Multiple structure fires sparked by suspected gas line failure in towns north of Boston 7

[bimr]

Authorities ordered residents to leave their homes immediately after dozens of house fires broke out in a string of communities north of Boston Thursday evening.

The Massachusetts State Police were evacuating multiple neighborhoods and restricting access to the area.

"Residents in the affected towns of Lawrence/North Andover/Andover who have gas service from Columbia Gas should evacuate their homes immediately if they have not already done so," state police tweeted.

"Gas lines are currently being depressurized by the company it will take some time."

Link

 

[RVAmeche]

From reports there's been numerous residential boiler explosions and subsequent fires. Something like 75 fires and 30,000 people being evacuated? What could cause a gas like to overpressurize?

​

 

[msquared48]

Fsilure of a large pressure regulator...

Mike McCann, PE, SE (WA)

 

[jojoyohan]

If it was the failure of a regulator, shouldn't there have been a relief device to protect the piping downstream? The relief device could have failed as well. I know the HAZOPs I participate in at my current company would not have discussed multi source failures.

 

[pmover]

pressure regulating stations off pipelines do have PRVs.
from experience, if any work was done and involved cutting, welding, grinding, etc. of metal pipe and those metal shavings got to relief valve such that the sensing tube/pipe was plugged . . . use your imagination.
i saw a fuel pressure gauge "appear" to exceed 300-psig in a class 150 system design to 150-psig. PRV was not relieving and the good ole red button was depressed. weld slag was the culprit.
sand in newly installed fuel gas pipe was another situation.
this goes back to inspection during construction . . ., etc.

 

[jhardy1]

According to press reports:

"The Massachusetts Emergency Management Agency blamed the fires on gas lines that had become over-pressurised, but officials who responded to the area were still investigating the cause.
State officials said Columbia Gas was working to ease pressure on gas lines following the fires. Columbia had announced earlier in the day it would be upgrading gas lines in neighbourhoods across Massachusetts, including the area where the explosions happened.
It was not clear whether work was happening there on Thursday, and a spokeswoman did not immediately return calls."

http://www.abc.net.au/news/2018-09-...injure-four-and-spark-fires-in-homes/10246188

http://julianh72.blogspot.com

 

[Mbrooke]

I know little about gas distribution, my area of interest is in T&D, but I think the gas company either did several things wrong, or we need to re-think how gas is distributed. Of course my opinion is worth nothing- but still scary and mystifying at the same time.

 

[John R]

Scary. If I had gas piped into the house (which I do not, I live in a rural area with no gas distribution) I would install a PRV in the line well outside of the house and point the relief pipe away from any combustible materials. An elevated relief pipe similar to those at vehicle gas stations.

 

[EdStainless]

There is provision for HP relief at my meter, outside of my house.
I know because my failed once (not from HP but from age).
They continuously upgrade the regulators and meters. In WI they consider them to have a 20yr service life.



= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[dgallup]

I've seen systems where the PRV does not have enough flow area to limit the pressure in the case of something like a complete pressure regulator diaphram failure. The PRV is adequate for a small tear or a stuck regulator but not total regulator failure. In that case the pressure goes up very fast.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[bimr]

Gas distribution systems operate at lower pressure during off season. In the fall, the pressure in the system is increased to deal with the expected heating loads. Something must have gone wrong with the pressure increasing procedure.

 

[zeusfaber]

If I was engaged in Homeland Security, I'd be paying close attention to this event and firing up an urgent gas infrastructure security review. No suggestion (yet) that this was an act of terrorism, but too many people will have had their eyes opened to new possibilities for creating "a spectacular".

A.

 

[Spartan5]

I am not normally one of those "I wish the media would stop saying..." guys. But I wish they would stop reporting that "authorities have stated that they believe this was caused by a gas leak."

It's not possible for dozens of fires, miles apart, to be caused by a singular gas leak. C'mon, guys =)

 

[LionelHutz]

Oh, they're stupid enough to believe that work being done + gas explosions = gas leak.

It is scary though. It makes a point that having a gas backup generator isn't always the greatest idea.

 

[davefitz]

We will have to wait for the failure analysis to be completed, but there are several possiblities. The interstate gas pipeline may be operating at 900 psig ( 60 bar g), but the pressure reducing station may reduce that to a consumer supply line ( AT CITY GATES)of less than 30 psig ( 2 bar g) and the household distribution line may be less than 0.7 psig. There typically are no releif valves to atmosphere, and the 900>>30 psig and the 30>>1 psig pressure reduction must be arranged as dual independent pressure regulators in series and with a fast acting shutoff valve that can close within 1 second when a hard wired pressure switch indicates an overpressure had occured. The pressure switches must be calibrated every 6 months, and the concept of "independent " pressure reduction must be interpreted strictly, implying that the power supply and the pressure sensing that operates the PRV must be completely independent from themselves.

Some possible errors might be: (1) possibly converted the PRV to a digital control sytem DCS operated control valve, and the DCS for each valve was common, which violates the independent requirement.

(2)Likewise a DCS control system can be hacked or malprogrammed. A similar error occurred in 1999 near seattle ( bellingham) and the failure was initiated when the the DCS hot-switched to a backup server, and such a "bumpless transfer" had failed the valves to a failed-closed position. The resulting "waterhammer" pressure-pulse burst the pipe.

(3) the pressure swich was not calibrated on schedule or it was plugged by particlulate condensation.

(4) the city gate PRV setpoint may have been incorrectly specced based on PSIG instead of inches water.

(5) the fast closing stop valve stem may have binded up due to corrosion as it might not have been stroked in over 20 yrs

(6) and a dozen other possibilities.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[waross]

My house service regulator (30>>1 psig pressure reduction) has a safety PRV built in.
The few that I have installed on propane service also had a built in PRV.
Are there jurisdictions that allow a final pressure reduction without a Pressure Relief Valve?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bimr]

AGA - How Does the Natural Gas Delivery System Work

 

[waross]

Is it possible that some condensable gas was introduced into the distribution system?
I remember a red-neck butane installation that use cheap undersized final pressure regulating valves without a PRV function.
Tank pressure butane was fed directly to the final PRVs. The tank was in the direct sunlight and the supply pipe ran in the shade. Butane condensed to a liquid in the common supply line.
When the appliances in the new commercial kitchen were started they worked well for a few minutes.
However the regulating valve acted as an expansion valve and got very cold. Then the low temperature caused the reducer to seize
In the full flow position. For several seconds the flame on the stove top would be 2 or 3 feet high. Then the flow of liquid butane would warm the valve and it would work normally for a minute or so.
That's when I was called in.
Three cook tops were doing this at random but frequent intervals.
The solution was twofold; Install an intermediate regulator at the butane supply tank and install a larger regulating valve at each appliance with a built in PRV vented outside.

Is it possible that the failure of an upstream regulator could supply enough volume to the homes that the individual PRVs were overwhelmed?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davefitz]

Yes, condensation of "heavy hydrocarbons" is possible ( C6+), espescially immediately downstream of the pressure reducing valve.For this reason the pressure switches should be protected from such condensibles. It may be a problem for those systems that are recieving "rich LNG" from western africa or facilities that recieve insufficiently processed frac gas.

The news reports are consistent with an issue with the City Gates pressure redcuing station, and an overpressure of the consumer supply piping would explain failures of the household pressure regulators, bursting their diaphrams. Other nes reports indicated that this system of consumer supply pipes are being upgraded and the field construction activities may have compromised the pressure control of the network.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[waross]

Thank you for your reply davefitz.
I have observed over the years that most systems have some inherent redundancy whether in regards to mechanical redundancy or in regards to redundancy in operating procedures or normal practice.

The news reports are consistent with an issue with the City Gates pressure redcuing station, and an overpressure of the consumer supply piping would explain failures of the household pressure regulators, bursting their diaphrams.

That makes sense. The first failure of an upstream regulator led to a second failure of local devices which in turn could overwhelm the local Pressure relief Valves and allow higher pressure gas to flow to the appliances.
I wonder if we will find that the system was originally designed with redundancy but repair work led to a back up pressure relief system being temporarily being disabled, leaving a single point of failure, the pressure regulator which failed.
That is probably more likely than a non-condensible gas issue.
If there was a single point of failure, could a similar failure happen on other systems, Continent wide?


Bill
--------------------
"Why not the best?"
Jimmy Carter