Changes to the IGC Code have made compliance less precise than conforming to the original code because the criteria for determining the lowest cargo density anticipated becomes the highest operational cargo temperature encountered. Predicting this temperature requires judgement on the part of the shipowner and the ability to convince Administrations that the selection is reasonable.

At its 14th session in December 1984, the IMO Bulk Chemicals Sub-Committee expressed its willingness to consider amending the codes governing cargo tank loading limits.

SIGTTO and IACS believed that for Type C tanks the codes reduced protective measures available under fire conditions or increased the risk of unwanted venting of cargo. By updating the codes, protection could be improved.

The IMO’s Marine Safety Committee, at its 61st session (MSC61), agreed to change the IGC Code and made that protection available.

These new amendments mean that Type C tanks, under fire conditions, can become filled with liquid. In this situation, the Code requires that the tank’s internal pressure does not exceed 20% above the Maximum Allowable Relief Valve Setting (MARVS). IACS/SIGTTO were able to demonstrate that Pressure Relief Valves (PRVs) could prevent the tank pressure exceeding 1.2 x MARVS.

To be certain that PRVs will perform as designed, inlet pressure losses and built-up back pressures must be within the PRV manufacturer’s limits.

IMO delegated the production of these guidelines to IACS/ SIGTTO who submitted the document to the 65th session of the Marine Safety Committee (MSC65). MSC65 recommended that the guidelines should be accepted, and they came into force on 1st July 1998.

The object of this booklet is to remind shipowners and terminal operators of the improvements in safety that these amendments provide.