In a pyrotechnic storage facility, a photogenic composition decomposed during the preparations of its destruction, thereby causing a small discharge of hydrogen sulphide (H2S). The composition, manufactured in 1979 using a base of black powder, aluminium and magnesium powder, was contained in a total of thirty 300-g bags.
As part of planning for their destruction, the bags were poured into 2 cans of water placed outside and covered with a lid. A few hours later, a technician noticed a gas release on one of the cans along with a rotten egg smell. A fire nozzle was used to initiate cooling, a step that limited the release of gases. The contents of these cans were then poured from a safe distance into tanks.
A laboratory analysis of the composition revealed nothing abnormal. A reaction involving the chemical decomposition of water molecules had taken place during contact with magnesium and aluminium powders. In turn, this reaction triggered the hydrogen sulphide release due to a re-composition of hydrogen with sulphur stemming from the black powder. This incident highlighted the hazardousness of older products, whose alterations over time (stability, sensitivity, etc.) are not always well known.
Moreover, during preparation of the product disposal phase, the guideline applied targeted the destruction of black powder, even though the composition corresponded to a mixture. Under these conditions, a preliminary safety analysis would have been necessary to introduce adequate measures.