Tightness test, allowable pressure drop

[Dinny991]

I've wondered for years why there is an allowable pressure drop when doing a tightness test? I get that small changes to temperature might affect the reading, but once stable after a couple of minutes and (eg) no-one is touching any pipe, why would a drop be allowed? I'm sure there is a reason why this is allowed (I'd love to be educated by wiser folk), but might the implication be that the appliance is leaking gas very, very slowly which might not be enough to smell or be identified from a leak detector?

 

[jj4091]

Not a gas man but I always presumed it was because such a small leakage would disipate quickly and not be a danger. Not sure if that would still apply to new airtight houses.

 

[gas112]

it might not be one tiny leak but several and as has been said the allowable drop is well within the safety margins and will never be dangerous .
but regardless of how small a proper leak detector placed in the right position will find it but the chances of getting the right position are very remote due to most installations not being completely on the surface

 

[Stuckinarut]

If you were a gas person you’d know. Permissible drops are only allowed if appliances are connected and no smell of gas.