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Probability of Resistive Spark Ignition Caused by Very Low Currents.
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The Bureau of Mines has empirically determined ignition probability versus current for resistive circuits in an 8.3% Methane-air atmosphere. Simple ignition probability, defined as the number of ignitions divided by the total number of sparks, was determined, and the corresponding currents were recorded. The experiment was designed to minimize the probability of not observing an ignition that should occur during a series of tests. For resistive circuits in 8.3% Methane-air mixtures, the experimental results indicate that ignition was not achieved below 2,000 ma at 20 V DC, 350 ma at 30 v DC, 150 ma at 40 V DC, and 175 ma at 50 V DC. The simple probability of ignition corresponding to these currents is estimated to be, respectively, 1.0 X 10-6, 1.7 X 10-7, 3.0 X 10-7, and 1.0 X 10-5. The ignition mechanism seems to break down below this point, implying that a threshold current value exists below which spark ignition does not occur.
IH; Report of Investigations;
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division