Cause of those tragic natural gas explosions

Thread Starter

Raymond Genovese

Joined Mar 5, 2016
1,658
Official: Pressure sensors focus of gas explosions probe

NTSB Chairman Robert Sumwalt said the sensors can signal for gas pressure to be increased if the pressure gets too low. He said investigators will try to determine whether those sensors played any role in Thursday’s explosions and fires.

If I am understanding what is being implied here, it sounds like pressure sensors might have called for more pressure increases with no absolute limit?! Being attached to a line that had been disconnected when the sensors were still online could have been the factor?? Is that how you read that? Why wouldn't there be a limit on the called for pressure by the sensor and with an alarm?

I guess we are a ways away from having this explained but I am already puzzled.
 

nsaspook

Joined Aug 27, 2009
7,723
Official: Pressure sensors focus of gas explosions probe

NTSB Chairman Robert Sumwalt said the sensors can signal for gas pressure to be increased if the pressure gets too low. He said investigators will try to determine whether those sensors played any role in Thursday’s explosions and fires.

If I am understanding what is being implied here, it sounds like pressure sensors might have called for more pressure increases with no absolute limit?! Being attached to a line that had been disconnected when the sensors were still online could have been the factor?? Is that how you read that? Why wouldn't there be a limit on the called for pressure by the sensor and with an alarm?

I guess we are a ways away from having this explained but I am already puzzled.
Don't know what happened here but we can look at the past.
https://sma.nasa.gov/docs/default-s...sage-2012-03-05-sanbrunopipelineexplosion.pdf
What happened
Power Replacement and Overpressure
On September 9, 2010, PG&E technicians were dispatched to the Milpitas terminal to replace electronic systems as part of an upgrade to the station’s power supplies. To accomplish the upgrade, the technicians needed to remove power. After doing so, they encountered an unexpected power loss at a local control panel. PG&E did not have a plan for this contingency. Instead of re-energizing the circuit, the technicians tried to reroute power from an alternate source. Their attempts, however, caused erratic output voltages to send an erroneous low pressure signal to the regulating valve controllers, affecting valve position sensors which triggered over 60 alarms at SCADA. The alarms prompted SCADA operators to inform the Milpitas technicians that SCADA’s readings indicated an abnormally high pressure at the Milpitas Terminal. Technicians confirmed that the erratic voltages had sent an erroneous low-pressure signal to the regulator valves, causing them to open fully. To complicate matters, the regulator valves could no longer be controlled because of power loss, so outgoing pressure was now solely controlled by monitor valves—a last line of defense against overpressure. The monitor valves were set to prevent outgoing pressure from exceeding 386 psig. SCADA, however, informed Milpitas that their consoles indicated a pressure of nearly 500 psig on downstream pipelines. At 5:52 p.m. Pacific Standard Time, the operator asked the Milpitas technicians to place a pressure gauge on Line 132. Due to a lag in the monitor valve response time, the resulting reading showed an outgoing pressure of 396 psig—a value below the Line’s MAOP of 400 psig, but well above the MOP of 375 psig. At 6:02 p.m., a SCADA operator called another PG&E monitoring facility and said, “we’ve got a major problem at Milpitas and we’ve over pressured the whole peninsula.”
 

WBahn

Joined Mar 31, 2012
26,272
Can't read the article without paying, so I don't know what it says.

It will be interesting to find out more about this -- hopefully with explanations for why the existing system is the way it is (often times there are very reasonable explanations for stuff that, on the surface, seems stupid). It does seem strange that there wouldn't be limits or failsafes since they have to assume that any given pressure sensor is going to malfunction sooner or later. But it might also be the case that the pressure sensor had nothing to do with the disaster and it's just one thing investigators are looking at among a whole slew of things.
 

Thread Starter

Raymond Genovese

Joined Mar 5, 2016
1,658
Can't read the article without paying, so I don't know what it says.

It will be interesting to find out more about this -- hopefully with explanations for why the existing system is the way it is (often times there are very reasonable explanations for stuff that, on the surface, seems stupid). It does seem strange that there wouldn't be limits or failsafes since they have to assume that any given pressure sensor is going to malfunction sooner or later. But it might also be the case that the pressure sensor had nothing to do with the disaster and it's just one thing investigators are looking at among a whole slew of things.
It's an AP story...also carried here https://www.ksl.com/article/46391781/official-pressure-sensors-focus-of-gas-explosions-probe but it is not comprehensive at all.
 

Thread Starter

Raymond Genovese

Joined Mar 5, 2016
1,658
That is actually a fascinating read. It seems like at one point, because of the lowest common denominator pipe MAOP the valves should have been set at 375.

The monitor valves were set to prevent outgoing pressure from exceeding 386 psig.


For instance, Line 132’s MAOP was 400 psig, but since Line 132 was also connected to Line 109 (whose MAOP was 375 psig), Line 132’s MOP was limited to 375 psig.

Although there is a veritable perfect storm of issues that were uncovered.

Ya know, I am not always a big fan of regulation, but reading through that report is actually pretty unsettling...and then there is the seemingly flawed practice artfully phrased...

When the director of the California Public Utilities Commission (CPUC) consumer protection and safety division discovered this practice, he stated,“artificially raising the pressure in a pipe that has identified integrity seam issues seems to be a wrong-headed approach to safety.”

*Sheesh*
 

Glenn Holland

Joined Dec 26, 2014
705
I used to work in the elevator business and I can testify that the most fail safe circuits can be defeated if someone is stupid enough to find a way to do so.

Case in point: an elevator mechanic somehow jumpered out both the hoistway door interlocks and also the car door interlock. That allowed the elevator to take off on a normal floor to floor run at 600 feet per minute ................. all while a rider was walking through the doors at the lobby. The rider was literally cut in two at the hip while the other riders gasped in horror and the elevator was turned into a bloody mess.

The elevator industry has a very strict policy on the use of jumpers (those familiar lengths of wire with alligator clips on each end), but nevertheless, near miss accidents have still occurred. Someone invented an jumper that has a timer that opens the circuit after several seconds so safety circuits cannot be permanently defeated.

Then there was the infamous Chernobyl nuclear power plant explosion that was caused by gross human error. If someone wants to do something stupid, they can.
 
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