How Can Over-pressure of a Gas Main Cause a Fire/Explosion in a House?

I was wondering the same thing myself....there are so many safety measures it's hard to imagine how this could happen....

http://puc.sd.gov/commission/PSOT/Presentation/regulatoroverview.pdf

..."While transmission pipelines may operate at pressures over 1000 psi, distribution systems operate at much lower pressures. Some gas mains (2 to 24 inches in diameter) in a distribution system may operate up to 200 psi, but the small service lines that deliver gas to individual homes are typically well under 10 psi."...

http://pstrust.org/wp-content/uploads/2015/09/2015-PST-Briefing-Paper-02-NatGasBasics.pdf

I've never heard of such a thing....except in the movies...

I suppose some moron could have piped high pressure directly to the low pressure lines, but who could possibly be that stupid....and there would have to be no safety release valves operating....which would be a violation of safety protocol...

..."It remained unclear Thursday night what caused the succession of explosions across the Merrimack Valley, but the sporadic fires in Lawrence, Andover, and North Andover were likely the result of excess amounts of natural gas coursing through the region’s old pipes, some of which were being upgraded this week.

Officials at Columbia Gas, which provides natural gas to most residents in the region, said in a statement on Thursday that they would be working on their pipelines in the area to improve reliability and add safety features.

But officials at the utility, which is owned by the Indiana-based NiSource Inc., declined to comment on the cause of the explosions.

“We’re still gathering information,” said Ken Stammen, a spokesman for the company."...

https://www.bostonglobe.com/metro/2018/09/13/explosions-cause-unclear-but-specialists-point-gas-pressure/1EyRYFCahN7rZbqodpSxBM/story.html

This is the only kind of thing I've heard of...

https://www.pipeline-conference.com/abstracts/example-effect-sudden-overpressure-piping-system

..."A Pipeline Connected to a Gas Source that could exceed MAOP as the result of Failure, must have Relieving or Limiting Devices meeting §192.199 & §192.201...

From Wikipedia:

A pressure regulator relies on a smooth sealing surface that the poppet lands on to stop further flow to happen downstream. If debris interferes with the seal or a rupture anywhere in the high-pressure line happens then gas can invade. If the pressure is too high one can induce a resonance between the metallic and gaseous springs that repeatedly open and close a regulator.

At least that's WAG using some control theory.

My initial hypothesis is that a sudden spike in the supply pressure, or resonance, as you mention, could cause the regulator diaphragm to rupture. this would allow the control valve to open fully allowing full line pressure to reach the house, and in addition , allowing the gas to escape through the atmospheric side vent. If the regulator was located within the structure and there was an ignition source, than,....BOOM!

Debris and lack of oversight/monitoring of pressure are the likely culprits.

These lines were recently, "maintained/changed" or somehow modified by the gas pipeline people and that is a sure sign of introducing crap into the system.

Improper flushing/cleaning/filtering by the crews and other unknowns will come to light, if not hidden by the gas company.

These homes may be near a branch from a larger line or near the termination of a line, all of which might have collected the debris.

It wasn't an accident.

Isn't it possible that some of the customer pressure regulators might fail to withstand the higher input pressure, passing higher pressure to the customer gas lines and appliances and causing leaks?

I replaced some gas lines in a house once before I had the gas turned on. To test the connections I pressurized the system with air, I forget what pressure I used but it wasn't that high. I was surprised to hear pressure leaking from the seal on the meter and confirmed with soapy water.

When I had the gas turned on at the house I mentioned to the person that I thought my meter was leaking. They turned on the gas and tested it and nothing leaked, they ended up replacing the meter anyhow since it was out of date.

From that experience I don't think the meters themselves can withstand much over pressure if a regulator failed even if the appliances could. Many meters are located inside.

"From that experience I don't think the meters themselves can withstand much over pressure..."

Specifically I would suspect the bellows in the meter housing.

The surprising thing is that if sufficient gas collected to cause these explosions, and the gas was odorized as required in many municipalities, at least one person should have smelled it; I recall many years ago visiting a local gas company facility, and smelling the odorant (ethyl mercaptan) in a closed container over 100' away!

That is a good point. I took a look at my gas meter (fortunately located outside my house). The meter nameplate rated the meter at 5 PSI. However, the meter is located on the low pressure side of the pressure regulator, again pointing to the regulator as the primary point of failure.

Lyn made good point that the recent work on the mains may have caused debris to enter the lines. Particulate debris may have entered the regulators on the effected homes and prevented the valve from seating completely.

Finally, the incident happened late in the afternoon, between 4 and 5 PM, just when most people were returning home from work.

The local government (mayor I think) has declared a SOE and brought in a different utility to oversee the clean-up and help with the investigation. (NPR) I heard this while riding my bike, details sketchy.

Massachusetts explosions: Owner of Columbia Gas linked to three prior gas line blasts

Explosions, fires north of Boston that killed one, injured at least 25 were at least the fourth tragedy linked to Columbia Gas of Massachusetts owner.

USA TODAY 5 hours ago bookmark_border share more_vert

'Particulate debris may have entered the regulators on the effected homes and prevented the valve from seating completely.'

No strainer / filter required?

I was just elaborating on #2 from redfred

While I've heard of gas explosions before, this is the first time it's been attributed to overpressure.

Usually it's because of a crossbore- the utility installs new lines with directional drills, and somebody goes though a sewer near someone's house. After a while the line catches too much cr4p and plugs up the sewer, so they call in a plumber and he sends his rooter down to clear it out. You can guess the rest...

Similar thing happened a few years ago in Kaoshiung - southern Taiwan

https://www.youtube.com/watch?v=VxyjGNq0y5U

But this was an explosive disassociation of a chemical, IIRC -

Russian conspiracy - Vladimir had just replaced some meters at the home...

There are two links in the chain

The first is the definition of overpressure, which is a pressure that the containing structure is not strong enough to withstand. That causes a leak.

They second link is a source of ignition. The only free thing in this world is a source of ignition.

Once one has a leak and a source of ignition a fire is a likely outcome.

One of 60 fires and explosions...

https://www.cnn.com/2018/09/15/us/massachusetts-explosions-fires-gas-pipeline/index.html

Not familiar with gas, but for multiple locations to be impacted basically simultaneously (relative to 50 years operation) there is some "common cause".

I had remarked to a friend over here about grease and acetylene and wondered whether a lubricant had been used while fitting a new valve or some other service part that had been maintained that day.

Just wondering whether this gas reacts with lubricants and ignites on exposure to atmosphere.

Natural gas is primarily methane with just a bit of ethane....I don't know of any thread sealants or lubricants that react with NG....

https://en.wikipedia.org/wiki/Natural_gas

Something similar happened in Royston, Hertfordshire UK in 1991

http://www.hertsmemories.org.uk/content/herts-history/towns-and-villages/royston/great-gas-crisis

..."On Friday the 8th March 1991, Royston made national news headlines when it was rocked by numerous fires and explosions caused by a gas surge. Human error had led to the network of high pressure gas which carried gas supplies between towns being connected directly to the network supplying Royston houses. This link resulted in a massive surge of high pressure gas entering the system in the town at approximately 5.15pm....

...The town was inundated with British Gas vehicles and engineers, the Meridian School became a control base for the repair operations and the Little Chef restaurant was used by the engineers for refreshments. Eastern Gas called on over 200 engineers who had to inspect every building which used gas. Every meter in town had to be changed...

...Calls were made for a public inquiry in to the incident but this was not granted. The Health and Safety Executive (HSE) undertook a full investigation and published their findings. The HSE’s investigation revealed that the root causes of the incident were: a) errors in describing and identifying the work to be done; b) further errors in the method of installation and commissioning, and deviation from normal declared practice, which led to the original errors not being detected; c) a lack of adequate communication between individuals to allow faults to be detected....

....The accident could have had very serious consequences to life and limb, and following its investigation HSE prosecuted British Gas plc for breach of the Health and Safety at Work etc Act 1974. It became apparent as the case progressed that HSE would not succeed under the current interpretation of the law in establishing that any shortcomings in the procedures of British Gas, or in the way its employees had carried out their jobs amounted to a criminal offence on the company’s part, and the case was therefore withdrawn...."

'The HSE’s investigation revealed that the root causes of the incident were: a) errors in describing and identifying the work to be done; b) further errors in the method of installation and commissioning, and deviation from normal declared practice, which led to the original errors not being detected; c) a lack of adequate communication between individuals to allow faults to be detected....

....The accident could have had very serious consequences to life and limb, and following its investigation HSE prosecuted British Gas plc for breach of the Health and Safety at Work etc Act 1974. It became apparent as the case progressed that HSE would not succeed under the current interpretation of the law in establishing that any shortcomings in the procedures of British Gas, or in the way its employees had carried out their jobs amounted to a criminal offence on the company’s part, and the case was therefore withdrawn...."

Anything but tell you the actual cause. Typical bureaucrats.

"...and the case was therefore withdrawn...."

...and nobody held accountable....criminally that is....that does not preclude civil liability...

"At its simplest, civil liability means being responsible for actions and practices that could damage others, but which aren’t criminal. So they’re not pre-meditated or against the law.

Instead, civil liability concerns the times when there isn’t any intention to cause harm, but harm occurred anyway. If you’re a business owner, that might mean having a faulty piece of equipment that injures someone. Or doing a piece of work that’s judged not up to scratch.

In cases like these, the person affected might decide you bear civil liability for whatever’s gone wrong, and try to claim damages. And that can leave you open to some pretty hefty compensation payments, not to mention legal costs.

It doesn’t end there either, because we’re not just talking about your defence costs. If you end up on the losing side, you’ll have to pay the claimant’s expenses too."

https://www.policybee.co.uk/blog/13454/what-is-civil-liability

Massachusetts Gas Lines Had 12 Times the Recommended Pressure Before House Explosions

Columbia Gas faces investigations, senatorial questions, and at least one lawsuit following the disaster.

But why only certain residences? Wasn't the entire system being replaced and tested?

I would guess that those residences that burned still had pilot lights.

...but the pilot lights are still within the main burner section, I don't see how that could cause an explosion....It seems more likely to me that there might have been leaks existing already and the higher pressure increased the volume of gas being leaked....now natural gas is unlike propane in that it is the same weight as air, and mixes freely....so a still setting or protected area for the gas to accumulate it seems would be necessary, that then coupled with a source of ignition, probably an A/C unit, as gas mains are usually located nearby...5ft min by code...

Fine. You cannot see at all how the only commonly not valved OFF gas line (a pilot light) could with over pressurization fill a large enough space containing air to achieve an explosive mixture.

I must be deluding myself.

Well in my experience the pilot light is valved off by the gas valve, it is the thermocouple that when heated by the pilot flame generates the voltage to open the pilot valve....Now unless you're going back to the early 1900's or something, I must confess I am not aware of any of these still existing...not saying it isn't possible...

That doesn't sound like a fully correct explanation.

You do realize how long Boston has been a city? The stove, oven, water heater, clothes dryer and furnace installed in my childhood 1960's era house all had pilot lights. The 0.5 PSI pressure level downstream of the regulator meant nothing more than a nuisance having to relight a blown pilot light. Now a debris failing regulator with 12 times the expected mains pressure blowing through it then a lot more gas could blow probably the pilot flame out with a lot of gas until...

How do you heat your house in Florida?

Well I have electric heat but I'm a retired HVAC mechanic and have worked on gas appliances up and down the east coast for over 30 years....I've sold, serviced and installed every kind of gas appliance, heater and boiler there is....All gas lines are installed with sediment traps to catch any debris in the line....

https://structuretech1.com/sediment-traps-what-and-why/

Wonderful! I made a layman's guess explaining how these homes could be destroyed by a utility performing a maintenance procedure. Can you, with your experience, come up with a better-informed explanation? You already mentioned that over-pressurization would be needed and that has been found to be true. I realize forensic data is not at your disposal and so the best we can expect is just a plausible explanation.

I suspect the pressure relief valves failed due to poor maintenance....or poor system design....Followed by gas line failure due to poor maintenance and age...

https://asgmt.com/wp-content/uploads/2016/02/002.pdf

Look at the picture in (your) post #28. Explain how the sediment trap protects that pressure reducing valve. The incoming line on left is probably at about 5 PSI. The regulator output is probably about 0.5 PSI. If dirt on seat of PRV (and this would only occur at random locations, not necessarily all) the lines in meter and house reach (if not much gas being used) 5 PSI. This can greatly exuberate small leaks that might not have even been noticed before. Might even blow out the combination gas valve's diaphragm.

The pilot lights on gas appliances are protected from this type of failure. The main control valve controlling gas to the pilot and the main burner has a thermocouple positioned in the pilot flame. If the thermocouple does not detect the flame, then gas flow to both the main burner and the pilot will be shut off.

Maybe pilot lights as redfred said, or more likely a sparking electrical contact.

We may never know.

Let's be glad the entire towns didn't explode.

gas + oxygen + spark = boom

(details may vary in your locale)

This happened just a few miles from where I lived back in 1985....It was a Midas Muffler shop that had a propane gas leak in the shop, when they came in for work in the morning, not sure but think someone was smoking, and BaBoom the entire building was leveled, all that was left was the slab and the flagpole with the flag still intact....

http://articles.sun-sentinel.com/1985-09-25/news/8502100346_1_propane-tank-midas-muffler-blast

That proves that smoking is bad for your health.

America's Oldest Man, Age 112, Smokes A Dozen Cigars A Day

This proves smoking is good for your health....

No! Not cigars. I smoke cigars!

Or in this case turning on the lights at start of day in a gas filled building might have been bad for someone's health.

The Boston blast was natural gas. Your Midas Muffler blast was propane.

NG is lighter than air and dissipates quickly while propane's heavier than air will lay on the floor waiting for the spark.

Both need enclosure, both make big Boom..

.

That's an annoying, possibly lethal boom, but not a big boom.

These are big booms.

It's not the size but the proximity that matters.....