Members may recall a recent Newsletter article which drew attention to the emission of toxic gas from a consignment of thiourea dioxide. Reports of similar incidents indicate that this was not just an isolated occurrence. 

Although thiourea dioxide is not listed in the International Maritime Dangerous Goods (IMDG) Code at the present time, it is clear that the chemical has hazardous properties. The IMDG Code is to be amended in due course, but in the meantime Members should note and observe the following;

Characteristics

Thiourea dioxide (or formamidine sulphinic acid) is an odourless white to pale yellow crystalline powder. It is used in the paper and textile industry as a bleaching and reducing agent. The chemical is usually shipped in sealed fibre drums, occasionally in bags, and is often containerised.

Exporting Countries

Thiourea dioxide is manufactured in the Far East and in Europe. All recent incidents have involved shipments originating from China.

Hazards

Thiourea dioxide is harmful if swallowed and is an irritant to the skin and eyes. Although stable at room temperature it may decompose violently if exposed to heat, water or incompatible substances such as oxidising agents, metallic salts or alkalis. The reaction causes the material to self-heat and generate toxic gases including sulphur oxide, thereby presenting a hazard to anyone inhaling the fumes. Holds and neighbouring cargo may be contaminated with sulphur deposits, and sulphur oxide in contact with moisture vapour can generate strong acids which may affect other goods.

In the last three years there have been at least six incidents where severe decomposition of the material has occurred during carriage by sea.

Observations

Manufacturers quote a range of temperatures beyond which the self-heating process may be triggered. One Safety Data Sheet declares that the material decomposes spontaneously at 100C but will also decompose on lengthy heating above 50C. Another manufacturer indicates that the thermal stability is 80C for two hours, while a third states “on lengthy exposure to heat, stable up to 50C”. The behaviour of the chemical beyond these limits is not described.

Other manufacturers advise that the material should be stored in cool, dry, well ventilated areas and away from heat.

Recommendations

For the time being thiourea dioxide should be treated as UN number 3088 Self Heating Solid, Organic, N.O.S., Class 4.2. It should also be noted that in the summer of 1997, thiourea dioxide will appear in the 10th Revised Edition of the UN’s Recommendations on the Transport of Dangerous Goods as UN number 3341, Class 4.2. The IMDG Code may undergo similar changes when next amended. Part of the new entry in the UN Recommendations is expected to read as follows;

“Strong reducing agent. Violent exothermic decomposition above 100C with emission of large amounts of sulphur oxides, ammonia, carbon monoxide, carbon dioxide, nitrogen oxides and hydrogen sulphide. Extended exposure to temperatures above 50C and moisture may cause visible decomposition”.

It is also anticipated that the entry will state “Packing Group: II or III according to the grouping criteria”, listing the following details;

The material will almost certainly be classified as Stowage Category D “On Deck Only” for (a) cargo ships and (b) passenger ships carrying a number of passengers limited to not more than 25, or to 1 passenger per 3 metres of overall length whichever is the greater number. Under Category D, stowage aboard passenger ships in which the limiting number of passengers is exceeded is prohibited.

Even when stowed on deck, the temperature within a container may rise to critical levels is exposed to direct sunlight in hot climates. Placing the container in a sheltered position and shielding it with others placed overhead and to each side may be a solution, provided access is still possible. It is also important to recognise that thiourea dioxide of Chinese origin appears to be less stable than that produced elsewhere.

It is essential to keep thiourea dioxide dry at all times, and the external surfaces of containers should always be examined for holes or punctures before departure. The material should be stowed well away from other commodities vulnerable to contamination, particularly foodstuffs. Care should also be taken to ensure that shipments are not likely to come into contact with oxidising agents, metallic salts and alkalis, and that containers stuffed with combustible products are not situated nearby. However it should not be assumed that these precautions alone will eliminate the possibility of decomposition if the product itself is already unstable; pre-existing factors such as insufficient drying before shipment, damp packaging, existing impurities or inadequate packing may raise the likelihood of an incident. If a violent reaction of the material occurs on passage, self contained breathing apparatus and protective clothing must be worn if an attempt is made to bring the situation under control. Any of the customary fire extinguishing mediums may be used, although water may achieve the quickest results. Punching a hole at the top of a door or wall and flooding the entire container may be effective, bearing in mind that it will be necessary to continue with this course of action until the container can be discharged. Manoeuvring the ship so that the accommodation block lies upwind of the source of the toxic fumes would also be advisable, closing ventilation intakes as necessary.

Hong Kong – Special Requirements

The decomposition of a containerised parcel of thiourea dioxide and subsequent release of dense white toxic fumes recently led to the evacuation of 400 terminal workers in Hong Kong. Eight persons were taken to hospital after inhaling the vapour, two of whom were detained overnight.

It took three hours for the Hong Kong Fire Service to quell the reaction and it was found later that many of the drums had been leaking. The container originated from Xinjiang, China and was discharged at Hong Kong for transhipment to Indonesia.

The ambient temperature was 29C with a relative humidity of 77%. In the preceding 24 hours there had been over 4 millimetres of precipitation. Isolated and violent showers had occurred that morning.

The incident has prompted the Hong Kong Marine Department to issue Competent Authority Approval Number 1/96 which requires all movements of thiourea dioxide transported within Hong Kong waters to be stowed and packed in accordance with the IMDG Code entry UN 3088 “Self Heating Solid, Organic, N.O.S.” which the Department has modified to incorporate the changes currently under consideration. With reference to intermediate bulk containers, the notice states;

“Carriage in hermetically sealed, flexible, composite, fibreboard or wooden IBCs is only permitted with competent authority approval for each shipment. A copy of this authority shall accompany the transport documents. Valid only on the waters of Hong Kong”.

It is also stated that provisions of IMDG Code amendment 28-96 shall apply from 1 January 1997. The full text of Hong Kong Competent Authority Approval Number 1/96 may be obtained from the Loss Prevention Department.

Further Information

A number of manufacturers have produced Safety Data Sheets regarding the properties and hazards associated with the handling of thiourea dioxide. Copies are available from the Loss Prevention Department on request.

Source : West of England
February 1997