PSSR Explained: Pressure Systems and the Written Scheme

PSSR applies to systems containing a relevant fluid: steam at any pressure, gases or gas mixtures above 0.5 bar gauge, and fluids that become gases when released. In a typical commercial building that captures steam boilers and their associated pipework and vessels, compressed air receivers, and some pressurised hot water and expansion arrangements. It does not apply to systems below the pressure threshold, which is why an ordinary sealed heating circuit generally falls outside it while a steam plant does not.

The scope question is worth settling deliberately rather than by assumption, because the boundary determines whether a written scheme is legally required or merely good practice. Where a site has a compressed air installation for controls or workshop use, it is very often in scope and very often the item nobody has a scheme for.

The recurring failure is not a missed examination but a missing scheme. Sites inherit plant through acquisition, mobilisation, or a change of managing agent, and the scheme — a document that lives with the installation rather than the maintenance contract — does not come across. The examinations may still be happening because an insurer arranges them, but nobody can produce the document that defines what should be examined and how often, which means nobody can confirm the examinations are adequate.

The second failure is the operating limits. A scheme is written against specific safe operating limits, and those limits must be established and observed. Where plant has been modified — a receiver replaced, a boiler re-rated, a system re-piped — the scheme needs revisiting rather than carrying on unchanged. Modification records and the original commissioning data are what make that judgement possible, which is why they are worth keeping findable.