Abstract: A safety device for vessels of compressed gases is disclosed which comprises a cap enclosing the valve of the vessel, a port formed in the wall of the cap for passing a nozzle attached to the valve, a handling member for rotating the handle of the valve from outside of the cap, a purge gas introducing and exhausting ports formed in the wall of the cap, and a detector disposed in the middle of the exhausting pipe coupled to the purge gas exhausting port. The handling member comprises a shaft vertically extending through and slidably supported by the ceiling of the cap, a horizontal disk secured to the lower end of the shaft, and four circumferentially equally spaced vertically extending fingers fixedly secured to the circumferential portion of the lower surface of the disk, which disengagably engage with the grooves formed on the circumference of the handle.