AN-based fertilizers are not safe, warn decomposition accidents
As of 1630 UTC Aug 26, bulk carrier CHESHIRE and SAR tugs were some 60 nm southeast of eastern coast of Gran Canaria. Decomposition in Holds 1 and 2 is still on, emitting a lot of toxic fumes, so technicians still can’t board the hapless bulk carrier.
One site’s visitor sent to me a very interesting link to the investigation report on “a self-sustaining decomposition event of the NPK (Nitrogen, Phosphorous and Potassium) fertilizer freight aboard the ship Ostedijk”, which took place in Feb 2007 in Spanish waters. Except scale (6012 tons on OSTEDIJK against 40,000+ on CHESHIRE), CHESHIRE’s fire is a replica of OSTEDIJK fire (photo of OSTEDIJK fire below). All those concerned and interested should read this report: https://www.researchgate.net/publication/250275883_Investigation_of_the_Fertilizer_Fire_aboard_the_Ostedijk
Among investigation findings, I figured out those most important from my point of view:
- The decomposition chemistry of AN-based fertilizers is complex. Little information is available on the precise decomposition chemistry of AN-based fertilizers as the compositions can vary greatly.
- The decomposition behaviour and subsequent classification of AN containing fertilizers is determined by a standardized propagation test (the “Trough Test”) as detailed in UN Recommendations on the Transport of Dangerous Goods. This test provides only limited information i.e. whether or not the fertilizer will support SSD under the prescribed conditions and therefore it is not always applicable to other situations where the conditions are different.
- Although AN-based fertilizer is classified as a class C fertilizer i.e. one which will not sustain decomposition in the trough test UN Transport Code, the fertilizer cargo ignited and an SSD fire grew rapidly for seven days. This points at the limitations of the trough test and the lack of attention given to fertilizer fires by the research community.
- Incidents of this nature which, due to the absence of oxygen chemistry, challenge the traditional concept of fire are sometimes studied by the chemical engineers but largely ignored by fire safety engineering.
My own conclusions, with relation to this ongoing accident, are as follows:
Most probably, there won’t be a major explosion;
Most probably, vessel will survive fire without major disaster, like cracks in the hull and broking in two;
CHESHIRE fire expertise will be a substantial contribution to AN-based maritime accidents knowledge;
As of now, no methods exist, which may check and guarantee the safety of AN-based materials during seaborne transportation;
Major explosion in such accidents can not be excluded;
Coastal States just can’t be excessively cautious when encountering such accident in their waters, and if crew are evacuated, maybe the safest way is to let such ship drift further out to sea, or prevent her drifting towards the shore by towing her as far as possible, and wait until cargo decompose. Nobody knows the scale of the explosion of tens of thousands tons of ammonium nitrate, and its’ devastative effects, including generated by explosion wave.
August 27, 2017