In 1930, over of liquid oxygen were used for this purpose in Germany alone, and additional 201,466 lb (91,383 kg) were consumed by British quarries. The accident rate was lower than with conventional explosives. However, the Dewar flasks the LOX was stored in occasionally exploded, which was caused by iron impurities in the activated carbon serving as trace gas absorbent in the insulation vacuum layer in the flask, which caused spontaneous ignition in case of LOX leak into the enclosed space.