When Is PSSR Required? Knowing If the Rules Apply to You
- Nexus Examination
- Jun 26
- 3 min read
A lot of businesses assume PSSR is something only large industrial sites have to worry about. In practice the trigger is simpler than that, and it bites before you even switch the system on. Here is when PSSR is required, when you specifically need a written scheme, and the timing that catches people out.
When Is PSSR Required?
PSSR is required whenever a pressure system used at work contains a relevant fluid above 0.5 bar, which includes steam, compressed air and other gases. A written scheme of examination must be in place before the system is operated, and for compressed air systems that duty applies once the receiver reaches 250 bar-litres.
So the test is about the fluid and the stored energy, not the size of your business. We carry out PSSR examinations across Berkshire and the surrounding counties, and plenty of smaller workshops are surprised to find they are firmly in scope.
When the Regulations Apply
PSSR applies once a system contains a relevant fluid above 0.5 bar above atmospheric pressure. The relevant fluids are:
Steam, at any pressure
Compressed or liquefied gas, including air, above 0.5 bar
Pressurised hot water above 110°C
A gas dissolved under pressure in a solvent, such as acetylene
It is not only compressed air, either. A refrigeration system with a refrigerant receiver is caught too, because the refrigerant is a liquefied gas held under pressure. The HSE's PSSR guidance sets out the definitions in full.
When a Written Scheme of Examination Is Required
Applying the regulations and needing a formal written scheme are not quite the same thing. For compressed air and gas systems, the written scheme is required once the pressure vessel reaches 250 bar-litres, worked out by multiplying its maximum working pressure in bar by its internal volume in litres.
To put numbers on it, a 100-litre air receiver running at 10 bar is 1,000 bar-litres, well over the line. Steam systems are different: they need a written scheme whatever their size. Below 250 bar-litres a system is generally outside the formal written scheme requirement, but you must still keep it safe and maintained.
When PSSR Applies in Time
The timing matters as much as the threshold, because the duties start early and recur. A written scheme and examination are required:
Before the system is used for the first time
Before any new or second-hand system is brought into use
At each interval set out in the written scheme
After any significant modification to the system
Before returning a system to use following a major repair
In our experience this is where businesses slip up most. The scheme has to be in place and the first examination done before the system goes live, not at some point afterwards.
When PSSR Does Not Apply
Not everything under pressure is in scope. Hydraulic systems are the main exception, because hydraulic oil is not a relevant fluid and these systems do not store energy in the same way.
Vacuum systems are not covered, nor is pressure created simply by a head of liquid, and anything at or below 0.5 bar falls under the threshold. These still need to be safe and well maintained, but they do not require a written scheme under PSSR.
The Bottom Line
PSSR is required whenever a system used at work holds a relevant fluid above 0.5 bar. A written scheme is needed before the system runs, triggered for compressed air once the receiver hits 250 bar-litres, and for steam at any size.
Work from the fluid and the stored energy first, get the scheme and the first examination done before the system goes live, and re-examine on schedule and after any major change. Our thorough examination services can confirm whether your system is in scope and handle the scheme from there.
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