My questions would be: If the filtered compressed air was being fed to both the respiratory equipment and machinery where could the contamination occur? How would any external contamination gain entry to the system? Of course, without more detailed knowledge of the design of the system it is difficult to answer this question from here. 

Steve - does this mean that you have a completely separate air compressor system for the breathing air?

Where exactly are the filters?  On our filtered air, we have one airline from the compressor which splits and downsizes as it goes through the factory, one arm goes to a set of yellow filters above the paint booth and the airline that exits these filters goes to the breathing apparatus, but the airline continues past this point to other parts of the factory. 

Even if this were not the case, given that the compressed air is probably at 30psi as an absolute minimum, how is the contamination going to get back up the airline from the machinery to affect the breathing apparatus?

If you carry out the checks on the quality of the breathing air specified in appendix 3 of HSG to which Stevedm referred, then this should determine if there are any contaminants in the breathing air supply. (and that the filtering system is doing what it should and filters changed at the appropriate intervals etc etc).

http://www.hse.gov.uk/pUbns/priced/hsg53.pdf

If the filtered air also goes to other equipment, while unlikely, could there be a risk of some back flow when the compressors are turned off at the weekend? or if there is a ring main? - just a thought

Yes, we have a dryer and separator at the compressor and then filters at the breathing air point.

Originally Posted by: CptBeaky

Originally Posted by: hilary

Yes, we have a dryer and separator at the compressor and then filters at the breathing air point.

This is the same as our set up (for a spray room). This is why I am confused as to what the contamination issue is. If, for example, we used the filtered point for a machine then plugged the breathing airline back in, would there be a contamination issue?

I don't know how contamination could occur either.

If you are concerned about using breathing air for tools (cost of treatment filtration ) would it not be possible with a little re-plumbing to split the air immediately after the compressor and before the air dryer/filters? That way the filtered air would only be used for breathing apparatus and the filters would process less air and last longer? Or have I got the wrong end of the stick?

Kate, maybe you are right and I got the wrong end. I suppose this is one for a compressed air expert, but I thought the risk of contamination would be eliminated by the filter and dryer being on the 'breathing air' side of a backflow check valve. To me, it is possible that contamination could feasibly occur if the compressor was turned off and a pressurised line was allowed to backflow unchecked. I wouldn't have thought using breathing air from an undedicated breathing-quality airline was a good idea.

Sorry for the late reply...I have had a look at two installations just to make sure we were running on the same lines..(excuse the pun)...so yes single compressor yes single line coming out of compressor...which is then diverted..one for breathing air one for instrument air.(we still have a independant line - but that is just us apparently!)..they have 2 'surgical grade' filters (Once I have the link to the spec I will post it) on the breathing air line, with the appropriate NRVs...which gives us the purity required to comply with the breathing air standard...so although EIGA references are good and other nations do mandate independant supply (US) we don't seem to do that in the UK..I am happy, having reviewed two customer systems against our own, that the setup is ok and complies...you might want to get further advice from you vendor on the maintainance and the type of filters...but generally single line diverted looks to be ok