The Pressure Systems Safety Regulations 2000 (SI 2000/128) set the legal framework for anyone who owns, installs or operates plant that holds compressed air, steam or other pressurised gas above a stated level. They apply in Great Britain; Northern Ireland has its own, separate regulations covering the same ground. A workshop compressor with its receiver is the plant these regulations were written for, so knowing what counts as a covered system and who carries the duties is the starting point before any question about a written scheme comes up.

What counts as a pressure system

Regulation 2(1) defines a pressure system as one or more pressure vessels, together with the pipework and protective devices fitted to them, containing a relevant fluid capable of releasing stored energy on failure. A relevant fluid includes steam at any pressure and gas, including compressed air, above 0.5 bar. In a typical workshop that means the compressor's air receiver, the pipework running from it, and the safety valve and pressure gauge fitted to protect it, taken together as one system.

Who the duties fall on

The regulations put duties on the owner of a pressure system and, separately, on the user where the system is installed for use at work. In most workshops the business running the compressor is both, but where equipment is leased or supplied under a service arrangement, the party named as user in that arrangement can hold duties even without owning the plant outright. Establishing which party is the user of a given system is the first practical question, because the duties to examine and maintain it follow that person.

A written scheme of examination is the document that says which parts of a pressure system have to be examined, what each examination has to check, and how often it has to happen. It is not a certificate of compliance and not a one-off inspection report: it is a standing programme that follows the system for as long as it stays in service, and every examination carried out on that system has to match what the scheme says.

What the scheme sets out

A properly drawn-up scheme identifies the parts of the system that need examination (the receiver itself, and any protective device such as a safety valve or pressure switch that would leave the system unsafe if it failed), the nature and extent of each examination, and the maximum interval that can pass between them. It also records the safe operating limits the system was designed for, so an examiner checking it in five years' time is working from the same figures as the person who wrote the scheme.

Who writes it

The scheme has to be drawn up or certified by a competent person — someone with the knowledge and experience to judge what a particular system needs. An installer, a distributor or the compressor's own paperwork may feed into it, but the scheme itself is the competent person's professional judgement on that specific receiver and its protective devices.

When it has to exist

The scheme has to be in place before the system is put into use. Regulation 8 of the Pressure Systems Safety Regulations 2000 (SI 2000/128, GB) requires the user of an installed system to ensure it is examined in accordance with the written scheme at the intervals specified in that scheme, which only works if the scheme already exists and states those intervals. A receiver bought and connected without one is being run outside that duty from the moment it starts holding pressure, whatever the reason for the gap.

Whether a particular receiver crosses the threshold that brings this duty into play is a question of its bar-litre product, worked through in the receiver sizing guide. What happens when the paperwork is missing or out of date is set out through real enforcement outcomes in what HSE's pressure systems cases teach a workshop owner.

A competent person is someone with the knowledge and practical experience to judge whether a pressure system is safe to keep running, as the Pressure Systems Safety Regulations 2000 require. In practice this is usually an engineer working for an inspection body, following the written scheme that sets out what has to be checked and how often. The examination itself is a distinct event from the servicing a distributor or maintenance firm carries out between times, and it produces its own written report.

What the examination looks at

An examination under the written scheme covers the parts of the system that fail in ways a visual glance would miss:

• The condition of the receiver shell, welds and fittings, checked for corrosion, cracking and wall thickness where the scheme calls for it
• The safety valve, checked to confirm it lifts at the pressure stamped on it and reseats correctly afterwards
• Pressure gauges and any other protective device named in the scheme
• Whether the system is being operated within the safe operating limits set when the scheme was drawn up

Where the competent person finds a defect serious enough to affect safe operation, the report has to say so and set a date by which it must be dealt with. Ignoring that date, or carrying on running the system past it, is where a scheme stops protecting anyone.

Below 250 bar-litres, the duties don't disappear

A receiver that stays under the 250 bar-litre threshold does not need a written scheme of examination. The user still has to maintain the system and keep it within the pressure and temperature limits the manufacturer sets, because a small receiver can fail from corrosion or overpressure just as a large one can. Where a particular receiver sits against that threshold, and what a scheme should require once it crosses it, is for a competent person to judge against the system as actually installed and used.

Working out where a receiver sits against the threshold is covered in the receiver sizing guide, and what happens when an examination or a maintenance duty gets missed is set out in what HSE's pressure systems cases teach a workshop owner.

A written scheme of examination sets out what a competent person checks and when, but that paperwork is only one part of what the regulations expect from the people running the system day to day. The user of an installed system, or the owner of a mobile one, has duties that apply whether or not an examination is due: keeping the plant within its safe operating limits, maintaining it so it does not develop the kind of fault the scheme was written to catch, and acting on what the competent person's report actually says once it arrives.

Safe operating limits

Regulation 6 of the Pressure Systems Safety Regulations 2000 (SI 2000/128, GB) requires the user or owner to ensure a system is not operated outside the safe operating limits set for it, whether that means a maximum working pressure, a minimum, or a temperature range tied to the pressure. Those limits usually come from the manufacturer's data plate and the design information supplied with the receiver, and they are what every examination under the scheme is checking against. Running a receiver above its stamped maximum pressure to get a little more out of a tool breaks this duty on its own, before any examination is even due.

Keeping the system maintained

Regulation 11 requires the system to be properly maintained and kept in good repair, so far as is reasonably practicable, to prevent danger. This duty runs independently of the examination interval fixed in the written scheme. A receiver can be months away from its next examination and still need attention now, if a relief valve is sticking, a fitting is corroding, or a weld has started to weep. The scheme tells a competent person (someone with the knowledge and experience to examine the system safely, as the regulations define the term) what to look at when they visit; maintenance is what keeps the system safe in between.

What to do with the competent person's report

An examination carried out under regulation 9 ends with a written report from the competent person. Where that report identifies a defect that gives rise, or could give rise, to imminent danger, the competent person has to notify the user or owner without delay, and the affected system, or the part of it concerned, has to be taken out of use until the defect is put right. Where the report instead sets a date by which a repair or a further examination must take place, that date is a duty to meet, not a recommendation to weigh up when time allows. A report filed away unread does not satisfy the regulations, whatever the written scheme says about intervals.

Records

Regulation 13 requires the current written scheme and the last examination report to be kept available for as long as they remain relevant to the system, and to be produced to an inspector on request. A folder holding the scheme but no completed examination reports behind it does not demonstrate that the duty to examine has actually been carried out.

Whether a particular receiver, pipe run or fitting meets these duties on a given site is a judgement for the competent person who examines it. A general account of what the regulations require cannot settle that for any one system.