STP1267

    The Effects of Configuration, Forced Convection, and Oxygen Concentration on the Flammability Behavior of Electronic Equipment

    Published: Jan 1995


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    Abstract

    The flammability hazard of vented containers commonly used to enclose electronic equipment is dependent upon materials selection, oxygen concentration, container free volume, flow velocity of oxidizing gas, and flow path through the container. The current NASA approach to assessing the flammability hazard associated with these vented containers is based on the guidelines document, Flammability Configuration Analysis for Spacecraft Applications (NASA NSTS 22648). This document gives some guidelines on the flow velocities and free volumes necessary to propagate a fire inside a vented container. The guidelines are based on limited test data, and cannot be used for many common electronic box configurations. The objective of the current investigation is to elucidate the effects of various parameters on the fire hazards of electronic equipment. Epoxy/fiberglass circuit board materials typically used in electronics applications were studied. The samples were mounted in aluminum enclosures to simulate typical electronic equipment configurations. O2/N2 mixtures ranging between 20.9 to 40.0 volume percent oxygen were flowed through the container at various volumetric flow rates. The results showed that circuit board orientation effected the flame propagation rate and the tendency for flame spread to an adjacent board. Samples were oriented parallel and perpendicular to the flow direction. When the boards were orientated parallel the oxidizing gas flow, the flame propagation rate was faster. However, the tendency for flame spread was attenuated compared to circuit board samples orientated perpendicular to gas flow. The dependence of maximal board spacing for secondary ignition versus flow velocity appears to peak between 1.8 to 3.0 m/s, depending on board configuration. These results agree with some of the NASA NSTS 22648 guidelines.

    Keywords:

    electronics boxes, flammability, epoxy/fiberglass, and configurational testing


    Author Information:

    Rimanosky, EM
    Scientist, AlliedSignal Technical Services Corp. Team, White Sands Test Facility, Las Cruces, NM

    Janoff, DD
    Principle Scientist, Materials Engineering Section, Lockheed Engineering & Sciences Company, Houston, TX

    Altemir, D
    Materials Engineer, Materials and Failure Analysis Branch, NASA Johnson Space Center, Houston, TX

    Pedley, MD
    Branch Chief, Materials and Failure Analysis Branch, NASA Johnson Space Center, Houston, TX


    Paper ID: STP16435S

    Committee/Subcommittee: G04.02

    DOI: 10.1520/STP16435S


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