The United Nations recommendations on the Transport of Dangerous Goods give guidelines for the procedures to be followed in order to determine whether materials should be classified as explosives and, if they should, to which hazard division they should be assigned. This report details studies of two materials, a demolition explosive and an energetic plasticiser, designed to determine their hazard classifications. Comments are made on the UN scheme and on its interpretation. Conclusions include K10 liquid should be removed from the UN explosives class since test results demonstrate such a classification to be unrealistically severe. Under the present UN scheme, PE4 is correctly assigned to HD1.1D. However, PE4 is a low sensitiveness, low explosiveness material and this assignment is believed to be unnecessarily severe. and 3 The choice of ignition or initiation stimulus in the package and stack states of UN Series 6 should be based on a test of the product employing a severe mechanical shock such as bullet impact rather than on the proposed end use of the product.