SC33 - Pressure and vacuum systems
08 Feb 2011



Safety of Pressure and vacuum systems


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1Initial releaseFeb 2010
1.1Minor addition to section 4.7Jan 2012
1.2Change to format of audit templateMay 2013
1.3Change to para 4.2.9 and addition of Appendix on document retentionSept 2014
Modification to Purpose (para 1)
Jun 2015
Added Gas Cylinder Safety Awareness Course
Jun 2015
Added generic risk assessments;
The use of warning signs; and
Drop/lift plates for vacuum systems.
Feb 2017
​Changes related to the launch of SHE Assure
​October 2018
​Minor update to training requirements in Appendix 6​
​December 2019

1. Purpose

The nature of work at the STFC involves the use of a large number of systems operating under pressure or vacuum, for example sample chambers, reaction vessels, RF waveguides, cryo-modules, heating systems, commercial coffee machine, autoclaves etc. The stored energy in pressurised systems has the potential to cause serious personal injury, significant damage to property and loss of time and money. Similarly, vacuum systems have the potential to cause personal injury through catastrophic failure (implosion).

Such failures are preventable, and the STFC aims to pro actively manage the risks associated with the design, manufacture, purchase, installation, use, modification, maintenance and repair of pressure and vacuum systems.

The Pressure Systems (Safety) Regulations 2000 (PSSR 2000) impose specific legal duties on the STFC to design, construct, install and operate safe pressurised systems, and maintain and repair them to prevent danger. Additional duties are imposed by:

  • The Health and Safety at Work etc. Act, 1974.
  • The Management of Health and Safety at Work Regulations 1999.
  • The Provision and Use of Work Equipment Regulations 1998
  • The Pressure Equipment Regulations 1999 (PER) (where STFC is supplying Pressure Systems for payment)

These regulations apply to both pressure and vacuum systems. Failures of pressurised systems which may reasonably have lead to a fatality are also reportable to the Health and Safety Executive (HSE) under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR), 1995.

2. Scope

This Code puts in place arrangements and a structure to enable the STFC to comply with its relevant duties for Pressure Systems. It incorporates all but the most basic vacuum systems to ensure that they are managed in a similar manner.

For Pressure systems that the STFC designs and builds, this code uses the Pressure Equipment Regulations (PER) 1999 as a basis for ensuring that these systems are designed and built so as to be safe when installed, used and maintained. For vacuum systems it asks that they are designed and built by a similarly consultative and documented process to ensure that they are safe to install, use and maintain.

For Pressure systems that the STFC supplies on a commercial basis within the EU then PER must be complied with in full.

The requirements of this code are mandatory across the STFC and apply to all staff, tenants, facility users, visitors and contractors working with:

  • any pressure system, including pressure systems with a Pressure * Volume of less than 250 bar litres.
  • Vacuum systems in which any component has been designed or built in-house.
  • "Off the shelf" Vacuum systems with a protective device fitted (to prevent pressurisation).

This includes: gas supply systems, steam based building heating systems, refrigeration systems with an input power of more than 25 kW (electrical) and cryogenic systems where the cryogen boil-off is able to pressurise the whole or part of the system it is connected to.

This code applies to:

  • The design, manufacture and certification of pressure and vacuum systems by STFC staff for use within STFC, and for commercial supply (by STFC) to third parties;
  • The operation, modification and maintenance of pressure and vacuum systems on STFC sites, regardless of owner;
  • The statutory examination of pressure systems on STFC sites, regardless of owner; and
  • The use of transportable pressure receptacles - for example nitrogen gas bottles - on STFC sites, regardless of owner.

This code only addresses the hazards posed by the stored energy in the system, and not any other hazard associated with it or its contents. These are covered, as appropriate by the relevant STFC SHE Codes for example COSHH and/or DSEAR.

This code does not apply to the following systems, which are specifically exempted from the PSSR regulations:

  • Where the pressure is exerted only by a head of liquid;
  • A pressure system which forms part of any braking, control or suspension system of a vehicle;
  • That part of a system which is a pressure system only because it is subject to a leak test or pressurised unintentionally or a pipeline pressurised as part of a test or line clearance;
  • Underground water and gas mains;
  • Any water cooling system on an internal combustion engine or any compressor;
  • Any tyre used or intended to be used on a vehicle;
  • Any vapour compression refrigeration system not exceeding 25 kW installed power;
  • Any portable fire extinguisher with a working pressure below 25 bar and having a mass not exceeding 23 kilograms; and
  • Any part of a hand held tool or appliance which is a pressure vessel

3. Definitions

3.1 Pressure Systems (Exempt and Non exempt)

A pressure system is one which contains or is likely to contain a relevant fluid and consists of:

  • A system comprising one or more pressure vessels of rigid construction, any associated pipework and protective devices (as may be found in a hot water heating system) or
  • The pipework with its protective devices to which a transportable pressure receptacle is, or is intended to be connected (as may be found supplying gas to a laboratory); or
  • A pipeline and it's protective devices, which contains or is liable to contain a relevant fluid, but does not include a transportable pressure receptacle.

non-exempt pressure system is one to which all the provisions of PSSR 2000 apply. An example would be a compressed air system delivering air to a number of rooms in a building.

An exempt pressure system is one to which not all of the provisions of PSSR 2000 apply because it does not contain steam and has an internal pressure volume product of less than 250 bar litres. As a result it does not require marking, does not need a Written Scheme of Examination (WSE), undergo statutory inspections or need to go through a special process for modifications. An example might be (depending on its volume) a small stand alone air compressor, used to drive pneumatic tools.

Use the flow chart in Appendix 1 to determine if your pressure system is exempt or non-exempt.

3.2 Relevant Fluid

A continuous, amorphous substance that can be considered one of the following:

  • Steam: or
  • Any fluid or mixture of fluids which is at a pressure greater than 0.5 bar above atmospheric pressure, and which fluid or mixture of fluids is:
  • A gas; or
  • 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 17.5º Celsius; or
  • 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
3.3 Vacuum System

A vacuum system is any vessel or arrangement of pipework or combination thereof, designed to work at a pressure below 500mbar absolute pressure.

3.4 Protective Devices

These are devices implemented in the system to protect it against overpressure or system failure, or devices included to give warning that an overpressure or system failure might occur. An example would be a pressure relief valve or a drop/lift plate on a large vacuum system.

3.5 Written Scheme of Examination (WSE)

This is the written scheme referred to in regulation 8 of the Pressure Systems Safety Regulations 2000.

3.6 Catastrophic System Failure

For a pressure system - the unintentional release of stored energy (other than from a pressure relief system) by explosion, tear or rupture.

For a vacuum system - the failure, by implosion, fracture or collapse of a vacuum system whilst under vacuum.

3.7 Pressure/Vacuum System Design Engineer

This is a competent engineer who designs a pressure or vacuum system for use in STFC or supply to a third party.

3.8 Pressure/Vacuum System Nominated Engineer

A departmental role - a designated competent engineer who approves the design and specification of any pressure or vacuum system designed or procured by that department. A department may have more than one such person provided the scope of their responsibilities is defined on appointment. These people are also asked to witness pressure proof tests on new systems under test on STFC sites.

3.9 Third Party Inspector

Competent inspection engineer employed by an independent accredited inspection body, contracted by STFC to carry out Statutory inspections, provide WSE's and any third party inspection or verification required under PER (witnessing of proof test, inspection of vessels during manufacture, approval of designs and specifications and assessment of manufacturers etc).

3.10 Statutory Examination

Under regulation 9 of PSSR 2000, "Statutory Examination" means examination as detailed by the WSE by a competent person independent of the equipment and its use.

4. Responsibilities

4.1 ​Directors shall:
  • 4.1.1 Ensure that the specification, design, fabrication, purchase, commissioning, operation, modification, maintenance/repair, thorough examination and decommissioning of pressure and vacuum systems are carried out by competent people and that sufficient resource and facilities are available to implement the requirements of this code.
  • 4.1.2 In consultation with other Departmental Directors appoint in writing sufficient Pressure/Vacuum System Nominated Engineers for their department, to oversee the design, fabrication and installation of pressure and vacuum systems, and witness pressure proof tests.
  • Pressure/Vacuum System Nominated Engineers, based on their competence, should be appointed in writing (template appointment letter) and their appointment and departmental scope recorded in the SHE Directory.
    Pressure/Vacuum System Nominated Engineers, based on their competence, should be appointed in writing and their appointment and departmental scope recorded.
  • 4 .1.3 In consultation with other Departmental Directors ensure that pressure and vacuum system engineers and technicians have access to a well controlled safe area to test and maintain pressure and vacuum systems.
  • For practical reasons test facilities may be shared between Departments.
  • 4.1.4 Ensure that only competent persons are authorised as "Pressure System Permit Issuers"; see Appendix 6 for training requirements. Appointment of "Pressure System Permit Issuers" should be in writing (template appointment letter) and recorded in the STFC SHE Directory.
    4.1.4 Ensure that only competent persons are authorised as "Pressure System Permit Issuers"; see Appendix 6 for training requirements. Appointment of "Pressure System Permit Issuers" should be in writing and recorded.
4.2 Line Managers shall (for all pressure and vacuum systems)
  • 4.2.1 Prior to work starting and following STFC SHE Code 6 (Risk Management) make sure that significant risks arising from the use, maintenance and repair of pressure and vacuum systems under their control have been:
    • Assessed, hazards identified;
    • Suitable control measures put in place;
    • The risk assessment recorded and assoc​iated Safe System of work developed (Generic work-area risk assessments with pressure and vacuum forming part of the overall risk assessment are acceptable).
  • And ensure that maintenance on steam systems or work involving entry into a pressure vessel is only carried out under a permit to work system, where the permit has been issued by a Pressure System Permit Issuer who is familiar with the system concerned.
  • 4.2.2 Ensure that only trained, competent personnel operate or maintain/repair pressure and vacuum systems in line with documented procedures either from the manufacturer or prepared in-house by a competent person.
  • 4.2.3 Ensure that any pressure or vacuum system brought onto STFC sites by a facility user or other person is examined by a Pressure/Vacuum System Nominated Engineer to make sure it is safe for its intended use. See Appendix 4 for further guidance on such equipment.
  • 4.2.4 Ensure that any major modifications - those that involve more than a direct swap of a component with an identical/similar one. For example: cutting into a system or welding additional material on - to a pressure or vacuum system have been discussed and approved by the appropriate Pressure/Vacuum System Nominated Engineer before they are made to the system.
  • 4.2.5 Keep a list of the systems they are responsible for.
  • Line Managers shall (for non exempt pressure systems only)(See flow chart in Appendix 1 to determine if your system is non-exempt):
  • 4.2.6 Ensure that all non-exempt pressure systems are registered with the local SHE Group, prior to first use. If a system can be both pressurised and run under vacuum (e.g. cryogenic systems) then it must be registered as a pressure system.
  • 4.2.7 Ensure that for all non-exempt pressure systems, purchased directly from a supplier or designed and manufactured by STFC "in-house", the following actions are taken:
    • Before a pressure system is used for the first time, a WSE is prepared by a competent person. WSE's can be produced in-house or by the current provider of statutory examinations of pressure systems. In house schemes should contain as a minimum the information listed in Appendix 2.1:
    • All pressure systems within their control are thoroughly examined to the prescribed timescale by a competent third party inspector in accordance with the WSE; and
    • Written operating instructions, either from the manufacturer or produced "in-house", are available for operators of the system
  • 4.2.8 Ensure that details of any major modifications to non-exempt pressure systems are passed on to the local SHE Group so that the WSE can be modified accordingly.
  • Line Managers shall (for gas supply systems only):
  • 4.2.9 Ensure that gas bottle regulators on systems they are responsible for are serviced/refurbished or replaced at five years of age. This is independent of the material of construction, and includes regulators on mobile gas bottles that are connected via flexible hose to deliver gas for a short period of time. In exceptional circumstances specific exemptions to this responsibility may be agreed in writing by the Pressure/Vacuum Systems Nominated Engineer and/or Statutory Pressure Systems Inspector.
  • Line Managers shall (for protective devices, such as pressure relief valves and drop/lift plates , fitted to protect exempt pressure systems or vacuum systems):
  • 4.2.10 Ensure that such protective devices are: 
    • Registered with SHE Group
    • Regularly examined in accordance with a written scheme of examination.
4.3 Pressure/Vacuum System Design Engineers shall:
  • 4.3.1 Ensure that when designing pressure or vacuum systems they:
    • Eliminate hazards and reduce risks as far as reasonably practicable.
    • Carry out a suitable and sufficient Design Risk Assessment.
    • Design to an applicable design code.
    • Produce manufacturing information to BS8888.
    • Compile a technical file.
    • The technical file should contain as a minimum the information specified in Appendix 2.2.
  • The design shall conform to the HSE approved code of practice L122 - Safety of pressure systems, Pressure Systems Safety Regulations 2000 - Approved Code of Practice. 
    For systems supplied on a commercial basis this is achieved by designing the system in accordance with the Pressure Equipment Regulations 1999 (PER).
    For systems that are being supplied internally it is strongly recommended that PER is used as guidance - as this enables STFC to meet its obligations under PSSR2000.
    For guidance on the particular steps that should be taken in the design process, or on who to consult, please see the flow chart in Appendix 3.
  • 4.3.2 Whilst recognising that the design applications encountered by STFC are at the cutting edge of technical developments and often unique where it is not practicable to design to a recognised design code:
    • Specify an adequate testing procedure to demonstrate required safety factors; and
    • Ensure that other risk control measures be included in the design (e.g., vacuum chambers with thin windows fall outside of design codes and need a more stringent design risk assessment) to adequately control the risk to persons from system failure; and
    • Where possible ensure that those other control measures be tested to determine the fatigue life and safe operating limit.
  • Consequently, there may be situations where it is impractical to go through all the relevant assurance requirements of PER for such systems. In such cases, the Pressure/Vacuum System Design Engineer should assess the need for full assurance and document alternative action.
  • 4.3.3 Ensure that, where appropriate - either due to the level of risk involved or when a system is being provided on a commercial basis, independent third party inspection or verification takes place at the required stages of manufacture of a vessel, and inform the Pressure/Vacuum system Nominated Engineer that this inspection or verification is taking place.
4.4 Pressure/Vacuum System Nominated Engineers shall:
  • 4.4.1 Approve all designs of pressure and vacuum systems designed and constructed "in house" for their nominated department(s). Prior to manufacture provide manufacturers with documented evidence of this approval.
  • 4.4.2 Approve any major modification to an existing system before the modification is made.
  • 4.4.3 Witness proof tests carried out on new pressure vessels put into service in their nominated department(s).
  • 4.4.4 Ensure that, where appropriate - either due to the level of risk involved or when a system is being provided on a commercial basis, independent third party inspection or verification takes place at the required stages of manufacture of a vessel.
  • 4.4.5 Assess and approve for use, pressure and vacuum systems brought in by facility users or others for use on STFC sites. See Appendix 4 for further guidance on such equipment.
4.5 Technicians who work on Pressure/Vacuum Systems shall:
  • 4.5.1 Ensure that any work they do on a pressure or vacuum system is carried out in line with the relevant drawings and specifications.
  • 4.5.2 Ensure that any protective devices are set to the correct relief pressure - defined by the system specification - before a system is passed over to an end user.
  • 4.5.3 Ensure that all maintenance on a pressure or vacuum system is documented, either electronically or on paper.
  • 4.5.4 Ensure that any modifications or changes involving cutting or welding on a system are designed and approved by the relevant Vacuum/Pressure Systems Design engineer and Vacuum/Pressure Systems Nominated Engineer.
  • 4.5.5 Ensure that any unexpected failure of a pressure or vacuum system under test is suitably investigated before re-testing, and details of any unexpected failure mode fed back to the designer.
  • 4.5.6 Ensure that a catastrophic failure of a pressure or vacuum system under test which led, or could have led to injury or damage to property, is reported as an incident to their line manager and in SHE Assure, see SHE Code 5 (Incident reporting and investigation).
  • 4.5.7 Ensure that control measures, such as the use of warning signs, are adopted to make staff aware of the local hazards when pressure and vacuum systems are being used. 
4.6 Pressure System Permit Issuers shall:
  • 4.6.1 Only issue Pressure System Permits where they are competent to do so, having successfully completed training identified in Appendix 6. They shall not issue permits for work they are going to carry out themselves unless this has been countersigned by another Pressure System Permit Issuer.
  • 4.6.2 Assess all associated risks involved in the proposed work on steam systems, or on entering a pressure vessel, develop a safe system of work and issue a Pressure System Permit, ensuring all necessary precautions, including emergency procedures are taken, and all other appropriate permits (e.g. Confined Space or Hot Work - even though much of the information may be duplicated) have been taken out and issued by an appropriate person, see Appendix 5 for a sample Pressure System Permit.
  • 4.6.3 Oversee the issue of any permit and its cancellation and check safety at each stage of the work.
4.7 SHE Group shall:
  • At some STFC sites these responsibilities may be undertaken by other groups.

  • 4.7.1 Ensure that records of all non-exempt pressure systems on STFC sites are maintained and each system is issued with a unique plant reference number. The records should include the information given in Appendix 2.3.
  • 4.7.2 Ensure that competent third party inspection providers are appointed to undertake a programme of statutory examinations in accordance with the WSE.
  • 4.7.3 Ensure that line managers are advised of any remedial work or alterations that are identified during a thorough statutory examination and are considered necessary for the continued safe operation of the system.
  • 4.7.4 Provide assistance with interpretation of the requirements of this code.
4.8 Staff, tenants, facility users or visitors wishing to use pressure or vacuum systems shall:
  • 4.8.1 When using such systems follow documented safe systems of work, and where necessary to continue using the system safely, seek assistance or clarification from their line manager or supervisor.
  • 4.8.2 Report as an incident (or near miss), following STFC SHE Code 5 (Incident Reporting and Investigation) any instances where:
    • A working pressure system fails catastrophically:
    • A protective device on a pressure or vacuum system activates whilst the system is in use, for example failure of a bursting disc (unless the activation occurs as part of normal operations, e.g. a pressure relief valve on a Liquid Nitrogen dewar); and
    • A vacuum system fails catastrophically, for example a window on a vacuum system fails whilst the system is in use.
  • 4.8.3 When working with facility users who wish to bring a pressure or vacuum system to STFC for use in an experiment, request details about that system, and pass those onto the Nominated Engineer for initial assessment. See Appendix 4 for a list of the information to request.

5. References

  • 5.1 Electronic copies of legislation, approved codes of practice and British Standards can be accessed by STFC staff through ‘Info4Education' further details of which can be found on the SHE Group website.
  • 5.2 L122 - PSSR 2000 ACoP, HSE
  • 5.3 PER - The Pressure Equipment Regulations 1999
  • 5.4 UKSPEC - UK Standard for Professional Engineering Competence, Engineering Council
  • 5.5 BS8888:2008 - Technical Specification, BSI
Relevant BCGA (British Compressed Gas Association) design codes
  • - Industrial Gas Cylinder Manifolds & Distribution Pipework/Pipelines (excluding acetylene). Revision 3: 2005
  • - The Repair of Hand-held Blowpipes & Gas Regulators used with Compressed Gases for Welding, Cutting & Related Processes. Revision 2: 2004
  • - The Safe Storage, Handling & Use of Special Gases in the Micro-Electronics Industry. Revision 2: 2005
  • - Application of the Pressure Systems Safety Regulations 2000 to Industrial and Medical Pressure Systems Installed at User Premises. Revision 1: 2002
  • - Application of the Pressure Systems and Transportable Gas Containers Regulations 1989 to Operational Process Plant: Revision 1: 2004
  • - Bulk Liquid Carbon Dioxide Storage at Users' Premises. Revision 2: 2004
  • - Transportable Vacuum Insulated Containers of not more than 1000 litres volume: Revision 1: 2004
  • - Vacuum Insulated Tanks of not more than 1,000 litres volume which are Static Installations at User Premises: Revision 1: 2004
  • - The Safe Use of Liquid Nitrogen Dewars up to 50 litres: 2000
  • - Safe Storage and Use of Cylinders in Mobile Workshops and Service Vehicles
  • - The Bulk Storage of Gaseous Hydrogen at User's Premises. 2005
  • - The Application of the Pressure Equipment Regulations to Customer Sites: 2003
Relevant British Standards
  • British Standards:2009 Specification for unfired fusion welded pressure vessels
  • BS EN 12952:1-16:2001+ Water tube boilers and auxiliary installations
  • BS EN 13445:1-8:2009 Unfired Pressure Vessels
  • BS EN 13480:1-8:2002+ Metallic Industrial Piping
Relevant STFC Safety Codes

Electronic copies of legislation, approved codes of practice and British Standards can be accessed by STFC staff through STFC-wide subscriptions for online information resources. These services are provided by the Chadwick and RAL libraries and further details can be found on the SHE Grou​p website.

Contact: Baker, Gareth (STFC,DL,COO)