Written Schemes of Examination

The Written Scheme of Examination is the document everything else under PSSR hangs off. Without it, the system cannot be lawfully examined under Regulation 9; with it out of date, examinations don't reflect how the system actually operates. This page covers what a WSE must contain, who can draft one, and the situations where we get called in to write or repair them.

Why a Written Scheme is a legal requirement under PSSR Regulation 8

PSSR Regulation 8(1) states that the user of an installed system, or the owner of a mobile system, shall not operate the system unless they have a written scheme for the periodic examination, by a competent person, of the protective devices, every pressure vessel, and those parts of the pipework whose failure could give rise to danger.

That obligation is unusual in two ways. First, the duty is on operation: the system cannot be operated without a WSE, not merely "examined." Second, the scheme must be drawn up or certified by a competent person. HSE's Approved Code of Practice (L122) allows that to be an in-house competent person who meets its criteria; where a user has the expertise to draw up a scheme but not to certify it, it says an independent competent person should carry out the certification. Our view is that an outside expert should decide what needs examining and how often, not the contractor whose commercial relationship depends on the system staying in service.

Regulation 9 then requires the system to be examined in accordance with the WSE by a competent person, with a written report retained by the duty holder. So Regulation 8 is the document and Regulation 9 is the inspection itself.

What a Written Scheme of Examination must contain

HSE L122 sets out the minimum content of a WSE. A scheme must specify:

• Every part of the pressure system the scheme covers, identified clearly enough that a different competent person could examine the same parts on a later visit.
• The nature of the examination required for each part: visual, internal, external, with or without dismantling, pressure test, ultrasonic, dye-penetrant, etc.
• The frequency of examination for each part, expressed in time intervals (months) or operating hours, with the longer period clearly distinguished from any inspection between examinations.
• The critical parts whose failure could cause danger: protective devices (relief valves, bursting discs), pressure-bearing parts (vessel walls, end caps), and any pipework whose failure could release a relevant fluid into the workplace.
• The conditions under which the examination must be carried out: vessel out of service, depressurised, opened, cleaned, etc.
• Any safeguards or temporary protective measures needed during examination work.

A well-drafted WSE is specific enough that the engineer surveyor who didn't write it can pick up the document and carry out the next examination without ambiguity. Where we inherit poorly-drafted WSEs (vague descriptions, missing parts, inappropriate intervals), we issue a revised scheme as part of the engagement.

Who can write a Written Scheme of Examination

The WSE must be drawn up, or certified as suitable, by a competent person. Under HSE's Approved Code of Practice (L122) the competent person needs practical and theoretical knowledge and actual experience of the type of system, enough to identify defects and assess their significance. L122 does not require them to be independent of routine maintenance, but where the competent person comes from the user's own organisation it expects a suitable degree of independence from the operating functions of the company. Our view is that the same person should not both service the compressor and certify the scheme that says how often it gets examined.

In practice we steer duty holders away from two common shortcuts. First, having the contractor who maintains your equipment draft your WSE: the Regulations do not forbid it, but it puts the scheme in the hands of someone with a commercial interest in how often the system is examined. Second, having the employee who runs the plant draft it: L122 accepts an in-house competent person only with a suitable degree of independence from the operating functions of the company and the expertise its criteria set out, which is rare in non-specialist organisations. The realistic path for most duty holders is to commission an external engineer surveyor.

That is the gap we fill. Our Engineer Surveyors hold the practical and theoretical knowledge HSE expects, we have no maintenance or sales relationship with any equipment manufacturer or service contractor, and we draft schemes that reflect your specific installation, not a manufacturer's generic template.

When is a Written Scheme of Examination required

A WSE is required whenever a pressure system falls within PSSR scope. PSSR applies to systems containing a relevant fluid: steam, compressed gas or vapour above 0.5 bar, or any pressurised fluid containing dissolved gas. Most workshop compressed air systems, almost all steam systems, all but the smallest commercial café and espresso machines, hospital and laboratory autoclaves, and any pressurised process equipment will need a WSE.

The clearest exemption is the 250 bar-litre threshold for installed compressors. A simple compressed air system where each receiver's capacity (litres) multiplied by its pressure (bar) is less than 250 falls outside the WSE requirement altogether (PSSR Schedule 1, Part II, paragraph 2(1)). If you operate a workshop compressor and aren't sure which side of the line you're on, send us the data plate details and we'll confirm in writing before any work is quoted.

Our WSE drafting and review service

Three common starting situations bring duty holders to us:

• New equipment, no WSE in place. A site has installed a new compressor, autoclave, or steam system and needs a WSE drafted before it can be lawfully operated. We attend, survey, draft, and supply the WSE, usually within one visit and a follow-up document.
• Inherited WSE that doesn't match the installation. A site has acquired equipment with a manufacturer's template WSE, or has modified the system over time and the WSE no longer reflects reality. We review and reissue the scheme so the next examination runs cleanly.
• HSE Improvement Notice. A site has been inspected and the WSE was either missing, drawn up by the maintenance contractor, or judged inadequate. We act quickly to draft a compliant scheme and carry out the first examination under it.

We typically combine the WSE drafting with the first thorough examination so duty holders end up with both the scheme and a current Regulation 9 report from the same visit.

WSE drafting and the periodic examination are separately quoted: the drafting is a one-off survey-and-document piece of work under Regulation 8, the examination is a recurring piece of work under Regulation 9. Our PSSR inspection cost guide walks through the WSE-vs-examination cost split in more detail and is the right starting point if you're trying to compare quotes from multiple providers.

Common pressure systems we write schemes for

• Air receivers and compressed air systems: see our air receiver service for detail on the specific examination requirements that the WSE drives.
• Café and espresso machine boilers: commercial hospitality boilers above the PSSR threshold need a WSE even though they're small.
• Autoclaves and sterilisers: hospital, dental, veterinary, and laboratory autoclaves require schemes that cover the chamber, the safety devices, and the steam supply.
• Steam boilers and hot water systems: both fire-tube and water-tube installations.
• Pressure vessels and process equipment: chemical reactors, food-grade vessels, pharmaceutical process equipment.
• Heat exchangers forming part of a wider pressure system.

Frequently Asked Questions