You have water washed your cargo tanks using the fixed machines. What should you do before using portable machines to clean areas screened from the wash of the fixed machine by structural members?

Correct Answer: Option D — Ventilate the tank to eliminate any electrostatically charged mist.

High-pressure water washing generates a charged water mist that retains an electrostatic charge for a period after washing stops. Introducing portable equipment into a charged atmosphere creates a risk of spark discharge and explosion. Per ISGOTT guidelines, tanks must be thoroughly ventilated to clear electrostatically charged mist before introducing portable equipment.