In an audit of the Armed Forces smoke grenade m/56, 36 grenades were discovered with leakage, or imminent risk of leakage. The grenades contain white phosphorus, which is a very reactive substance. It ignites spontaneously in air and burns through clothing and skin very quickly. Risk of serious injury exists, when handling a defective smoke grenade. FOI, commissioned by FMV, investigated 144 grenades, of which 63 were selected for further studies. The goal was to determine the causes of the leakage. Two different manufacturers have produced these grenades through the years, the leaking specimens all come from the manufacturer Nora fuse factory AB. Reference copies of the first manufacturer, Linde kvarnmekaniska, have also been investigated. The study began with a visual inspection of grenades. Then a number were depicted by X-ray, and finally some of the grenades were disassembled. Because of the risks in handling the white phosphorus, the investigations have partly been performed with the grenade held under water. This is to prevent spontaneous combustion of the investigated grenades when opening it. The surveys showed that there are no differences in the design of the grenades, when comparing the two manufacturer's products. In contrast, the grenades from the latter manufacturer shows defects that appear to have arisen in production. The X-ray images showed that the grenades from the latter producer had a lower fill rate compared to those produced by Linde kvarnmekaniska. This means that the supply of air is greater in the newer grenades. The observations indicate that the filling of the phosphorus in the grenade may have been carelessly done, resulting in splashing of phosphorus in the grenade cover. These splashes has reacted with oxygen and moisture in the enclosed air and the amount of phosphoric acid which is formed in some cases caused corrosion through the grenade casing. Subsequently, the grenade started to leak, and the resulting phosphoric acid has harmed other grenades in the container.