A partial pressure sensor for an automated gas environment system (AGES) was not functioning correctly for pure hydrogen flow. While personnel were troubleshooting the problem, a burst disk ruptured resulting in a leak of hydrogen gas and actuation of a flammable gas alarm.

System troubleshooting involved the installation of a small hydrogen gas cylinder and temporary manual valve in an engineered ventilated enclosure adjacent to an instrument sample well. A burst disk associated with the temporary manual valve ruptured upon opening of the gas cylinder valve. The vented gas, exhausting through an engineered exhaust system, triggered the flammable gas detector. Personnel promptly evacuated the area in accordance with established procedures. Appropriate personnel responded to the event, established a safe condition and made appropriate notifications. There were no injuries or other environmental, health and safety impacts associated with this event.

The ventilated enclosure, a hazardous gas cabinet, is designed to contain and exhaust hazardous gases from the building should a leak develop during the conduct of experiments. Input gases are normally fed into the cabinet from an outlying cylinder shed. The external line to the hazardous gas cabinet enters the cabinet and connects to a three-way block. The output of the block connects to a regulator that feeds the gas flow control system. The "spare" third block connection is normally plugged.

For testing, a small bottle of ultra-high purity (UHP) hydrogen gas was installed into the hazardous gas cabinet. The bottle was connected to the "spare" third block connection through a high-end manual valve. The input from the cylinder shed was manually isolated. The temporary manual valve could be opened to facilitate evacuation of atmospheric gas contaminants prior to opening the clean bottle of hydrogen, thus ensuring system integrity.

Temporary modifications to the AGES system were documented in an approved test plan and on a "red-line" of existing, approved process and instrument diagram (P&ID) drawings. During the testing, system as-built drawings were being re-verified and details discovered during testing documented within the test plan.

SUMMARY OF IMMEDIATE ACTIONS TAKEN:

- Evacuated the immediate area.

- Gas bottle isolated and testing suspended.

- Responding personnel verified conditions safe for reentry.

- An investigation was initiated and critique conducted on the following day.

DISCUSSION OF CAUSE: The temporary manual valve selected for testing of the automated gas environment system (AGES) had an integral burst disk rated at 1900 psi +/- 100 psi. This is an unusual valve configuration, typically used for cryogenic service. The valve was an on-hand spare, but the documentation of the burst disk feature was not available. It was not recognized that the burst disk was an integral part of the valve. The pressure in the small UHP hydrogen bottle was approximately 2015 psi. The regulator downstream of the gas bottle is rated for 3000 psi input, so it could accommodate the bottle's supply pressure. The direct cause of this event was the improper selection of the manual valve with integral burst disk rated below the bottle supply pressure for this temporary testing configuration.

Personnel were focused on the AGES system test and results, not the compatibility of the test equipment. The manual valve was needed to successfully test the system, however the fact that this particular valve could not accommodate the full cylinder pressure was overlooked.