SiteThe insurer's engineer surveyor is in reception at 8am for the annual visit. They ask for the written scheme for the compressor house. Someone finds it in the H&S cabinet.
It's dated 2014. It lists one receiver. There are two now. The second went in after the old compressor died three winters ago, along with a new dryer and a run of pipework your shift fitter put in over a weekend. None of it is in the scheme.
Most sites have a written scheme. The trouble starts when the plant changes after a breakdown and nobody tells the scheme.
Does it apply to you?
The Pressure Systems Safety Regulations cover systems with a "relevant fluid" in them. HSE sums that up as compressed or liquefied gas, including air, above 0.5 bar*, pressurised hot water above 110 °C*, steam and a few others (HSE, PSSR). The aim is to stop people getting hurt by stored energy when something fails.
On a factory or warehouse site that usually means the compressed air system, any steam boiler, some autoclaves and some refrigeration plant. HSE's leaflet adds gas-loaded hydraulic accumulators to the list of systems likely to need a scheme (INDG178).
Plain hydraulics don't count. HSE says relevant fluids "do not include hydraulic oils" (HSE, PSSR). That doesn't make the hydraulics safe. It means PUWER covers them instead, as our post on PUWER inspections explains.
What the scheme has to do
Regulation 8 is short. You can't run the system, or let anyone else run it, without a written scheme for periodic examination by a competent person. It must cover all protective devices, every pressure vessel, and the parts of the pipework where "a defect may give rise to danger" (regulation 8).
The scheme must be drawn up, or certified as suitable, by a competent person. It must say what kind of examination, how often, and any special steps to make the system safe to examine. Where it fits, it covers an exam before first use. And you must have it reviewed at appropriate intervals, then change it if the competent person says so.
HSE's leaflet on written schemes lists what a typical one contains. It includes "the maximum interval between examinations". It also names the critical parts that, if repaired or modified, should be examined before the system is used again (INDG178).
That last item is the one to read before a breakdown, not after.
Whose job is the scope?
Yours. The same leaflet says the legal responsibility for defining the scope "rests with users or owners" (INDG178). You can take advice, and many sites lean on their insurer's engineer. But deciding which kit is in the system and which parts go in the scheme is your duty.
HSE's rule of thumb is one system, one scheme. Two separate compressed air systems will probably need two schemes.
Who can be the competent person?
The regulations define the competent person as a competent individual "(other than an employee)" or a competent body (regulation 2). So it's normally an inspection body, a self-employed specialist, or your company's own inspection department.
If it's in-house, HSE wants it to be independent "from the operating functions" with enough authority to stop the kit being used (HSE, PSSR). The code of practice adds that a person able to handle a simple system may not have the know-how for a complex one (L122, paragraph 31).
How often?
There's no fixed interval in the regulations. The competent person sets it, using their judgement. The code of practice gives the old intervals as a guide. Steam plant was usually examined every 14 months*. Air receivers on compressed air systems were generally every 24 to 48 months*, and could stretch to 72 months* where corrosion was minimal and standards were high (L122, paragraph 115).
If your scheme says something very different, ask the competent person why.
Read the report
After each exam, the competent person writes a report. It must reach you within 28 days* of the exam, or before any repair deadline in it, whichever is sooner (regulation 9). It must state which parts were examined and their condition. It sets out any repairs needed and the date they must be done by, and the date after which the system can't run without another exam.
Those dates are hard stops. You must not run the system after a repair date unless the repair is done, or after the next exam date unless the exam is done. A postponement is allowed only once per exam. It must be agreed in writing with the competent person and notified to the enforcing authority before the date.
If the competent person finds imminent danger, they must give you a written report straight away. You must not run the affected part until it's put right. They also send it to the enforcing authority within 14 days* (regulation 10).
The breakdown that breaks the scheme
This is where maintenance teams get caught. It's 3am, a safety valve is lifting and the air main is dropping. The fitter swaps the valve from stores, or cuts in a new section of pipe. The line's back by four.
Regulation 13 puts the duty on the repairer's employer. Nothing about the repair may give rise to danger or impair "the operation of any protective device" (regulation 13). HSE also warns that after a major repair or modification you "may need to have the whole system re-examined" before it goes back into use (HSE, pressure systems).
So the spare valve needs the right set pressure and the right capacity. The new pipe needs the right rating. And if that part is on the scheme's list of critical parts, the competent person needs to see it before you rely on it. A safety valve that lifts again and again is a warning, too. HSE says it may mean the system is over-pressurising or the valve isn't working (INDG261). Our compressor fault-finding guide covers where to look.
On a night like that, you want an engineer on shift who knows pressure plant. A fitter who has never set a relief valve shouldn't be guessing at one, and the scheme should say which repairs need the competent person.
It isn't maintenance
HSE compares the statutory exam to an MOT: "It is not a substitute for regular and routine maintenance" (INDG261). You still have to keep the system "properly maintained in good repair" (regulation 12). Our post on air receivers covers the day-to-day checks for compressed air. For steam, see boiler and steam failures.
What to do on Monday
- Walk the compressor house and boiler house with the scheme in your hand. Mark anything on the floor that isn't on the paper.
- Send that list to your competent person and ask for the scheme to be reviewed.
- Find the list of critical parts in each scheme and pin it up where the fitters keep the spares.
- Pull the last exam report and check every repair date has been met.
* The 0.5 bar and 110 °C thresholds, the historic examination intervals, and the 28-day and 14-day report deadlines correct as of 23 September 2026. Check the Pressure Systems Safety Regulations on legislation.gov.uk and HSE's PSSR page for the latest. Paragraph numbers refer to L122, second edition (2014).