A person working in a hydrogen lab unknowingly closed the wrong hydrogen valve and proceeded to loosen a fitting in one of the hydrogen gas lines. The pressure in the 1/4"-diameter hydrogen line was approximately 110 psig. Hydrogen escaped from the loosened fitting and the pressure release resulted in the tubing completely detaching and falling to the floor. The person noted seeing a white stream around the hydrogen jet leak. The person noted a color change and noise change as the leak ignited (this happened in a matter seconds and he did not have a chance to react). The person left the lab and pushed the emergency stop button. Someone else pulled the fire alarm. Both of these actions were designed to close the main hydrogen solenoid (shutoff) valve. The local emergency response personnel realized that the hydrogen supply had not been turned off by the building safety systems and manually closed the main hydrogen valve next to the hydrogen tank farm.
The gas lab safety system has a main control panel. The hydrogen sensors, flame detectors, emergency push buttons, fire alarm and sprinkler system are all inputs into the control panel. In the event of an emergency, if any of these systems are engaged, the control panel should de-energize the main solenoid valve and stop the gas flow. However, this did not happen.
Onsite personnel were puzzled by the fact that apparently all of the safety systems had failed to close the main solenoid valve on that day. The onsite personnel questioned some key individuals on the testing of the emergency systems and found out that they confirmed solenoid valve closure, after activation of safety devices, by listening for evidence of valve movement (click).
The main solenoid valve was removed from the gas line manifold for inspection. It was evident just as it was taken out that the problem could have been due to an installation error. The valve was installed in a horizontal pipe run and 90° from upright. However, the solenoid valve had a marking on one side, which read: "Mount vertical and upright (see instructions)". This marking could not be seen when the valve was in the installed position. An arrow on the valve body showed what was considered to be the correct mounting position. The valve was tested in the upright position and it worked perfectly. However, when the valve was tested as installed (rotated 90° from upright), evidence of the valve stroking could be heard but it did not seal properly.
A new valve was ordered (identical to the old one), and it did not fully close when tested either (even when mounted as per the installation instructions). The new defective valve had to be returned to the manufacturer. To remedy the problem, the laboratory changed their piping configuration to have two valves in series in the system. They also changed their lab safety system testing procedures. Instead of listening for the valve movement to confirm valve closure, they measured the downstream pressure from the main valve as the safety devices were being activated.
Laboratory personnel could not determine with certainty the ignition source, but they suspect it could have been either static discharge or a power bar.
Corrective Steps:
- Place the hydrogen main shut off valve in the correct orientation.
- Change lab safety system testing procedures. Instead of using the valve noise to confirm valve closure, they measured the downstream pressure from the main valve as the safety devices were being activated.
- They also changed the lab working procedures and training to account for the human error.
- Test safety system components even if they are new.
- Do not rely on listening for valve movement as confirmation that a valve is closing; measure downstream pressure to determine if the valve is really sealing properly.
- Lock the valves when working in gas manifolds.
- Maintain a clear path to the exit in case of an emergency.