Introduction to pressure equipment

A pressure system is one that contains or is likely to contain a relevant fluid over 0.5 bar.

Many types of pressure equipment can be hazardous – examples are:

  • boilers and steam heating systems
  • pressurised process plant and piping
  • compressed air systems (fixed and portable)
  • pressure cookers, autoclaves and retorts
  • heat exchangers and refrigeration plant
  • valves, steam traps and filters
  • pipework and hoses
  • pressure gauges and level indicators
  • steam coffee machine

When things go wrong, these types of equipment can cause serious injuries and even fatalities. However, assessing the risks and putting proper precautions in place will minimise the chances of any accidents occurring.

Why pressure equipment safety is important

If a piece of pressure equipment fails and bursts violently apart, the results can be devastating to people in its vicinity.

Causes of pressure-related incidents

The principal causes are:

  • poor equipment and/or system design
  • poor installation
  • poor maintenance of equipment
  • inadequate repairs or modifications
  • an unsafe system of work
  • operator error, poor training/supervision


The main hazards are:

  • impact from the blast of an explosion or release of compressed liquid or gas
  • impact from parts of equipment that fail or any flying debris
  • contact with the released liquid or gas, such as steam
  • fire resulting from the escape of flammable liquids or gases

What you have to do

Assess the risks

You need to assess the levels of risk. The level of risk from the failure of pressure systems and equipment depends on a number of factors including the:

  • pressure in the system
  • type of liquid or gas and its properties
  • suitability of the equipment and pipework that contains it
  • age and condition of the equipment
  • complexity and control of its operation
  • prevailing conditions (for example a process carried out at high temperature)
  • skills, knowledge and experience of the people who maintain, test and operate the pressure equipment and systems

Basic precautions

To reduce the risks you need to know (and act on) some basic precautions.

Ensure the system can be operated safely, for example without having to climb or struggle through gaps in pipework or structures.

Be careful when repairing or modifying a pressure system. Following a major repair and/or modification, you may need to have the whole system re-examined before allowing the system to come back into use.

Ensure there is a set of operating instructions for all of the equipment in the system and for the control of the system as a whole, including in emergencies.

There should be a maintenance programme for the system as a whole. It should take into account the system and equipment age, its uses and the environment in which it is being used.

Fit suitable protective devices and ensure they function properly - for example devices such as safety valves, bursting discs and electronic appliances, and ensure they are adjusted to their correct settings and in good working order at all times.

Know the operating conditions - including the characteristics of the relevant fluid in the system and the safe operating limits of the equipment.

Written scheme of examination

A written scheme of examination is required for most pressure systems. This should be drawn up (or certified as suitable) by a competent person – someone who has the necessary skills, knowledge and experience to carry out the work safely. It must cover all protective devices, every pressure vessel and those parts of pipelines and pipework which, if they fail, could be dangerous.

The written scheme must specify the nature and frequency of examinations and include any special measures that may be needed to prepare a system for a safe examination.

A statutory examination carried out in line with a written scheme is designed to ensure your pressure system is suitable for your intended use. It is not a substitute for regular and routine maintenance.

You can find out more about doing a written scheme of examination in the PSSR Approved Code of Practice (L122).

How you do it

First of all, consider whether the job can be done another way without using pressure equipment, for example using vacuum equipment for cleaning rather than compressed air. If you have to use pressure equipment, do not use high-pressure equipment when low-pressure will do.

Provide safe and suitable equipment - ensure the equipment is suitable for its intended purpose and installed correctly and any modifications/repairs are carried out properly.

Before using pressure equipment, ensure that you have a written scheme of examination if one is required. Also make sure that any inspections needed have been completed by a competent person, and that the results have been recorded.

Always operate the equipment within the safe operating limits. If these are not provided by the manufacturer or supplier, a competent person can advise you, for example your employers' liability insurer.

Provide instruction and appropriate training so that anybody who operates, installs, maintains, repairs, inspects or tests pressure equipment has the necessary skills and knowledge to carry out their job safely. Also include what to do in an emergency. Refresher training should be included.

Ensure you have an effective maintenance plan in place, which is carried out by appropriately trained people.

Make sure that any modifications are planned, recorded and do not lead to danger.


A company using a steam boiler in their manufacturing processes

A company used a steam boiler in its manufacturing processes. An alteration to pipework inadvertently caused salty water to be introduced into the boiler.

The resulting build-up of scale caused its furnace to overheat and collapse internally, creating an explosion. This blew out the ends of the boiler house and the ejected boiler demolished an electrical substation hundreds of feet away before coming to rest.

How the accident could have been prevented

This accident could have been prevented by giving the maintenance staff correct information and instruction, and by adequately managing the maintenance operation.

As a result of the damage to the building, its contents and exterior damage, the company had to replace the boiler and rebuild the boiler house, with significant loss of production.

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Updated: 2023-01-30