I will attempt to provide some relevant advice for you John.
Hoses should of course be replaced in line with the manufacturers instructions. The manufacturer is (hopefully) in control of the material specification, which in turn determines the viable life fo the hose. Medical gas hoses used in the UK are made from plasticised PVC. The plasticiser slowly migrates from the hose and makes the hose stiff; as stiff as a uPVC window frame if you leave it long enough. This phenomenon leads to hose to gradually loose its mechanical strength and resistance to abrasion. Up to 40% of the mass of the hose may be the plasticiser. Eventually hoses will fail if not replaced. It is likely this will be a good while longer than 5 years but there has to be a safety margin. I have heard anywhere from 3 to 5 years from different manufacturers. The other area you should consider are medical supply units (booms, pendants, gantry's, bweams etc.) typically in ICU/HDU and theatres. If these are adjustable they will have hoses inside feeding the gas outlets. Inspection here can be very difficult. Quarterly inspection would be quite onerous for some systems. The hoses are to some degree protected within the medical supply unit enclosure, but the rotation of say, a pendant, through as much as 340 degrees on its axis, can apply some significant rubbing and torsional stress to the hoses therein.
I recall an indcident at a hospital in the East Midlands where a hose had not been properly crimped to its fitting. This was inside a pendant in the A&E. It popped of the fitting on a Saturday night and the whole place was evacuated. Thankfully it was an air hose rather than oxygen, but the fire brigade were less than impressed.
Typically wall outlets will be 'serviced' quarterly but this typically involves only pluging in an FRDP (flow rate pressure drop test device' to prove the resistance to flow is below a defined limit i.e there is no blockage. The more likely failure will be a minor and not easily detectable leak. 1 l/min equates to over half a million litres over a year. There is a significant cost attached, especially for nitrous oxide or O2/N2O, but also a much greater risk of fire with oxygen in particular, as the local atmosphere becomes oxygen enriched.
There are better methods of PPM that can be adopted. For example targeting the high usage areas quarterly and low usage areas annually. This gives a significant drop in the total burden, since general wards are nearly always low usage but make up the majority of inpatient accomodation. If the contracted MGPS maintenance company were to take a portion, lets say half for arguments sake, of that time saving and apply it to finding and fixing leaks only, you would have a net reduction in both service budget and oxygen consumption.
BTW HTM2022 was replaced by HTM02-01 from Autumn 2006. Pretty much all the HTM's have been revised and republished in the last 3 years with a new numbering system. Quite fitting for the MGPS documents to be called 02 I think, even if it is a zero!
