Is the diathermic oil a relevant fluid as defined in Reg 2 (pg 11 of the ACoP).  Such oils have very low vapour pressures.  What is the max operating temp and therefore the vapour pressure ?

ie "relevant fluid" means—

(a) steam;

(b) any fluid or mixture of fluids which is at a pressure greater than 0.5 bar above atmospheric pressure, and which fluid or mixture of fluids is—

(i) a gas, or

(ii) a liquid which would have a vapour pressure greater than 0.5 bar above atmospheric pressure when in equilibrium with its vapour at either the actual temperature of the liquid or 17.5 degrees Celsius; or

The plot thickens slightly.......

The system doesn't have vessel as such, in which the state of a fluid is changed. The system goes into heat exchangers and returns through the same loop. It would be operating at a maximum of 300C.

So is Figure 1 of L122 to be read that its only a pressure vessel that should contain steam or to have a pressure x volume product >250 bar litres (presumably)? As opposed to a "system" having that pressure x volume product? Strictly speaking, it reads just "pressure vessel" to me and so should be pretty clear? Or am I missing something?

If this is the case, then Regs 8-10 don't apply, but Reg 15 will, which is taken care of in the system design.

Comments gratefully received.

Hi All,

Thank you very much for the advice and thoughts; I'll get the TDS for the oil in question and we'll work it out to confirm.

The oil will only come under DSEAR if classified as 'dangerous' i.e. flammable/highly flammable etc.

Under CLP that means a flashpoint of 60deg C or less

Hi guys,

The site is subject to DSEAR due to the nature of what is produced, but this area is new and is awaiting a repeat assessment to confirm the new equipment, so thanks for the heads up! I will take both points about the oil on board.

Thanks to all who have contributed!