The back-loading and carriage of hazardous oil contaminated bulk cargo on offshore supply vessels
Health and Safety Executive - Safety alert
31 March 2010
This Notice is concerned with the back-loading and carriage of hazardous 'oil contaminated cargo', otherwise known as 'slops' or 'wet bulk waste', on offshore supply vessels (OSV). Industry guidelines are available but a number of serious incidents have recently been reported where the mud tanks of OSVs have been found to contain high concentrations of hydrogen sulphide (H2S) and/or an explosive atmosphere above the cargo. The aim of this Notice is to raise awareness of good practice and thereby prevent future incidents.
This Notice is concerned with the back-loading and carriage of hazardous 'oil contaminated cargo', otherwise known as 'slops' or 'wet bulk waste', on offshore supply vessels (OSV). Although industry guidelines1 for the carriage of oil contaminated cargo by supply vessels have been published for a number of years, incidents with the potential to cause fatalities are still occurring. A number of serious incidents have been reported recently and there is concern that unless installation duty holders and vessel owners co-operate to address the issue incidents will continue.
Operations giving rise to 'oil contaminated fluids' include well clean-up, cementing, mud pit cleaning and operations where well bore fluids become contaminated with oil based mud, crude oil or condensate. In addition, fluids from rig floor drains and other tank cleaning operations could also be included.
It is industry practice to transport severely contaminated fluids via 'tote tanks' on deck. However, in the case of 'lightly' contaminated fluids, it has become common practice to use the OSV's internal mud tanks. 'Oil contaminated cargo' is typically mostly seawater contaminated with oil and mud. It is difficult to provide an accurate Material Safety Data Sheet (MSDS) for this material and it is often perceived as being non hazardous waste. However, on a number of occasions the mud tanks of OSVs have been found to contain high concentrations of hydrogen sulphide (H2S) and/or an explosive atmosphere above the cargo. It should be noted that normal bulk mud tanks on OSVs are not designed or classified to carry wet bulk cargo with a flash point of less than 60°C.
Duty holders should make available the relevant MSDS documentation of the components and mixtures to the OSV Master. The fluid should be correctly designated in accordance with International Maritime Organisation (IMO) International Maritime Dangerous Goods (IMDG) Code and International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL) requirements. A Waste Consignment Note should be completed which should reference the 'Good Practice for the Carriage of Oil Contaminated Cargoes for Transportation by OSV' Appendix II Analysis Form1.
Duty holders should ensure that prior to back-loading contaminated waste fluids, such fluids are analysed to confirm their makeup and any potential hazards. The following tests should be undertaken close to the time of loading and accurately conducted: pH, chlorides, retort (%), flash point, gas LEL, H2S, oxygen, bulk density. The tests should be conducted by trained personnel. Guidance is available from the Marine Safety Forum1
If detected or anticipated, the duty holder should ensure that appropriate measures are taken to neutralise and remove the potential development of H2S from the oil contaminated cargo before back loading onto OSV tanks.
Oil contaminated cargo should not be mixed with other oil or water slops.
Where the offshore operation producing oil contaminated fluid involves a well with open perforations, the risk assessment should consider tote tanks as the preferred method to move fluid onshore or, via the utilisation of a specialised OSV with nitrogen blanket capability for bulk tanks. Under no circumstances should such contaminated fluids be back loaded to an OSV's mud tanks.
Relevant legal documents:
Health and safety legislation
- All ships carrying noxious liquid substances in bulk, unless expressly provided otherwise, shall comply with the requirements of the Merchant Shipping (Dangerous or Noxious Liquid Substances in Bulk) Regulations 1996, as amended and Annex II of MARPOL 73/78, as amended.
- IMO Resolution A.673(16) - 'Guidelines for the Transport and Handling of Limited Amounts of Hazardous and Noxious Liquid Substances in Bulk on Offshore Support Vessels' should be complied with. Merchant Shipping Notice 1458 applies and provides details of Resolution A.673(16).
The Regulations define the responsibilities of persons including 'shippers' to package, mark and declare dangerous goods in accordance with the IMDG Code. A 'shipper' is defined as 'a person who, whether as principal or agent for another, consigns for carriage by sea dangerous goods or marine pollutants'.
- Good Practice for the Carriage of Oil Contaminated Cargoes for Transportation by Offshore Supply Vessel Marine Safety Forum 2004. Back to reference of footnote 1
- Marine Guidance Note (MGN 283 (M)) Dangerous Goods - Guidance on the Back Loading of Contaminated Bulk Liquids from Offshore Installations to Offshore Supply/Support Vessels.
- Marine Guidance Note (MGN.37 (M)) The Merchant Shipping (Dangerous Goods and Marine Pollutants) Regulations 1997.
- Marine Shipping Notice (MSN 1458) Offshore Support Vessels
Any queries relating to this notice should be addressed to:
OSD 3.3 or 5.4
Health and Safety Executive
Hazardous Installations Directorate
5.N2 Redgrave Court
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