust explosions generally

require that they be well mixed with air so that they form a dense cloud and

they require an ignition source such as a spark.





Muckerheide wrote:



> pyrophoric?

>

> From: "L. A. Doerr" <lawrence_doerr@bigfoot.com>

>

> > I'm ashamed to admit it, but I just forgot the term for spontaneous

> > combustion of a substance when it is exposed to air.  I'm thinking of silo

> > dust, metallic oxides <w>, etc..  Can someone send that word along please.

> > Thanks.

>

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