The Pressure Systems Safety Regulations 2000 (PSSR) require all users or owners of
pressure systems to demonstrate that their equipment is safe for use in order to prevent serious injury that could occur due to failing systems. In order to do this for all pressure systems containing a relevant fluid, with a few exceptions, (pp 51-56) a Written Scheme of Examination (WSE) must be in place and an inspection must be undertaken.

What is a Relevant Fluid?


  • A gas at a pressure higher than 0.5 bar
  • Steam at any pressure
  • A liquid which would have a vapour pressure greater than 0.5 bar above atmospheric pressure when in equilibrium with its vapour at either the actual temperature of the liquid or 17.5 degrees Celsius
  • A gas dissolved under pressure in a solvent contained in a porous substance at ambient temperature and which could be released from the solvent without the application of heat.

What is a Pressure System?


  • A system comprising one or more pressure vessels of rigid construction, any associated
    pipework and protective devices
  • The pipework with its protective devices to which a transportable pressure receptacle is, or is intended to be, connected
  • A pipeline and its protective devices (pipeline is a pipework crossing boundaries of

However, PSSR applies to only those Pressure Systems which contain relevant fluid.
The user for installed and the owner for mobile systems have a legal responsibility for defining the scope of the WSE and they may need to seek out advice through other means, such as a Competent Person or independent consultants.

Mobile systems are those which are moved from location to location. However, skid-mounted boilers for hire, locomotives and storage tanks moved from site-to-site are considered as installed systems and are the responsibility of their users.

What is a WSE?

A WSE is a legal document to be prepared by a Competent Person or by an individual with
required technical expertise and certified by a Competent Person.

What is a Competent Person in terms of PSSR?

A Competent Person is a company or a self-employed person with attributes given in Approved Code of Practice (ACOP) to PSSR 2000. This can be found in the Health & Safety Executive (HSE) publication L122, which can be viewed here.

A Competent Person will either be appointed to help create the WSE, or review an existing one previously created by another Competent Person. In terms of PSSR 2000, being ‘competent’ isn’t only measured by the amount of experience someone has with the equipment or time spent within a company.

There are certain measures you can take to ensure that the person you assign meets all
requirements set by HSE in ACOP to PSSR 2000. These are:

  • Qualification: Incorporated or Chartered Engineer depending upon the complexity of the equipment
  • Experience and knowledge: of the law, codes of practice, examination and inspection
    techniques, with an understanding of the effects of operation for the system concerned
  • Resources: established access to basic design and plant operation advice, materials
    engineering and non-destructive testing (NDT) facilities
  • Organisation: effective organisation, facilitating a Competent Person to address all
    PSSR related matters in accordance with the complexity of the system.

According to HSE guidelines, the ‘Competent Person’ must have appropriate industry
knowledge and the ability to be independent and impartial throughout drafting the WSE and the examination itself. This is to ensure that there is no conflict of interest between the Competent Person/inspecting body and owner/user, thus preventing unreliable results that could be unsafe in terms of equipment being tested incorrectly.

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What’s included in a WSE?

  1. A description of each part of the pressure system, subject to examinations under PSSR, including:

    1. Pressure vessels
    2. All associated protective devices
  2. All pipeline and pipework in which a failure can cause serious injury. An identification of the system e.g.: identification numbers
  3. The type and nature of the examination required, including the testing, to be carried out on any protective devices
  4. The necessary work needed to allow the system(s) to be examined safely, such as:

    1. Cooling down periods
    2. Isolation procedures
  5. The time allowed between examinations
  6. Parts of the system which, if changed or repaired, should be re-examined before the system is used again
  7. The name of the Competent Person verifying the WSE
  8. The date of the certificate

When do I need a WSE?

PSSR regulation 8 places a duty on the user of an installed system and the owner of a mobile system not to allow a pressure systems/equipment to be used until they have a WSE in place.

As PSSR applies only if a pressure system contains a relevant fluid, you need to have a WSE in place only when the system contains a relevant fluid.

Below is a few examples of vessels, associated pipework and protective devices constituting a pressure systems that require inspections in accordance with WSEs under PSSR:

  • Compressed air receivers, steam sterilising autoclaves
  • Steam boilers
  • Process vessels
  • Storage tanks and other vessels containing any type of gas
  • Pipelines crossing the boundaries of a site
  • Pipework to which a transportable pressure receptacle is connected or intended to be
  • Vessels containing pressurised hot water at temperatures which can flash to steam at lower pressures.

A Common Exception - A WSE is not required for a pressure system containing a relevant fluid (other than steam) if the product of the pressure (in bar) and internal volume (in litres) of its pressure vessels is less than 250 bar litres.


How often is a WSE needed?

A WSE will need to be reviewed and, if necessary, amended and certified by a Competent
Person whenever there is a repair or modification to the system. Moreover, a regular periodical review, by a Competent Person is also required every 3 to 5 years, depending on the complexity and the potential of a failure of any component of the system.

How to Choose a Competent Person

It can be difficult for companies to choose a Competent Person. This is because, sometimes, it’s unclear who would be the best person for the job, whether it be an in-house engineer, or an external consultant.
For Engineering Managers, the whole process of drafting a WSE, or finding someone to help them, is often made unnecessarily complex which can be frustrating when you already have a large workload.

To find out more information on WSEs and how best to ensure your pressure systems are
compliant with PSSR, please download: The No-Nonsense Guide to Your Engineering Inspections.

The guide contains all the information you need to gain a better understanding of the PSSR regulations, to an in-depth detailing of what inspections you need to have and how to go about completing them, helping you choose a competent inspection service provider and improving health and safety in your workplace.


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