Old Truth Stands no Longer: How dangerous is splash filling really?
It is proven that the assumption that droplets are charged by friction with air does not hold true, and that applies to a closed liquid jet as well. But this result gained by tests in the micro-liter scale does not help very much, however, the question is, are there any electrostatic ignition risks when pouring flammable liquids at liter-scale? That means: Single drops are one matter, larger volumes of liquid that splash are something else.
But as the old saying goes, “the proof of the pudding is in the eating” — in other words: A scientific examination has to be conducted. On the contrary of investigating the droplet charge, charge measurement is no longer sufficient. It is especially important to focus on the question whether the resulting amount of charge is capable of igniting flammable liquids.
Decisive for that is the amount of energy necessary for ignition, called Minimum Ignition Energy (MIE). In the “Electrostatic Hazards Guideline IEC 60079-32-1 Table C2” a larger number of flammable liquids with their MIE values are listed and, fortunately, correlated with the relevant Minimum Ignition Charge (MIQ).
The Missing Link
This makes it possible to find out which hazards arise from splash filling of flammable liquids. However, one link is still missing: How is it possible to determine without contact the amount of charge implemented in a gas discharge?
A knowledge gained a long time ago can help further: Gas discharges manifest themselves, e.g., by cracking noises in a radio receiver of older design. As far as they feature plasmas, in general necessary for ignition, they emit high frequency signals which may be received by appropriate antennas. To measure these signals antennas were tested while connected to an oscilloscope.