Combustible Metal Dust as Defined by the NEC

An atmosphere classified as hazardous Group E contains combustible metal dusts.

a) True
b) False

See answer and applicable Code reference

The correct answer is: a) True

For purposes of testing, approval, and area classification, the Code groups various air mixtures and presents them in Sec. 500.6 of the 2011 NEC. As noted in 500.6(B)(1), Group E is defined as "Atmospheres containing combustible metal dusts, including aluminum, magnesium, and their commercial alloys, or other combustible dusts whose particle size, abrasiveness, and conductivity present similar hazards in the use of electrical equipment."