Circular issued by International Group clubs There have been several large fires in cargo ships over the past two years, which have been attributed to the carriage of calcium hypochlorite. In response to these casualties the International Group of P&I clubs established a calcium hypochlorite working group which has met to share information and listen to the views of scientific experts. The results from full-scale tests on package sizes routinely used when shipping calcium hypochlorite in freight containers indicates that the transport requirements in the IMDG Code are inadequate. Calcium hypochlorite is classed as an oxidising substance (IMDG Class 5.1). It is manufactured in various forms, both high strength ("HCH") and low strength known as bleaching powder. Hence the various UN classifications. All forms of calcium hypochlorite will react violently when contaminated by an organic material. The reaction will generate heat and oxygen, which will feed any resulting fire. Impurities can be introduced either via insufficient or damaged packing material alternatively due to poor manufacturing standards. The product is also self-reactive and sensitive to high temperatures: sensitivity increases as the package size increases. Recent research on hydrated HCH (UN 2880) indicates that a violent reaction can occur at temperatures that are encountered by vessels transiting tropical areas. The Critical Ambient Temperature (the temperature at which a violent decomposition of the material occurs) for a 20ft freight container packed with 432 drums of 40 kg (net) of UN 2880 is calculated by the scientists to be about 37°C. The Critical Ambient Temperature for a 20ft freight container packed with 80 drums of UN 2880 of 200 kg (net) is calculated to be about 30°C. For a violent reaction to occur, these temperatures would have to be maintained for up to 3 weeks, although at higher temperatures (or if the product is impure) this period is reduced considerably. The IMDG code today