This paper considers the risk of ignition of a flammable atmosphere
within a chemical cargo tank by an electrical discharge from a water
slug originating from a washing machine. Simple safety criteria are
identified on the basis of new and existing measurements of space
potential, assessed via an existing computational model which has
been revised to account for other generally present charged objects.
These criteria specify limitations for tank size, nozzle throughput
and nozzle number for application regardless of residue type. The
limitations roughly coincide with the largest tank sizes and water
throughputs characteristic of chemical tankers and their washing
operations. They are consistent with the good safety record of such
operations as currently performed. However, the findings indicate
that the situation has been reached where the proponents of changes
in current practice need to demonstrate clearly the inherent safety
of such changes.