Hydrogen Leak from Flow Meter

A hydrogen gas detector on the ground floor of a building registered the release of a small amount of hydrogen gas and actuated automatic alarms both at the fire department and in one of its buildings. Additionally, interlocks connected to the gas detector completely shut down the experiment. Upon hearing the alarm, all occupants (about 6) promptly left the building. Fire department personnel are housed in the trailer next to a building and responded within one minute. They tested the atmosphere within the building, reset the gas detector, and secured the alarm at 9:15. The alarm was actuated when an experimenter assigned to the experiment was evacuating lines using a vacuum pump.

The speed of evacuation was controlled by a commercially manufactured flow meter. It is believed that the 0-ring in the manually operated valve had deteriorated and that a small amount of hydrogen gas escaped while the valve was being turned. The flow was set at approximately 1 l/min at a pressure of only 6 psi. The gas detector is located within 30cm of the valve so the time from release to solenoid activation should be less than one second. Using these criteria, it is estimated that the total release of hydrogen gas is less than l cc.

Sufficient testing and investigation has confirmed that a minimal amount of hydrogen escaped around a failed O-ring located in the valve of the commercially manufactured flow meter (direct and root cause). A significant contributing cause is the lack of a stop to prevent the valve from being opened to the point of the O-ring being damaged or distorted by contact with the threads of the valve. The flow meter in question is used only in the gas evacuation process so is opened to it's fullest extent at least daily. Although we have confirmed that no caution against over turning exists in the manuals accompanying the flow meters, we believe that this may have led to premature failure of the O-ring.