In attempting to develop a closed pressure vessel test for assessing explosivity, arising from propagation of detonation, deflagration or thermal explosion, some difficulties were encountered in relation to United Nations test methods. This led to a review of these methods and comparisons of their performance according to available data. The review supports the contention of several authors that the UN methods are not optimal. Agreement between methods for a given property tends to be poor and some tests appear inherently unreliable. This is especially the case with the various vented pressure vessel tests, which are capable of both under- and over-estimating explosive potential depending on the particular circumstances. The need for improving the situation is clear and is highlighted by the current move to a globally harmonised system for classifying dangerous materials. It is intended that such a system will cover storage and supply as well as transport. In the additional circumstances, reliable assessment of explosivity is arguably even more important than in the transport situation. One step forward could be to introduce a closed vessel test. In the short term, however, such a test could only be introduced as a limited screen due to the vagaries of the current tests.