Abstract: An improvement in chemical cutting apparatus for use down within a well bore comprising improved means of discharging a cutting agent in conjunction with an automatic means of pressure relief. The relief also includes an expendable plug and an "O" ring assembly, which acts to prevent clogging of the relief port prior to firing of the cutting apparatus. The pressure relief is made small enough and is so located to prevent it from interfering with the normal operation of the cutting tool, but nonetheless is effective in relieving the built-up high internal pressure when the tool malfunctions. The improved means of application of cutting fluid includes a discharge/containment sub assembly which contains means of driving the cutting agent from the assembly via a piston actuation arrangement.