Subsequent to an explosion during the manufacture of an azodicarbonamide formulation, it was shown that bottom-initiated decompositions in azodicarbonamide powder could achieve much higher deflagration rates under a given degree of confinement than downward or horizontal decompositions. The need arose, therefore, to establish vessel relief requirements for bottom-initiated decompositions in a range of azodicarbonamide-based products. This was fulfilled by venting trials on a range of scales from 1 kg to 1.5 tonne. The venting requirements determined in these trials correlated poorly with the results of internationally-recognized standard laboratory tests. A better correlation was observed with maximum rates of pressure rise from a closed vessel test. This correlation could be improved by taking into account other physico-chemical properties of the powders.