
NTSB Report: Over-Pressure of a Massachusetts Natural Gas Distribution System - mkeeter
https://www.ntsb.gov/investigations/AccidentReports/Pages/PLD18MR003-preliminary-report.aspx
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danielvf
The gas lines here used a different system than most of the US. The normal way
is for a high pressure line to run to a regulator at each house. That
regulator then controls a low pressure for that house alone.

This gas company however had low pressure distribution lines connected to
thousands of houses, each controlled by a single regulator and operating at
0.5 psi.

While replacing a section of distribution piping, workers left the pressure
sensors the regulator used attached to the old piping. This caused the
regulator to continue raising the pressure in the new piping since as it was
fed data that pressure in the old piping was falling to zero.

The fault was with the work plan order, which the workers on the scene were
following exactly, and with a system design that allowed a single point of
failure to burn a hundred houses. The gas company will be switching this area
over to a more normal setup with regulators at each house.

~~~
dsfyu404ed
Those houses shouldn't have burned let alone had gas explosions. Appliances
should be able to take a pressure spike well into the double digits (if you've
got something in the oven it might come out a little crisp though). The
typical steel piping found in homes should be good well into triple digit
pressures (as should any copper or soft line). The problems that caused this
aren't just constrained to Colombia Gas property.

------
dsfyu404ed
<tl;dr>

As part of routine work some pressure sensing equipment was erroneously
disconnected from the gas main causing it to read low causing more pressure to
be supplied to that main (which the disconnected sensors obviously didn't
register). Alarms were triggered but there was no system in place to
automatically shut the line down or bleed pressure so no corrective action was
taken until after a few houses blew up.

</tl;dr>

<rant>

What I really want to know is why certain houses had gas explosions and others
didn't. It's basically an open secret in MA that most plumbers are terrible
and do the bare minimum because our laws force anyone seeking to follow the
law to give them business. If poorly executed residential gas plumbing was a
contributing factor it would be nice to see at least one person responsible
raked over the coals for hand tightening gas pipe (which many of them do
because "it doesn't even need to hold one pound of pressure").

</rant>

