Gas release makes a real stink
A distinctive rotten-egg like odor pervading downtown Wednesday afternoon came from a pressure release valve in west Hillsboro venting natural gas into the atmosphere.
The foul odor continued to drift on the prevailing east winds for about 45 minutes. Routine maintenance on a nearby pipeline caused a buildup of pressure in smaller distribution lines, causing the valve to activate, said Northwest Natural Gas spokeswoman Jenna Cooper-Gross.
Such designed releases are rare, but not very dangerous, she said. The overpressure valve is a safety device to prevent the failure of the smaller lines.
“The unit acted exactly as it was designed to do,” Cooper-Gross said. “In this case, it was loud and smelly.”
The smell did not come from natural gas — which is odorless — but from mercaptan, a telltale chemical added by gas companies to detect leaks.
Cooper-Gross said mercaptan is heavier than air while natural gas is lighter than air. During a pressure relief venting, the mercaptan tends to drift around the neighborhood while the combustible vapors move upward.
Several residents living around the valve near Northwest 317th Avenue and Northwest Jackson Street called 911 at about 3:30 p.m. to report a loud sound and a strong odor. Hillsboro police and fire crews responded, evacuating a three-block area for about two hours as a precaution.
After residents and businesses further east began reporting the smell, a reverse 911 message was sent out that gas readings on the ground were minimal, said Hillsboro Fire and Rescue spokesman Storm Smith.
Northwest Natural crews were able to resolve the situation by 5:24 p.m., and the smell began to dissipate. Homes nearby were checked for gas before residents were allowed back in.
Cooper-Gross said the gas crews took appropriate action, allowing the pressure valve to vent until it reached its lower level of pressure and it would close on its own.
Back Pressure Valve - News
Homes nearby were checked for gas before residents were allowed back in. Cooper-Gross said the gas crews took appropriate action, allowing the pressure valve to vent until it reached its lower level of pressure and it would close on its own.
Electrical Valve, a fully variable backpressure control valve, which enables vehicles using low-pressure exhaust gas recirculation (EGR) systems to minimize NOx emissions. Installed in the exhaust systems downstream from the diesel oxidation catalyst
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Burst supply hoses however are more common and they have the potential to cause significant damage. When the supply valve is open, the hose is under pressure. A failure in the hose at 70 pounds pressure can release as much as 650 gallons an hour.
The red finding was issued when a low-pressure coolant injection valve failed to open last October. The finding also placed the plant in a “multiple/repetitive degraded cornerstone” category. At a public meeting in Atlanta, officials with the NRC said
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