Posted By John Webster
Firstly, check the maximum design flowrate for your oil interceptor is not exceeded. However, I doubt if a flow of 1500 gallons over 24 hours (~1 gallon/minute) is going to tax a drainage system which will be designed to cope with heavy rain. Sure you mean 1500 not 15000?

Any sludge should be suitable for disposal in a non-hazardous landfill as used for earth and builders rubble etc. Scale is essentially limestone, the sludge is compost or humus.

Suggest suitable respiratory protection for those entering the tank, as there is a slight risk from legionella if any water from the sludge is aerosolled and inhaled, and good hygiene practices, both the covering of any wounds and washing hands & exposed skin etc.

Posted By Adrian Watson
Dear All,

Whilst there is a theoritical risk from legionella, unless you are power jetting the inside, there is a very real risk that the tank is oxygen depleted if there has been any rusting inside the tank. As stated by an earlier respondant this tank entry must be dealt with as a confined space entry.

As it is a potentially OXYGEN-DEPLETED atmosphere, there must be pre-entry atmosphere testing and there must be a full entry and evacuation plan.

You should note that if the normal respirators are not suitable for entry into an oxygen depleted atmosphere.

Regards Adrian Watson

Posted By John Webster
I had not mentioned the confined space aspect as the question related to environmental impact of disposal of a small quantity of clean water and some tank sludge.

However, rusting is NOT going to result in significant oxygen depletion. The tank will start off full of the fresh air that has replaced the drained water, and if this is an open tank with removable cover (I don't know your dimensions but I am envisaging something like 6ft x 10ft x 6ft deep) then oxygen levels will stay normal. Obviously, ongoing ventilation needs to be considered if entry is through a hatch.

I would be much more concerned if there turned out to be a significant layer of sludge as this could release Methane and Hydrogen Sulphide, the first highly explosive (see Abbeystead disaster) the latter highly toxic.

Posted By Merv Newman
I must admit that I've never thought to empty and clean a sprinkler reserve tank. What with annual flow tests and weekly running of the pumps I suppose that the contents were renewed every year or so. We did send a frogman in to inspect the lining about every three years, I think. No memory of any sludge or lime scale being reported. Would you get much from potable water in a closed tank ?

Mike, when you do get the tank sorted, can you come back and tell us what it was like ?

Merv

Posted By Adrian Watson
I thought the Abbeystead disaster was due to a methane explosion?

On Wednesday 23 May 1984, a group of 44 people was assembled in a valve house set into a hillside at the outfall end of the Lune/Wyre Transfer Scheme at Abbeystead. The visitors were attending a presentation to allay anxieties on the effects of the installation on the winter flooding of the lower Wyre Valley.

As part of this presentation, water was to be pumped over the weir regulating the flow of water into the Wyre. Shortly after pumping commenced there was an intense flash, followed immediately by an explosion causing severe damage to the valve house.

Sixteen people were killed; no one escaped without injury from the valve house.

The explosion was caused by the ignition of a mixture of methane and air, which had accumulated in the valve house. The methane had been displaced from a void, which had formed in the end of the Wyresdale Tunnel during a period of 17 days before the explosion when no water was pumped through the system.

No source of ignition for the explosion has been positively identified. Thorough examination and testing of the electrical equipment has not revealed any faults likely to have caused ignition and there is insufficient evidence to confirm any of the other explanations which have been considered. Smoking in the Valve House was not prohibited because the likelihood of a flammable atmosphere arising there had not been envisaged.

Posted By ivorfire
I have e mailed you direct. Hope this helps!
Shaun