A containment vessel is provided to allow the safe, environmentally acceptable release and recontainerization or other processing of hazardous contents from compressed gas cylinders or other target container. The containment vessel is used to position a gas cylinder or other target container adjacent to one or more pneumatic guns. A variety of projectiles are provided for use with the pneumatic guns to pierce the body of the target container. Each pneumatic gun includes a pneumatic chamber within which is developed a secondary force and a gun barrel attached to the containment vessel to fire a projectile which will puncture the target. Connections are provided for communicating with the containment vessel for evacuating and recontainerizing the contents released by rupturing the target without releasing the contents into the environment. All of the gas cylinder processing operations may be conducted remotely.