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.

Fixed-machine water washing generates atomized water mists that retain an electrostatic charge. Inserting portable equipment or drop lines into an electrostatically charged atmosphere creates an ignition hazard if a spark occurs. Pursuant to ISGOTT guidelines, the tank must be thoroughly ventilated to discharge the charged mist before rigging portable washers.