Need some safety tips to welding on open top sewer treatment plant

[kali]

Hi, we need to do some welding on a small open top sewer treatment plant. Should we be concerned from the gases from the human waste? It is open top and not enclosed in a building, sample image below to give a rough idea. Thanks

[bakodiver]

Buy or rent a combustable gas detector.

[Oldendum]

Open top or not, methane can collect.

Deadly methane gas emanating from a dairy farm's manure pit killed five people, including four members of a Mennonite family, authorities said. https://www.cbsnews.com/news/gas-fro...on-dairy-farm/

[thegary]

I need more info. Are they going to drain the tank. Is it an aerator where the affluent is constantly stirred and air injected ? I have worked in and welded in several. The gas explosion monitor is going to be needed and it is considered a confined space even though it has an open top. So you will need the tank tested before you go in and will need a hole watch . If it is not being drained and cleaned first you are not going to want to weld in it. When we would go in them that still had affluent in them we had to wear a gas alarm on our belt . We would wear hip boots or waders . We had to walk very slow and deliberate or we would stir up the affluent and it would give off enough gas to set off the gas alarm and we would have to get out. We would not weld at those times . We were in them to replace the SS wear troughs. Nothing was used that could produce a spark. The covered ones that look like a turtle shell we would have to wear fresh air systems to breath and gas detectors on our belts.

The one pictured is very tiny . If that has the whole process in that one tank it is the smallest one I have ever seen. Most of them I have worked on just the aerator tanks is about 10 times that size. We would have to go into a row boat to work on them and always had to wear a life vest . The aerated water would make a person drop like a rock to the bottom. There was no such thing as being able to swim it is impossible.

[kali]

This will be for the aeration portion of the tank, we need to weld some additional cross beams across the top and patch up some small areas on the top edge due to corrosion (image enclosed). We did not have plans to drain the tank but we can easily drop the level 4 feet or so. Completely emptying the tank is a lot more work as the plant is currently in use and we would have to get the waste hauled off. Some even say those gases many remain for a while after clearing out the tank, safety is #1 priority so we would do whatever it takes. We do have plans to turn off the aeration and the lift station 12 hours before any work to take place. Thanks bakodriver I ordered a few combustible meter off Amazon for $30.


Recommendations?

I need more info. Are they going to drain the tank. Is it an aerator where the affluent is constantly stirred and air injected ? I have worked in and welded in several. The gas explosion monitor is going to be needed and it is considered a confined space even though it has an open top. So you will need the tank tested before you go in and will need a hole watch . If it is not being drained and cleaned first you are not going to want to weld in it. When we would go in them that still had affluent in them we had to wear a gas alarm on our belt . We would wear hip boots or waders . We had to walk very slow and deliberate or we would stir up the affluent and it would give off enough gas to set off the gas alarm and we would have to get out. We would not weld at those times . We were in them to replace the SS wear troughs. Nothing was used that could produce a spark. The covered ones that look like a turtle shell we would have to wear fresh air systems to breath and gas detectors on our belts.

[thegary]

You need a 4 gas confined space monitor. they are a lot more than $30 . The ones we used were $1200 25 years ago. The monitor will tell the whole story. If it has a sniffer pump and a hose you run the hose down into the tank and it must be tested at the bottom , center and near the top of the tank. If it does not alarm I would say you could weld . I will say we always drained them and the inside was pressure washed or steam cleaned when we welded in them. I would suggest hiring a company that does a lot of confined space entry even if your guys do the work. The 4 gas monitors have to be calibrated each week and there is a lot of things to consider . Most large millwright/ Iron worker contractors have safty coordinators and all the confined space stuff .

[CrookedRoads]

Yep it looks like somebody's trying to do a cheap patch job on this project, are you working for a contractor because I can't imagine the plant operator trying get away with this type of work. The operator of that plant should clean out and deactivate that tank before you do any work. That way they can do a proper inspection of that system while it's down.

[kali]

There is nothing else wrong with the plant, we are just patching up a few rust spots and adding additional bracing on top. Yes we can make this into a full blown event that costs tens of thousand of dollars, but it is not necessary. Its more the owner of the plant, maintaining the plant vs the operator. In addition, patch jobs happen all the time on these plants, it is nothing new. If the cost becomes too expensive an alternative route is to build an external platform in place of the cross bracing.

Yep it looks like somebody's trying to do a cheap patch job on this project, are you working for a contractor because I can't imagine the plant operator trying get away with this type of work. The operator of that plant should clean out and deactivate that tank before you do any work. That way they can do a proper inspection of that system while it's down.

[thegary]

If you and the owner of the plant want their tails covered hire a company that does confined space all the time. There is a lot to it to be OSHA legal. First everyone must be confined space trained by a certified trainer. This all has to be documented. You have to use a confined space entry permit system. You have to have a full time hole watch. Welding in a confined space changes the confined space environment on real time, that means not only monitoring it with a 4 gas meter to enter but that meter has to be used the whole time the welding is being done. The gas monitor must be tested daily and calibrated weekly. The gas modules in the 4 gas meter have a specific life and must me replaced when they will no longer calibrate correctly. There needs to be fire permits used also. Even if they guys do not go in but just lean down into the tank it is considered entry. The guy doing the gas monitoring has to be trained by a certified trainer also.

It is possible to hire a larger contractor come in and train your guys for everything and rent you the confined space equipment you will need including the 4 gas monitor. To own the meter is just the beginning. To have it OSHA legal when it is needed is another story. For an outfit that does not do vessal entry all the time it is not a good idea to have it and try to keep it calibrated and tested all the time.

[kali]

If you and the owner of the plant want their tails covered hire a company that does confined space all the time. There is a lot to it to be OSHA legal. First everyone must be confined space trained by a certified trainer. This all has to be documented. You have to use a confined space entry permit system. You have to have a full time hole watch. Welding in a confined space changes the confined space environment on real time, that means not only monitoring it with a 4 gas meter to enter but that meter has to be used the whole time the welding is being done. The gas monitor must be tested daily and calibrated weekly. The gas modules in the 4 gas meter have a specific life and must me replaced when they will no longer calibrate correctly. There needs to be fire permits used also. Even if they guys do not go in but just lean down into the tank it is considered entry. The guy doing the gas monitoring has to be trained by a certified trainer also.

It is possible to hire a larger contractor come in and train your guys for everything and rent you the confined space equipment you will need including the 4 gas monitor. To own the meter is just the beginning. To have it OSHA legal when it is needed is another story. For an outfit that does not do vessal entry all the time it is not a good idea to have it and try to keep it calibrated and tested all the time.

Thegary thanks for the response, they wont be entering the tank or even standing on top of the tank, they will be doing the patching from a scaffold and the 2 cross bracing they wanted to add sits on top.

[Munkul]

If you don't know what you should be doing regarding sewage gasses, then I would walk away, let someone else have the accident. The Owner-operator sounds like a cowboy and he's gonna get someone hurt, somewhere, somehow, down the line.

[BD1]

We did similar work replacing guard rails.
The Jobsite company provided Hot Work Permits giving us the OK for open flame and welding.
Our owner was still concerned for our safety and hired a Confined Space Contractor. This was not confined space work but gas fumes were a concern.
Our hired contractor monitored constantly and gave us the OK for cutting and welding.
This was outside work, on top of grating, installing guard rails.
I know it may sound like overkill, but better than being killed.


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[moose]

Spent 35 years working around previously rented water. The area you are working around as stated is a confined space as defined by OSHA. If you just reach a hand past the edge of the tank it is considered an entry. There are serious gases emitted by the breakdown of the waste both hazardous to breath and flammable. The team working on this needs to be both aware of and trained to deal with these. IF you do continue BE SAFE! We received training in fall arrest, rigging, confined space entry, space monitoring minimum yearly. As stated the equipment to do this safely ain't cheap BUT neither is anyones life!

[bead-boy]

Partially draining that tank will just allow more room for the gas to collect. The heavier than air gas that collects at the bottom and gets a few people a year, just by entering is Hydrogen Sulfide. And more than a third of deaths are the rescuers who rush in to pull the first victim out. I believe that the OSHA Safety Watch is required to follow strict protocols and NEVER allowed to enter the space.

Methane is lighter than air and should not be a very high concertation in an open tank like that, but could be high in boxed in areas.