STP986: The Flammability of Aluminum Alloys and Aluminum Bronzes as Measured by Pressurized Oxygen Index

    Benning, MA
    Consulting engineer, Allentown, PA

    Zabrenski, JS
    Principal safety engineer and senior safety engineer, Air Products and Chemicals, Inc., Allentown, PA

    Le, NB
    Principal safety engineer and senior safety engineer, Air Products and Chemicals, Inc., Allentown, PA

    Pages: 18    Published: Jan 1988


    Abstract

    Pressure and oxygen concentration limits for the upward propagation of combustion of two aluminum alloys and two aluminum bronzes have been determined in oxygen diluted by either argon or nitrogen. The gas mixtures flowed over the metal specimens at a flow rate of 0.33 standard L/s in a 41-mm inside diameter vessel and at various absolute pressures to 10.4 MPa (1515 psi). The standard specimen configuration used for all metals was a 6.4-mm (¼ in.) diameter rod 76-mm (3 in.) long. Rods were ignited by passing 1500 to 2000 A at 6 V DC through a 6.4-mm diameter carbon steel promoter attached to their bottom ends. The effects of sample size and geometry were studied for aluminum Alloy 6061. The threshold pressure for the propagation of combustion in the standard aluminum Alloy 6061 specimen was significantly increased by the presence of very low concentrations of argon in the oxygen. In zero-grade oxygen (0.007% Ar, 99.993% O2), 6.4-mm diameter rods burned at an absolute pressure of 210 kPa (30 psi). Adding only 0.2% argon, however, increased the threshold pressure to 830 kPa (120 psi). In contrast, the effect of nitrogen as a diluent was much less marked, probably because of the reaction of nitrogen with aluminum and oxygen to form aluminum oxynitrides. The flammability of aluminum Alloy 5356 (5% magnesium) was slightly lower than that of aluminum Alloy 6061 (1% magnesium). Measurements to determine the effects of size and geometry on the flammability of aluminum Alloy 6061, showed that increasing rod diameter from 3 to 10 mm resulted in decreased flammability. The flammability of aluminum Alloy 6061 strips, 13-mm wide, was slightly lower than that of corresponding rods of a diameter equal to the strip thickness. The flammability of 6.4-mm inside diameter tubes of aluminum Alloy 6061 with 1.7-mm wall thickness was slightly lower than that of the standard specimen. With a wall thickness of 0.8 mm, however, the flammability was slightly higher. Two aluminum bronzes (6.5% aluminum, 2.5% iron, and 90.5% copper, and 10.5% aluminum, 3.5% iron, and 85.5% copper) had flammabilities only slightly lower than aluminum Alloy 6061, despite their high copper content.

    Keywords:

    oxygen index, flammability (metals), combustion, ignition, fires, hazards, safety, aluminum, aluminum alloys, aluminum bronze


    Paper ID: STP26739S

    Committee/Subcommittee: G04.01

    DOI: 10.1520/STP26739S


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