It’s not only bosuns who can get explosive when agitated, so can certain types of waste warns the Marine Safety Forum. Although the safety alert concerns a close-call rather than an accident it’s advice is worth taking.
Says MSF: “There was a request from the platform to backload four packets of wet bulk waste, also known as “slops”, into the OSV’s mud tanks. All associated testing of the waste and paperwork were provided and agreement was reached by the vessel and installation to proceed with the backload.
The composition of the waste was 88% seawater, 7% base oil and remainder small percentages other solid additives.
The specific gravity of the waste was documented to be around 1.09 although this cannot be confirmed and the vessel asked the platform if there was a need to agitate the waste. The platform confirmed that there was no requirement to agitate due to the composition of the waste but if the vessel felt it needed to be done then it was ok to agitate.
Prior to entering port the vessel decided to agitate all the tanks just in case there was any settlement over the previous days which may cause difficulties on discharge.
Once alongside the surveyor arrived to gas test the tanks as per procedures. Atmosphere tests on three tanks showed a LEL of 10%, and within the parameters; however one tank (No. 1 Port) showed 20% and increasing. The job was stopped and a discussion took place with interested parties on how best to deal with this issue.
The three tanks showing 10% LEL were emptied and cleaned with forced ventilation being used on the remaining tank. After a period of time a further gas test result showed the LEL level had reduced to acceptable limits and the tank was emptied and cleaned.
• The composition of the waste was possibly a catalyst for the generation of an explosive atmosphere.
• The agitation of the tanks was found to be a contributing factor for the increased LEL
Appendix A of the North West European Area Guidelines provides detailed information on the procedures / advice when dealing with Wet bulk Waste.
All parties are strongly advised to review the relevant section of the guidelines.