Shipbuilding and Ship Repair - Process: Tank Cleaning | Occupational Safety and Health Administration

Process: Tank Cleaning

Description

This process involves the removal of hazardous residue from tanks prior to repair work.

Only the tanks on barges are normally cleaned in port facilities. Because of the danger of catastrophic explosions, tanks on ships are cleaned at sea, as required by Coast Guard regulations 46 CFR 35.1-1(c)(1) for tank vessels, 14 CFR 71.60(c)(1) for passenger vessels, and 46 CFR 91.50-1(c)(1) for cargo and miscellaneous vessels. Different types of tanks require different procedures. For example, the protocol for cleaning LNG tanks differs considerably from cleaning tanks on conventional barges.¹
Although machines are used to wash tanks, the final cleaning is usually performed manually (known as "mucking"), a procedure that requires protocols for entry into confined spaces and the use of airline respirators, protective clothing and attendants.¹
Certification of tanks by a marine chemist is required before hot work can be performed in tanks.

Equipment

Butterworth, Gamajet, or other automatic cleaning machines
Ventilators - blowers and ejectors
Airline respirators and protective clothing - for hand washing or "mucking"

Associated Hazards

Fires and explosions from explosive atmospheres in tanks - see 29 CFR 1915, Subpart B for standards pertaining to explosive and other dangerous atmospheres. Residual products in bulk cargo and fuel tanks cause most disastrous fires and explosions. Fires or explosions result from failure to clean, inert and isolate tanks and adjacent spaces before starting hot work or introducing other sources of ignition.²
Fire, asphyxiation, toxic exposures upon entry into confined spaces during ship building and repair. Also, see OSHA's Confined Spaces Safety and Health Topics Page.

References

¹ Savage, K. M. "Marine Gas Hazards Control: Cleaning and Gas-Freeing Shipboard Tanks." National Institute for Occupational Safety and Health (NIOSH) Contract Report 099-74-0002 (NTIS PB-82-225-095). Proceedings of the International Shipyard Health Conference, (1973, December 13-15).

² Netterson, R.W. "Accident prevention in shipbuilding and repairing." Safety and Health in Shipbuilding and Ship Repair. Geneva: International Labour Office, 1972.