If you read the guidance at http://www.hse.gov.uk/pUbns/priced/l101.pdf

If the criteria apply, then you have a confined space.

From the information you have given, you appear to have a confined space under fault conditions i.e. ammonia leak.

Therefore follow the HSE guidance.

You appear to have some controls in place - gas detection and monitoring. Probably others that you don't realise, such as continnous piping (welded) incorporated at the design stage - less chance of leaks, than from flanged connections etc.

I agree with Ian.
Your plant room is already a confined space.
You now need to risk assess and decide if the controls in place are suitable & sufficent.

If they are entering the plant room to take reading why can’t this been done remotely thereby eliminating the risks. I have worked in places where there was a control room that received amongst other things all instrument and plant readings and alarms.

I believe it is not classed as a confine space providing there are strong controls in place, some of which have been mentioned, that reduces the risks to an acceptable level for the task posted. There must be no reasonably foreseeable specified risk.

Having a well maintained and inspected gas room sealed boiler in a room does not make that room a confined space even throw there is a carbon dioxide hazard.

However you cannot rely solely on the fact it met the criteria through design when new. Since 2009 a lot of things could have changed making it a confined space. It may have been modified, seal may have degraded, and poor maintenance for example could result in a reasonably foreseeable specified risk. You need to regularly update your risk assessment, inspect/check, review your controls etc.
If a leek has been identified as likely this would make the plant room a confined space. It not, how to deal with a leek needs to be set out in your emergency procedures for a leek, particularly how to stop the flow.

However it may for ease of management purposes easier just to class it as a confined space.

To my mind you have a series of controls that make entering the room safe. If the alarm goes off, or whatever, then entry should not take place except under an EOP of some kind. The likelyhood of something going wrong when a person is in the room then becomes a problem to consider. How many minutes per day is the room occupied?

Just my thoughts,

jim

Thanks again for the comments, I am learning new things every day.

My thoughts follow Alfasev's otherwise we would end up having hundreds of confined spaces.
For this instance, the room is occupied for a few minutes each day by one or two persons, it has not been modified and is maintained, tested and inspected, I am not just relying on safe at time of design.
So it come back to 'without a reasonably foreseeable specified risk', which can be subjective but I believe the risk is low due to the controls, therefor there isn't a risk of change of atmosphere, therefor not a confined space.

I fully accept that there is always 'some slight risk' if 'x' and 'y' were to happen and if 'z' did 'a', but just because a pipe could leak ammonia into the room, shouldn't make it a confined space. If I use troopers C/S requirements, because there is easy entry/exit, (x2 doors in a clean and tidy 10'x10') then it isn't a C/S.
looking at the guidance, I read that (and as Ian said), it would become a confined space under fault conditions, so by virtue, not a C/S under normal conditions?

I know its easier to just say, yes, its a confined space, but I just need my brain to accept exactly WHY its a confined space.

if you look in the Dutch Purple (PGS 3) CPR 18E book the frequency of leaks from pipelines can be estimated for pipes upto 75mm dia the leak frequency is in th eorder of 5x10^-6 per metre length per year.

The most likely cause for a loss of containment will be during maintenance activities - some maintenance engineer 'fiddles' with something he shouldn't .... fails to shut down and/or isolate the system he is working on.

I would agree the controls seem to be in place - you just need to justify why no further action is required. Save having good maintenance procedures/isolation procedures and an emergency plan to cover potential leaks of ammonia.