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Old 10-11-2018, 05:22 PM
 
2,350 posts, read 595,169 times
Reputation: 3007

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The NTSB released a preliminary report today.

Missing instructions caused deadly gas explosions, NTSB report says


Quote:
Inadequate planning and instructions led to a Columbia Gas contractor over pressurizing a distribution system in the Merrimack Valley and causing a series of explosions and fires that killed one person and left dozens injured, according to an initial review from the National Transportation Safety Board.

Minutes before the explosions sparked widespread evacuations and left three towns reeling, an alarm went off in the Columbia Gas Monitoring Center in Columbus, Ohio. What’s called a low-pressure gas system in South Lawrence was suddenly over pressurized.

At 4:04 p.m., monitoring crews in Ohio knew something was wrong, but they weren’t able to manually open or close the valves, the NTSB report notes.
https://www.ntsb.gov/investigations/...ry-report.aspx
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Old 10-11-2018, 06:18 PM
 
Location: Somerville, MA
885 posts, read 712,123 times
Reputation: 1042
Quote:
The contracted crew was working on a tie-in project of a new plastic distribution main and the abandonment of a cast-iron distribution main. The distribution main that was abandoned still had the regulator sensing lines that were used to detect pressure in the distribution system and provide input to the regulators to control the system pressure. Once the contractor crews disconnected the distribution main that was going to be abandoned, the section containing the sensing lines began losing pressure.

As the pressure in the abandoned distribution main dropped about 0.25 inches of water column (about 0.01 psig), the regulators responded by opening further, increasing pressure in the distribution system. Since the regulators no longer sensed system pressure they fully opened allowing the full flow of high-pressure gas to be released into the distribution system supplying the neighborhood, exceeding the maximum allowable pressure.
So they were replacing an old main that had sensors on it. When they disconnected the old main the pressure in that section dropped as it was vented. The sensors were still connected and operational on this old main so they sensed what appeared to be a low pressure issue. This caused upstream regulators to increase pressure to their full output which was much higher than what the neighborhood's system was designed for.

The Columbia work plan didn't involve isolating or relocating these sensors to correctly measure the pressure that was upstream of the work (aka, the houses and other devices not capable of handling the full pressure that was delivered).

Surprisingly, the gas control center couldn't remotely operate valves that would have cut the main off. They needed to dispatch technicians to manually or locally close the valves/regulators. I'm an operator at a power plant and their inability to remotely control that is mind boggling, but that could just be how gas distribution systems work.

Quote:
According to Columbia Gas, all cast iron and bare steel piping in the affected neighborhoods will be replaced due to system integrity concerns. The new system will consist of high-pressure plastic mains with regulators at each service meter to reduce the line pressure from the main to the required pressure.
That is one hell of a project. Right before winter too.
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Old 10-11-2018, 10:08 PM
 
Location: New England
1,932 posts, read 1,074,088 times
Reputation: 1685
I wonder if national grid has the ability to remotely close valves, and that's why there weren't any damages in Woburn.
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Old 10-11-2018, 10:43 PM
 
Location: Somerville, MA
885 posts, read 712,123 times
Reputation: 1042
The Woburn incident involved a crew who was performing routine work at a regulator station. They noticed their error (whatever it was) and were able to fix it quickly.
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Old 10-12-2018, 09:47 AM
 
3,940 posts, read 3,852,295 times
Reputation: 2193
Quote:
Originally Posted by wolfgang239 View Post
So they were replacing an old main that had sensors on it. When they disconnected the old main the pressure in that section dropped as it was vented. The sensors were still connected and operational on this old main so they sensed what appeared to be a low pressure issue. This caused upstream regulators to increase pressure to their full output which was much higher than what the neighborhood's system was designed for.

The Columbia work plan didn't involve isolating or relocating these sensors to correctly measure the pressure that was upstream of the work (aka, the houses and other devices not capable of handling the full pressure that was delivered).

Surprisingly, the gas control center couldn't remotely operate valves that would have cut the main off. They needed to dispatch technicians to manually or locally close the valves/regulators. I'm an operator at a power plant and their inability to remotely control that is mind boggling, but that could just be how gas distribution systems work.



That is one hell of a project. Right before winter too.
This is starting to remind me of Three Mile Island. I thought the lessons learned would have prevented sensors from going down to begin with. Way back in the day my father worked at a place where people were paid to monitor a meter. If the needle dropped or rose by a certain amount to call. That's all electronic now and should be remote. This is like when I was in retail and was asked "Do you remember where the holes were in the roof". Uh there's no reason for me to be on the roof and furthermore I have no way of telling exactly where. Facilities and systems these days are too big to rely on manually closing/opening/turning on or off systems. Infrastructure relies on maintenance. If you don't take care of it then it won't take care of you. Last night a tree came down near me (urban apartment area). Well it turns out there's really no concrete foundation holding this up so the rest of them have to come down as well.
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Old Today, 03:42 PM
 
2,350 posts, read 595,169 times
Reputation: 3007
Thousands of people are still without heat and hot water.

NiSource is now under Federal criminal investigation.
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