Posted on 06/23/2021 9:03:23 PM PDT by BenLurkin
A water tank exploded in a Central Valley community, lifting 70 feet into the air, killing a man and prompting a state of emergency in the city of Lemoore this week.
The incident was captured on astonishing surveillance video.
When the 1.5 million-gallon city water tank ruptured Monday afternoon, the massive container flew into the air, then crumpled on impact, authorities said.
City officials released new footage Tuesday night that captured the moment the tank exploded, hurting a city employee and killing a contractor.
(Excerpt) Read more at ktla.com ...
No, that had to be a LOT of overpressure. I can’t see how striking an arc could trigger that, either.
Wow. I was expecting a water HEATER tank, a la Mythbusters, where overpressurization turns a heater tank into one of those water rockets from when we were kids.
Catastrophic failures of aboveground, atmospheric storage tanks can occur when flammable vapors in the tank explode and break either the shell-to-bottom or side seam. These failures have caused the tanks to rip open and, in some cases, hurled the tanks through the air. A properly designed and maintained storage tank will break along the shell- to-top seam.
Tanks that are poorly maintained, rarely inspected, or repaired without attention to design, risk catastrophic failure in the event of a vapor explosion. Either weakening of the shell- to-bottom seam through corrosion or strengthening the shell-to-roof seam relative to the shell-to-bottom seam will increase the vulnerability of the tank to failure along the shell-to-bottom seam. The practice of placing gravel and spill absorbants around the base of the tank, may increase the likelihood of bottom corrosion. Given years of this practice, the bottom of some tanks, especially older ones, may be below ground level, thereby trapping moisture along the tank bottom. This can weaken the bottom and the shell-to-bottom seam. Alternatively, changes to the roof seam such as modifications to or replacement of the roof, or attachments to the roof, could make the roof-to-shell seam stronger relative to the shell- to-bottom seam.
You can see orange flame under the canopy that popped off.
I’ll betcha that nat gas (methane >> butane but almost all methane) had seeped into that tank, perhaps for years, just sitting on top of the water. Methane is a very tiny bit soluble in water, the others, almost not at all. So, they probably shut off the input water for the repair. Water level drops, the space above the water starts to be sub-atmospheric pressure plus a little CH4 comes out of solution and then the gas reaches into an explosive zone. Boom. Pretty freakish accident IMO.
A Clearwell (Ground Storage)Tank are required to be Vented to Atmosphere and have a Screen to keep out critters (birds, coons, etc) even if the Vent were to be clogged/blocked the Tank would split a seam if filling or collapse in on it self, A split would mean that a welded seam failed and it would never explode and lift off the ground. And getting Pumped water to a high enough pressure would be almost impossible. The Line/System would not reach a high enough pressure fast enough to explode like that.
On the video there’s a Fire/Explosion on the screen. I want to know what the Fuel was ?!?!
Interesting citation. Thanks. The author postulates a lot of pathways that could create an explosive mixture in a water tank. A couple of commenters suggest these are not plausible given the concentrations of chloramine in the water.
Given these possibilities, why aren’t explosive gas concentrations monitored in water tanks?
That’s exactly what I had in mind. Thanks for the link.
I forgot about H2S !
I saw a yellow flash near the top of the tank suggesting it was a bomb blast.
Methane from the ground??
That would be my guess too. Natural gas, or more likely hydrogen sulfide. The tank was only partially full.
Hydrogen Sulfide
CAS RN: 7783-06-4
Explosive Limits / Potential
Explosive limits when mixed with air: lower limit 4.3% by vol, upper limit 46% by vol.
Moderately explosive when exposed to heat or flame.
FORMS EXPLOSIVE MIXTURES WITH AIR OVER WIDE RANGE.
Wow
My thinking/thoughts. Elevated tanks use gravity to supply water. I do not know of any that would be pressurized. Tanks have vents to allow air to escape as the tank fills. Tanks have overflow ports should pumps not shut off via the sensor placed at the desired “full” mark.
yup,whatever it was,was at the top as you can see the top bulge up before the whole tank comes off the ground
hydrogen?
was interesting but not actually very conclusive. The original poster's use of chemical equation notation gave me flashbacks to interactions with one of my subordinates who was a chemical engineer. His dad who was one of my best friends on the department and was also a chemical engineer, but his son was someone who could be very difficult to get along with and typically did not take orders well on scene.
Both methane and hydrogen sulfide are commonly found in well water so it is not necessary to come up with the formulas explaining how explosive gasses could be formed within the tank. They are both lighter than air so a slowly accumulating explosive mixture of air and gas would be found somewhere near the top of the tank.
Hydrogen sulfide has a wider flammability range from 4.5% to 46% vs methane which is 4.4% to 16.4% but it has a very strong odor and it also dissolves in water forming a weak acid and bad tasting drinking water. If the water company was having enough trouble with hydrogen sulfide that they were accumulating volumes in their tanks large enough to create an explosive hazard... they would know about it and have to be treating their water.
Methane is colorless and odorless and commonly found in well water but again it seems a little unlikely that the water company would not know about it and be treating their water if they had enough that it would be forming explosive mixtures near the tops of their tanks. But stranger things have happened.
I did find the posts mentioning hydrogen to be very interesting. Hydrogen has a broad range of flammability from 4% to 74%. It is formed when an acidy solution comes into contact with magnesium, aluminum, zinc and iron. And also when a basic solution from sodium hydroxide and other chemicals used to treat water comes into contact with aluminum or zinc. But if it were hydrogen the ignition would have to have been at the top of the tank and that is not what it sounds like happened here. The video linked to in the thread here makes no mention of what they were welding on but the Fresno Bee says the ignition happened when the four workers “went to start the tie-in”.
https://www.fresnobee.com/news/local/article252270353.html
That type of operation would take place near the bottom of the tank. I appreciated your link to the EPA paper about the reason older tanks become weaker at the bottom than the top through corrosion. I am at a loss to explain the mechanism of how this mishap occurred with the information provided.
It occurred while welding or cutting was taking place so that most likely was the triggering event, but how could that operation ignite flammable gasses at the top of the tank? It does not make much sense. There is not a flammable mixture the bottom of a tank full of gasoline.
It does not seem possible that atmospheric pressure could hurl all that steel 70 feet in the air. I could understand the tank structure going up a few feet from a catastrophic failure of the bottom of the tank but the video clearly shows that much more pressure was involved.
My best guess is that somehow air pressure was feeding back into the tank and something that was done to “tie in the tanks” either welding or cutting caused a weak spot that suddenly pricked the balloon at a weak area at the bottom of the tank. Electrical connections arcing as the structure broke loose might explain the light show that some people think that they see in the video.
Good insights. Thanks. What puzzles me is that atmospheric pressure water tanks are open to the atmosphere at top (right?). The openings are covered with a screen to keep out debris and animals. So one would think that would prevent an explosive regime from being reached, wouldn’t it? Especially because most of the resulting hydrocarbon gases are less dense than air.
It’s puzzling why a side seam didn’t fail first, but all the bolts or welds at the connection between the sidewalls and floor let go simultaneously. That is what suggested to me corrosion problems at the floor/sidewall junction.
Sorry my last post I was kind of thinking out loud. This tank was not elevated. It could be that there was enough corrosion at the base of the tank that the bottom failed while it was still at normal water distribution pressures. Cutting in the tie in that they were working on might have found a weak spot. No explosion necessary.
“A chlorine bomb is a small explosive device which uses the pressure of chemically produced chlorine gas or other chlorine-containing gases such as hydrogen chloride to produce an explosion. The reaction produces an expansive increase in pressure, eventually rupturing the container.”
Chlorine gas or other chlorine-containing gases such as hydrogen chloride.
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