How large is the confined space? And how accurate is your glow guage for the purge Nitrogen?

As an example - if you are working in a 2m x 2m x 2m 'box' (8000 litres) with continuous air flow through which is designed for a minimum of four (probably more) air changes per hour.
Then - with 8000 litres of air being pumped through the space every fifteen minutes the addition of 1 lpm of Nitrogen (15 litres in the same 15 minute interval) is neither here nor there. I think you may be being a bit too picky?

HOWEVER - if the N2 purge equipment is permanently installed - and the space is only ventilated when guys need to work in it - then you will, over time, produce an Oxygen deficient atmosphere which will require a period of ventilation when first opened up.

It may be possible to route the vent from the purged equipment outside the space - this would avoid the potantial O2 depletion risk.

Or (perhaps, and most expensively) could you replace the purged equipment with enclosed or pressurised kit that may be seen as more reliably safe in the longer term? (Doesn't rely on an external supply of purge gas)

Steve

Obviously you will carry out a risk assessment and put in place any findings. We purge our lasers with nitrogen. As they are not sealed the nitrogen then escapes to atmosphere (cleanroom). A lot will depend on the amount of nitrogen that can escape if there is a leak. If it is a as cylinder or a liquid nitrogen tank then the possible amount of gas is finite and can be calculated, however if it is from a nitrogen generator then in theory the quantity of gas will keep flowing in. We have all three types - dont ask why! We have oxygen deficiency monitors around the room that alarm on low oxygen rates. There is the BOC website which can be quite good. You could also contact suppliers of low oxygen alarms / monitors they can advise (although they will probably try and sell you their equipment). Hope some of that helps.

Thanks Maroc
Is your purging in a confined space? do you guys use a permit to work?

To add a word of caution. We have a room where the air is recirculated, and when the nitrogen line was accidentally displaced so that it was leaking into the room the oxygen level fell to 9% over a period of time. If we had not had oxygen monitoring in that room, the next person to enter it would have died.