A series of large tank explosions in the 1960s brought to light the problems of electrostatic build-up during tank cleaning. One of the leading authorities in the area of electrostatic research, physicist Dr. John Chubb, describes in his detailed report how extensive research into the cause of these explosions has made today’s tank cleaning technology the safest ever. Read Dr. Chubb's biography.
Download or read the report:
Read Dr. John Chubb’s in-depth report (PDF-file 820 KB) detailing electrostatic ignition risks from tank washing operations. (If you can't read the file, download Adobe Reader).
Introduction to the report:
Is tank cleaning still a dangerous industry?
In the late 1960s, a number of very large crude oil carriers were severely damaged by explosions while being cleaned. The washing operation itself was cited as the cause of the ignition of inflammable vapours inside the tank. But how could washing the tanks cause such a devastating result? And how has the answer affected safety management in cleaning of carriers and aboveground storage tanks today?
Electrostatic ignition risks from water jets
Studies showed that it was the water itself that was the cause of the explosions. It was discovered that the spray mist from the water jets used in the cleaning process was electrostatically charged. On its own, this was insufficient to create any lightning-like electrostatic charges to ignite residual fumes present in an empty tank. However, studies showed ‘lumps’ or ‘slugs’ of water could become charged by the mist and create electrostatic sparks on contact with projections on the inside surface of a tank such as bulkheads or girder work.
From water mist to ignition:
Electrostatic mist created from the impact of washing jets on the tank walls
Electric fields created at the edges of all projections on the tank walls
‘Lumps’ or ‘slugs’ of wash water become charged by these electric fields
Electrostatic sparks occur when these ‘lumps’ of water contact projecting tank structure
Flammable vapours in the tank ignited if sparks have sufficient energy