Ignition of flammable gas/air mixtures by sparks from 2 MHz and 9 MHz sources

Choosing threshold levels for electromagnetic hazards

“…The higher source voltage enabled the spark to continue burning for a longer period as the electrodes separated, thus allowing more energy to be dumped into the transient spark and also enabling the quenching effect of the electrodes to be removed. Following this, some new series of quantitative experiments with high source impedances were undertaken and it was found that the power required for ignition was much lower than with 50-W sources and was now essentially independent of frequency [5]. A set of powers for the three flammability classes was determined by experiment (Table I) and these are now universally accepted, although the physical connection between these powers and the energies required for ignition is still very complex and not fully understood, especially since the match condition between the spark and the radio frequency source is changing continuously during the spark process.…”