Recently, several videos were released, showing how pouring, mixing or pipeline transfer of liquids can lead to its electric charging, and consequently electrostatic discharge and ignition of an explosive atmosphere. In Poland, one of the most tragic events caused by electrostatic discharge took place at the end of 2014, when a significant part of the plant producing packaging for the food industry and household chemicals burned down.
What is shown in the video
The first video shows how a simple filling of a plastic (non-conductive) canister causes electric charging of the fuel inside it, which can lead to a spark flashover and ignition of the explosive atmosphere. Further two videos show the real events that occurred during the transfer of flammable liquids.
Explanation of the phenomenon of ignition of explosive atmosphere from electrostatic discharge
Mixing or transferring liquids can electrically charge them. If we use tanks, canisters, hoses or pipelines made of insulating materials in these processes, the liquid will accumulate static electricity, thereby increasing its electrostatic potential. If there is an element with a lower electrical potential in the vicinity of the liquid, an electrostatic field is created between the liquid and this object. When its value exceeds the electric breakdown resistance of the atmosphere, an electrostatic discharge occurs. In the case of flammable liquids, the spark can ignite an explosive atmosphere.
Whether or not ignition occurs largely depends on whether the electrostatic discharge energy exceeds the minimum ignition energy of the explosive atmosphere (MIE). However, it should be stressed that MIE for liquid vapours is very low and in the vast majority of cases it does not exceed 1 mJ.
For example, the electrostatic discharge energy from a bucket, human and road tank is 9, 90 and 2250 mJ respectively (for the calculation it is assumed that the capacity of human, bucket and tank is 20, 200 and 5000 pF respectively and their electrical charge can reach 30 kV).