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An examination has been made of the critical voltages on the body for the ignition of the most easily ignitable mixtures of methane and air and of hydrogen and air by electrostatic spark discharges from the body to earthed electrodes of optimum dimensions.
At normal temperatures, the critical body voltages for the ignition of methane and hydrogen are 5.5 and 1.3 kV, respectively. The effects on the critical body voltage of increasing the temperature of the gas and the electrode independently to up to 80°C indicate that the primary factor controlling the ignition of methane is the temperature of the electrode, which in the present work is the cathode. An increase in the temperature of the electrode generally causes a fall in the critical body voltage. With the electrode at 80°C, the lowest voltage on the body for an ignition is 4.8 kV.
An increase in the gas and electrode temperatures has little effect on the critical body voltage at which hydrogen is ignited, the lowest value remaining at 1.3 kV.
The author suggests that the importance of the electrode rather than the gas temperature on the critical body voltage, particularly with methane, arises from the effects of electron emission at the electrode on the incendiary behavior of the gas, but this needs to be confirmed.
electrostatic sparks, critical body voltage, ignition hazard, methane, hydrogen, minimum ignition energy, temperature effect, electron emission, corona discharge, protective clothing
Principal research officer, Apparel and Domestic Textiles, Shirley Institute, Manchester,