Lessons Learnt: Contamination of gas oil cargo

Vessel Type: Tanker

Incident description

After discharging a cargo of naphtha, the vessel was then fixed to load gas oil, in preparation for which, all cargo tanks and lines were washed with fresh water and stripped dry. Upon arrival at the load port, a cargo tank inspection was carried out by surveyors appointed on behalf of the shippers, which was restricted to taking dips due to the tanks being inerted. The tank atmospheres were also tested and reported to contain less than 2% hydrocarbons (naphtha vapour) which was considered suitable for commencement of loading. The loading was suspended for taking "first foot" samples from the cargo tanks, but rather than await the results of analysis, charterers instructed the vessel to continue loading. It was not until loading was well advanced that the charterers ordered the vessel to stop loading as analysis of samples indicated that the cargo flashpoint was below the specified minimum. The relatively large quantity of cargo loaded at that point meant that mitigation measures to bring the cargo back on-spec were less effective, resulting in a high value claim.

Analysis

The shore tank and ship manifold samples were on-spec, isolating the source of the problem to the ship. Two potential causes for the cargo contamination were identified: Firstly, the tank cleaning had been carried out using fresh water de-bottomed from a retention tank containing an oily mixture from the previous cargo. Secondly, it was considered likely that the hydrocarbon content of the inerted tanks was understated due to cargo vapour separating out into a naphtha rich bottom layer which may not have been detected during gas sampling. The shipowner argued that had the shippers followed the more customary practice of stopping loading until such time as the results of the "first foot" analysis were known, mitigation measures could have been taken to bring the cargo back within specification for flashpoint and otherwise reduce the depreciation in value. Although technically valid, legal advice was that the shipowner's over-riding obligation under the Hague Visby Rules was to present cargo tanks in a fit condition to receive the intended cargo.

Lessons Learnt

• The ultimate responsibility for ensuring that cargo tanks are clean and suitable for the intended cargo rests with the shipowner
• "Passing" a pre-loading tank inspection does not necessarily represent proof that the cargo tanks are in a fit condition
• If in doubt as to charterers orders for cleaning or loading operations, the master should immediately query such orders and inform the ship manager
• The early intervention of qualified surveyors and/or cargo experts may assist in resolving problems or significantly mitigate their consequences