Water tank explosion....yes, a water tank 4

[fel3]

https://www.yourcentralvalley.com/n...tures-deadly-water-tank-explosion-in-lemoore/

This happened in my area. I am very familiar with Lemoore and its water system because twice I was at firms that served as the contract City Engineer and I have designed some elements of that water system. My first stint was long before the Well 7 site was developed. My second stint was after the well and first tank at this site had been constructed. I helped the engineer who designed the water treatment vessels and second storage tank at this site sort out some piping connections, but I can't tell you if it was the older or newer tank that just blew up and my records are in storage.

Apparently, someone was welding something to the outside of the tank and it sparked flammable gas inside the tank (that's what the City's Public Works director speculated about in an on-site interview I saw online). This tank appears to have had a good amount of water in it, so I'm having trouble understanding how a flammable gas got into the headspace of the tank. More details will certainly come in the next days/weeks/months.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bimr]

Water quality report states hydrogen sulfide present.

 

[bimr]

Link


Hazards of hydrogen sulfide:

 

[itsmoked]

I didn't realize H2S was flammable! I knew it was more poisonous than Hydrogen Cyanide and corrodes copper quickly. I see wells frequently that provide water with HCN flavoring included. I'll be warning people in the future. A combustionable gas, meter might be a good idea.


fel3; I can see installing a new vent in the top of a tank already filled with methane as quite a challenge.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[fel3]

bimr...

That document is an excerpt from the City's current General Plan. It's the first document I've seen so far that mentions hydrogen sulfide in Lemoore's groundwater, but unfortunately it's not at all specific. I downloaded a couple recent Water Quality Consumer Confidence Reports and they didn't even mention hydrogen sulfide, nor do they break anything down by well. That being said, it seems that hydrogen sulfide is the likely culprit.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[waross]

I took an H2S safety course.
I was told that the combustible percentage for H2S was several times the lethal percentage.
I waited for the instructor to tell us that if we suspected burning H2S, it may not be a good idea to extinguish the flame.
That was never mentioned, but the company could say that all employees had H2S training.
No checks on the quality of the training.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

Having been to a firefighting school, One lesson they taught us is that it is never recommended to extinguish a fire without first securing the fuel source. Explosion becomes an issue otherwise. We got to practice on live gas fires. The water spray was used to direct the flames, not to extinguish them.

 

[itsmoked]

Excellent points Bill and Tug.

Local University of California campus had a NatG line leak. The welder threw a flare in the crater and when it didn't ignite the screaming column of gas he scrambled into the crater and welded the leak close while the leak was blasting away. I can see that as a way to prevent explosions.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TugboatEng]

I have to be skeptical about this story. If below the LEL, there is a point between that jet of gas and the surrounding air that exceeds the LEL and is ignitable.

If above the UEL, as the leak is closed the gas concentration will drop below the UEL and ignite.

Welding on anything pressurized, even inches of water, is quite challenging in the best of conditions.

I have to file this story along side the invisible steam and a broom handle myth.

 

[dik]

UEL and LEL?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[waross]

Upper Explosive Limit
Lower Explosive Limit

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[FacEngrPE]

more propriety information

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

Frequently is the natural result of decomposing anything with a sulfur content.
PEL = 20 ppm
IDHL = 100 ppm
If you observe the PEL you are far enough away from the limits of flammability.
Personnel Safety monitors are a wise investment when working around tanks (lots of other confined space situations also),

 

[RedSnake]

Here is some quite interesting facts about hydrogen sulfide, rost and water.

https://www.youtube.com/watch?v=21AM4O-p1dI

Best regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[TugboatEng]

The key when welding on a confined space is always ventilation. With adequate ventilation it doesn't matter what WAS in the space. The gas analyzer is redundant at that point.

 

[dik]

thanks, Bill


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[fel3]

I just read, on a YouTube video about the event, a comment from a guy who says he is working with the same contractor on another project in another area and the contractor told him it appears to have been a build-up of hydrogen sulfide in the tank. Of course, this is a third-hand anecdotal statement, but it also agrees with my engineer friend's speculation that it was probably hydrogen sulfide. We shall see.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[FacEngrPE]

The key when welding on a confined space is always ventilation.

The gas analyzer is needed to ensure the ventilation has run long enough to clear the space. Of course use of the analyzer requires access to the space, which is also needed to set up the ventilation.

If the welding is being performed on the outside of the tank, there is a temptation to take shortcuts with the inside of the tank, when no one is entering.

 

[TugboatEng]

Just to be clear I said the gas analyzer is redundant, not superfluous. It backs up your ventilation plan. Also, once ventilated, it's important to spot check the space for stagnant areas that may still contain unwanted gasses

 

[waross]

The primary purpose of the gas is to protect the life of the worker installing the ventilation.
Even with a Scott Pack, you want to know the presence and concentrations of lethal gas.
The gas analyzer is redundant only in the mind of a penny pinching MBA safe in an office and with no field experience.
It is probably required by law.
As far as I know it is a legal requirement here.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Eufalconimorph]

There are two uses of the word "redundant" here causing confusion.

One is the idea of a "redundant system", aka a backup. It's required for safe operation due to a possibility of failure in the primary system. For example when rock climbing we use multiple redundant attachment points to the rock so that if one fails the climber won't fall to the ground. Or for data centers there are always redundant power supplies so that when one fails the equipment keeps working. Etc.

The second is a use of "redundant" as "superfluous", IE an unnecessary extra copy of something that never gets used.

The gas analyzer is only redundant in the first sense. It's needed in the event that the ventilation hasn't completed successfully, so it's not superfluous, but ideally it'd never indicate dangerous gas levels since the ventilation would be good.

 

[waross]

Where I work, any place where gas may be present, a gas test must be completed before a safe work permit is issued.
I don't see redundant applying there.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!