Another sad example of poor hot work practices. Seeing a 1.5 million gallon tank separate its base weld and break its roof supports and head for space really should get the point across about how much potential you can be dealing with. Too many contractors and cites have no concept of sound hot work practices or combustible gas detection equipment either. https://www.wwdmag.com/tanks/deadly-water-tank-explosion-lemoore-california-prompts-state-emergency
Damn! A MSR gas detector is less than a $1,000..
Wowza! My dad tells a story about a big above ground fuel tank that he was welding inside of. The guy that was supposed to test it to make sure it was safe showed up and went inside with no detector and said "it's fine to weld, I am going to lunch, see you later!" Dad figured no way unless the guy was standing next to him when he struck the first arc. After lunch the guy checked it properly and it was fine.
Water Tank, what would or could have been inside to produce a explosion? Hydrogen Sulfide does not generally explode especially if surrounded with more water.
Because I worked on petroleum tankers some years back I went through training on confined spaces work. I still carry a confined spaces card. I can't count how many times I've seen work being done on a fuel tanker with no ground man or no one at the hatch. No vapor recovery hooked up nothing grounded plus wearing clothes that can cause static charge. Surprised they come out alive.
i'm with @DMiller , what did the introduce to that potable water tank to blow up? there sure won't be anything there under normal circumstances. I will walk that back a bit, i have seen water wells with natural gas in them. I went to school with a family that lived by the Roza dam on the Yakima River. @Truck Shop , it is that lone house down by the dam, I think the name was Riste. They would draw a glass of water and wait for it to bubble out. Many years later they drilled a test well down there, but nothing came of it.
My first thought when someone told me about it was some sort of natural/sour gas in the well water building up in the air space above the water line. Especially if the tank vent wasn't up to par.
That well was drilled by Shell, it's 15,000 feet deep. Gas was found and Shell capped the well same with the other three wells. Huge pockets of natural gas were found at each well site. They drilled on Whiskey Dick Mt and Boilston also.
Years ago, I switched propane providers. The previous company had been charging me $6.25 a gallon, and most of that was tank rental. The new company sold me a lifetime tank, and agreed to charge $2.25 a gallon. When they arrived to put in the tank, they indicated that they needed $50 to file for a fire permit to inspect the install. When I questioned why they needed an inspection when they were doing no alterations to the piping - just dropping in a brand new tank, they told me that propane could be dangerous, and that state law required an inspection. I paid the fee. One month goes by. Two months go by. Three. No word from the fire department. Since I watched the guy install the tank, and check all of the connections with soapy water, I didn't worry about it. A year later, I get a phone call from the fire department. "We need to book an appt to inspect the new install." After 10 seconds of silence, I responded, "What? Really? Why would you bother??" In his official voice, he came back with "Propane is dangerous. We need to make sure that the install was done right so you don't blow yourself up." I retorted, "So if you don't inspect, I'm in danger?" "Yep. Every single day." "Then why has it taken a year to do the inspection? The tank went in a year ago?" Silence. "Well we have to do the inspection." I agree, and we book an appt.. The guy comes out, walks around the corner of the house, looks at the tank from 20 feet away, pronounces it safe, and heads down the driveway. Lesson learned is that we are all responsible for our safety, and that we alone need to stand up when we see something that isn't right. No matter how much pressure we get from bosses, so-called experts, and anyone else, we need to stand firm on what we know is right, and not budge.
It's going to much easier to inspect the vent now that it's at ground level.
We had a family a number of years ago about 10 miles from here that had fowl smelling water. It came on all of a sudden from a farm well that was at least 50 years old. The TV news showed a match lighting it up. It would flame briefly before going out. The experts determined it to be swamp gas collecting in the well and flowing with the water. it was eventually filled with bentonite. They said it happens occasionally when the casing has a crack near the surface.