septic tank methane explosion

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Old 08-25-18, 09:33 AM
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septic tank methane explosion

With an electric high speed angle grinderl, I'll be cutting off around 10 5/16" bolt studs that surround a square septic tank opening, that were there to fasten down a rusted out lid. I intend on angling the grinder so the sparks are opposite direction of tank hole. Would just a box fan running, blowing over the tank hole for maybe an hour eliminate the possibility of an explosion? I won't be renting any type of handheld meter to test for presence of methane. Thx to anyone who has knowledge of this. (yeah, won't be cutting the bolts with a hand saw either)
 

Last edited by drmax; 08-25-18 at 09:50 AM.
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Old 08-25-18, 09:48 AM
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To be clear is this a septic tank or a pump tank?

If the lid will be in place when cutting I would not ventilate. The tank will have very little oxygen inside and the lid will help prevent sparks from coming in contact with flammable gases. If the lid will be off when your cutting then having the fan blow down into the tank would help. Methane is lighter than air and will rise out of the tank on it's own when the lid is removed, hydrogen sulfide is heavier than air so to remove it you'll need to force air down into the tank. The good thing is a septic tank will be 95% of poo liquid so there is very little room for gasses.

You are aware of the fire risk which is good. Also be aware that falling into the tank is probably the greater danger. If you fall in the gasses are toxic (which is bad) and the lack of oxygen can suffocate you (also bad). So, drowning with your head above water/poo is a possibility. If the hole in your tank is large you can lay a few boards across the top for safety. Having another person around when you work is also a good idea.
 
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Old 08-25-18, 10:40 AM
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ok, was informed the lid will be off. Perhaps just leaving it off and ventilate an hour before I make the sparks. No chance I'll be falling in. Not my cup of tea!
 
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