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The Case of the Exploding Propane Regulator

Pre-set Secondary Pressure RegulatorThe Problem:

The purpose of the pressure regulator in a propane system is to control the flow of gas and lower the pressure from the tank to the appliance.  Propane tank pressure can be 200+ ounces psig.  Residential regulators can reduce the pressure to 6.3 ounces psig.  The propane regulator’s purpose is to create a "bottleneck" and reduce the gas pressure to a safe and usable level.  When the regulator vent is plugged and not open to the atmosphere, the regulator cannot operate properly and will malfunction.

My Assessment: 

Pressure Regulator SchematicIn a pressurized gas system, the propane regulator vent must remain open to work properly.  Freezing rain is a common reason for vent blockage. If the vent does become plugged, it will not be able to work properly.  When plugged, it could allow high pressure gas to reach the appliance, or the appliance pilot light could be extinguished. Either instance could result in an explosion or a fire.  Failure to follow the manufacturer’s instructions and warnings could result in personal injury or property damage.

The Consequences: 

When examined in the WJMG laboratory, the vent was plugged.  High pressure propane gas entered the building through extinguished pilot lights.   The unburned propane gas resulted in an explosion and a fire. 

Adjustable Pressure RegulatorsThe Lessons Learned: 

All domestic regulators must have “drip lip” style vents. These units resist plugging by freezing rain when installed with the vent pointing vertically down.  When it’s not possible to point the vent vertically down, a hood or encasement should be used to keep the vent open to the atmosphere.   All vents should be kept open to permit free flow of air into and out of the regulator.  Vent openings should be protected against the entrance of rain, snow, ice, paint, mud, insects, or any other foreign material that could plug the vent.

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Welding Failures I Have Known, Interesting cautionary tales from Metals & Welding  expert, Dr Jesse A Grantham, PE