The Loss Prevention team at UK P&I Club, in conjunction with CINS, advises on the safe carriage of calcium hypochlorite:

“Calcium hypochlorite is used as the active ingredient in a variety of water purification and bleaching agents and by nature is continually decomposing, making the substance unstable and dangerous when not handled correctly.

“At normally encountered temperatures calcium hypochlorite decomposes very slowly, releasing heat as it does so. However, at higher temperatures the rate of decomposition increases and if the heat is not able to escape from within the material then its temperature increases.

“The packaging and quantity of the substance can have an impact on self-accelerating its decomposition. A self-accelerating reaction can occur and result in serious fires and explosions. When involved in a fire, the heat and oxygen released by the decomposing calcium hypochlorite will intensify the fire. 

“Decomposition can also be accelerated by contamination with organic materials (such as oil), inorganic materials (such as metals) or moisture. If calcium hypochlorite is mixed with organic materials it can result in a fire without the need for an external ignition source.

The temperature at which the self-accelerating reaction occurs depends on the type, size and shape of the packaging. The temperature required will be higher for a small package compared to a larger package of the same material. This is because the smaller package will be able to lose heat to the surroundings much more readily than a larger package. The selection of type, size and shape of packaging to promote heat dissipation is therefore important.

Dry or reefer containers may be used provided that a proper risk assessment is undertaken. The risk assessment should include all aspects of through transport including, but not limited to, routing, climatic temperature and journey duration.

The reefer container control temperature should be 10 °C. In the event of a mechanical failure or of an interruption of the power supply, the insulation in a reefer will initially protect the calcium hypochlorite from external heating.

“However, if there is an extended interruption to cooling, heat produced by calcium hypochlorite decomposition may accumulate faster in a reefer than in a dry container. The longer the interruption, the greater the risk that calcium hypochlorite will heat up faster in a reefer container. Prompt steps need to be taken to restore the power or fix a mechanical failure or cool/ventilate the cargo.

In practice, calcium hypochlorite tends to be shipped on a full container load basis. It is not recommended that such payloads be consolidated with other cargo because this could detrimentally affect the stability of the calcium hypochlorite due to changes in the overall thermal properties of the container contents.

“Plastic drums are to be used as the packaging for calcium hypochlorite, as adequate air circulation around the containment is required in order to prevent any heat build-up. Drums offer the best solution as they provide the largest surface area to be exposed to the surrounding air.

“Packaging materials must be clean, free from contaminants, and in good condition. The drums should be properly secured on pallets and within the container. Any securing method, such as shrink-wrapping, should not restrict air flow around the drums to reduce retained heat within the cargo.

Calcium hypochlorite or calcium hypochlorite mixtures shall be transported in compliance with stowage requirements which state that during the course of transport, these substances shall be shaded from direct sunlight and all sources of heat and be placed in adequately ventilated areas. It is also recommended to stow containers of calcium hypochlorite where they are accessible.”