Hydrostatic certification is the standard test required every five years for compressed gas canisters used by divers, fire departments and medical personnel, among others, to be requalified for use. This testing is required by federal law and governed by the U.S. Department of Transportation.
The integrity of the pressurized container is checked to ensure no leaks are present and the integrity of the canister is capable of maintaining rated pressure.
Each enclosed tested container is placed in a sealed vessel and water or air pressure is applied to the container from within the jacket. The sealed vessel is pressurized to five-thirds of the amount of pressure for which the tested container is rated. For example, 5,000 pounds per square inch (PSI) would be applied to a container rated at 3,000 PSI of pressure to ensure integrity.
All containers must have pressure-relief devices installed capable of relieving the entire container. Containers may not re-qualify for their specific usage if the compressed gasses would damage or chemically react with the holding tank or otherwise cause the gas to leak from the container. Markings used to identify enclosed hazardous materials must also be legible.