Dealing with polymerisation hazards

CHILL OUT

POLYMERISERS • THE RISKS POSED BY DIVINYL BENZENE IN MARITIME TRANSPORT HAVE BEEN RECOGNISED; INDUSTRY GUIDANCE NOW EXPLAINS HOW TO CARRY IT SAFELY

AMENDMENT 39-18 OF the International Maritime Dangerous Goods (IMDG) Code takes mandatory effect from 1 January 2020 but can be applied on a voluntary basis this year. This latest edition includes further changes to the provisions applicable to the carriage of polymerising substances, following the introduction of a new subdivision in Class 4.1 in Amendment 38-16.

These changes were largely prompted by the explosion and fire aboard the containership MSC Flaminia in the Atlantic Ocean in July 2012. Investigation identified that the origin of the fire was in two tank containers containing divinyl benzene (DVB). The cargo had polymerised spontaneously, generating a large amount of heat that affected other containers. Three crew died in the incident and the financial losses are expected to be at least $280m.

To help improve safety during the carriage of DVB in tank containers, new guidelines have been published by the Cargo Incident Notification System (CINS), the International Group of P&I Clubs (IG) and the TT Club.

The guidelines note two changes that have been introduced into shipping practices for DVB. Firstly, while DVB has been shipped for many years with very few incidents, since 2006 it has tended to be shipped in a higher concentration – 80 per cent (as was the case in the MSC Flaminia incident) rather than 60 per cent. Moreover, it is also being regularly carried in tank containers without temperature control, rather than in drums packed in refrigerated containers.

Since these new practices were introduced, the guidelines say, there has been an increase in the frequency of polymerisation incidents; so far, these have mostly taken place before the cargo has been loaded aboard ship, and most often when the DVB is being shipped from the warmer regions of the US in the summer.

BETTER IN DRUMS DVB is shipped under UN 3532 if stabilised or UN 3534 if shipped under temperature control. When shipped without temperature control, special provision 386 of the IMDG Code now requires that a risk assessment is carried out to determine if the level of stabilisation is sufficient to prevent the substance from polymerisation. In effect, stabilisation is effective only when the DVB is loaded at a sufficiently low temperature and the total journey time to the receiver is short enough. Ambient temperatures must be taken into account.

The guidelines say that the inhibitors most commonly used to prevent polymerisation in DVB require oxygen in order to work and begin to break down and become ineffective at temperatures above 27˚C; some shippers now chill DVB before loading into a tank container and endeavour to arrange transport so that the journey time is short enough to avoid polymerisation.

However, the guidelines strongly recommend that DVB is only carried in drums in a refrigerated container, or in a refrigerated tank container.

One other vital issue that emerged from the MSC Flaminia case is the importance of all parties in the supply chain having access to information on all aspects of the cargo. This should include all assumptions made by the shipper, so that the carrier can make appropriate provisions for the transport of the cargo. HCB

The guidelines are available from the CINS website at www.cinsnet.com/industryguidelines-for-carriage-of-dvb-incontainers-published/.