Presumably there would be both the precaution that the compressor would have a shut-off when the cylinder reaches a maximum pressure, and the cylinder itself would have a feature such as a burst disk. But if the condition of the metal in the cylinder was such that it lost integrity at a lower pressure than the shut-off or burst disk were set for, it could explode at some other point of the cylinder that had been weakened for some reason such as corrosion. For the answers to whether these safety precautions were in place as well as to the condition of the cylinder, we will have to wait for the result of the investigation, I'm guessing.