PREPARING AN F.O. STORAGE TANK FOR INTERNAL EXAMINATION (SURVEY)

Keeping safety of personnel paramount, the tank is gas-freed and made safe before entry under the requirements of the code of safe working practices and MARPOL (for oil residue) and the company's enclosed-space entry procedure.

Procedure

1. Pre-job planning and risk assessment: Identify the tank, inform the watch/ duty engineer, prepare a written risk assessment and a permit-to-work / enclosed space entry permit; brief all personnel, appoint a responsible officer in charge and a competent entry team/ stand-by watch.
2. Check tank contents and position: Confirm which F.O. storage tank, its capacity, contents (heavy fuel oil/ intermediate), and plan the transfer.
3. Empty the tank: Transfer the fuel out to another storage tank or settling tank using the transfer pumps, working through the sounding/ vent. Take care not to overfill the receiving tank; monitor soundings. Do not discharge any oil overboard (MARPOL reg 12); arrange for any sludge/ residue to be kept in a slop/ oily water system or to a reception facility.
4. Isolate the tank: Close and secure the suction valve (from the tank to the service system) and any filling/overflow/ vent valves connecting to the bunker system; lock off or blank them, and tag the valves with "isolated for tank entry".
5. Clean the tank: Drain as much as possible. Then, using appropriate means, remove sludge and residue; where possible, wash with hot fresh water (or use an approved tank-washing/ cleaning arrangement to a slop tank), and heat the tank (by steam coils/ heating) to lower viscosity and aid stripping. Remove deposits and scale. Where required, use the tank stripping/ evacuation means to a slop tank; never discharge residue overboard.
6. Gas-free (ventilate) and test the atmosphere: Connect the tank ventilation/ opening; ventilate thoroughly (mechanical ventilation/ natural) until the monitored atmosphere is safe. Before entry, test the tank atmosphere using an approved gas detector for: oxygen (O2 20.9% normal, min 19.5%); flammability (lower explosive limit - below 1% of LFL, i.e. essentially no flammable vapour); and toxic gases (hydrogen sulphide, carbon monoxide, hydrocarbon vapour). Re-test at set intervals.
7. Enclosed-space entry permit: Complete and sign the enclosed space entry permit; maintain a competent watch outside at all times, with a means of communication; provide for rescue/ emergency arrangements and a first-aid/ rescue plan; use a lifeline/ harness and a personal monitor where required.
8. Perform the internal examination: The surveyor/ attending engineer enters to carry out the internal examination - visual inspection of internals (stiffeners, tank top/ bottom, bulkheads, suction, coils, condition of coatings), thickness measurement (UTM) where required, and check for corrosion, pitting, cracks, and condition of the tank. Take representative test readings/ samples as required. Only personnel certified/ trained for enclosed space entry enter; obey time limits and continuous monitoring.
9. Withdraw and re-commission: When complete, all personnel exit, the manhole is closed and re-secured, the tank is re-vented/ purged as required for fuel service, and the suction/ vents are un-isolated and the tank re-pressurised/ refilled; carry out a leak/ stand test where needed.
10. Record: Complete the entry log, permit closure, and the survey record; retain findings for the classification report.