Expandable Polymeric Beads are a moulding material in the form of granules or beads, approximately 3mm diameter. The beads or granules may contain between 5% and 8% of a volatile hydrocarbon, chiefly pentane. During the moulding process the beads are heated causing expansion and fusion forming the familiar polymeric packaging material. During storage or transport the material will release a portion of the pentane. The rate of this release is increased with a rise in temperature. The beads have been found to generate flammable concentrations of gas in enclosed spaces and have been involved in several major explosions - in one incident causing severe damage to a container ship.