Hydrogen leak detection systems may be required by the Authority Having Jurisdiction (AHJ) or may be installed as a means for enhancing safety of the operation. Leak detection can be achieved by providing hydrogen (or flammable gas) detectors in a room or enclosure, or by monitoring the internal piping pressures and/or flow rates for changes that would suggest a leak is present in the system. Other methods include providing detectors in close proximity to the exterior piping or locating hydrogen piping within another pipe and monitoring the annulus for leaks.
Regardless of the method used, leak detection systems should, at a minimum, incorporate automatic shutoff of the hydrogen source (and startup of a properly-configured active ventilation system, if present) when hydrogen is detected. For systems designed to monitor hydrogen concentrations in rooms or areas, the leak detection system should also warn personnel with visual and audible warnings when the environment is becoming unsafe. Remote notification should also be considered.
Goals for an area hydrogen leak detection system include:
- Detection sensitivity of +/-0.25% by volume of hydrogen in air
- Response time of 1 second at a concentration of 1% by volume
- Detection range of 1% to 10% by volume of hydrogen in an inert atmosphere
The design of a leak detection system must ensure that any leaking hydrogen would pass by the detector. Consider using a hood to route leakage across the detector.
The sensitivity of the detector to other gases and vapors should be considered in the selection of the detector and should be explained to personnel. Additionally, caution should be exercised when selecting and using detectors that may themselves be ignition sources.
A good practice is to set the detectors to alarm at 1% hydrogen by volume in air, which is 25% of the lower flammability limit (LFL). If automatic shutdown is incorporated into the system, manual reset should be required to restart the system.
Portable gas detectors are valuable for local leak detection. Portable detectors should be used for entry or re-entry into rooms in which an alarm has occurred to ensure that the hydrogen has dissipated.
Maintenance and recalibration of leak detectors should be performed every 3-6 months and recorded in facility records or manufacturer's instructions.