Beta This is a new way of showing guidance - your feedback will help us improve it.

The pressure systems and transportable gas containers regulations 1989

OC 308/13

This OC provides advice on the design aspects of the Pressure Systems and Transportable Gas Containers (PSTGC) Regulations. These aspects of the Regulations (Regs 4 – 7) are relevant only for pressure equipment placed on the market before the Pressure Systems Safety Regulations 2000 came into force, since the design requirements of PSSR are not retrospective.  


1 The PSTGC Regulations came fully into force on 1 July 1994.  On 1 September 1996, the Carriage of Dangerous Goods (Classification, Packaging and Labelling) and Use of Transportable Pressure Receptacles Regulations 1996 (CDGCPL) revoked Part V of the PSTGC Regulations which covered transportable gas containers (now called transportable pressure receptacles (TPRs)). The requirements for TPRs are now covered by CDGCPL 2009 (as amended).


2 The PSTGC Regulations have been revoked and replaced by PSSR 2000.  This OC provides advice on the design aspects of the Pressure Systems and Transportable Gas Containers (PSTGC) Regulations. These aspects of the Regulations (Regs 4 – 7) are relevant only for pressure equipment placed on the market before the Pressure Systems Safety Regulations 2000 came into force, since the design requirements of PSSR are not retrospective.

3 The Simple Pressure Vessels (Safety) Regulations (SPVR) 1991, as amended, are concerned with the manufacture and supply of new welded pressure vessels containing air or nitrogen at a pressure greater than 0.5 bar but less than 30 bar. The SPVR are more limited in their scope than PSSR, as well as being primarily concerned with the initial integrity of vessels rather than their safe use. Manufacturers must, however, provide instructions which cover maintenance and installation for vessel safety. Further guidance on the application and enforcement of the SPVR is in the FOD guide to the inspection of the manufacture and supply of products and substances(chapter 4.2).

Regulation 2 - Interpretation

Pressure system

4 The definition in reg.2 of the PSTGC Regulations has 3 clauses: (a), (b) and (c) which should be read as alternatives. As a consequence of CDGCPL, definition (b) of a pressure system has been amended to read:
'....the pipework with its protective devices to which a transportable pressure receptacle is, or is intended to be, connected; '.

Regulaton 3 - Application and duties

Application and exceptions

5 The PSTGC Regulations apply to pressure systems, as defined, which are used or intended to be used at work. Equipment solely used in domestic premises is not covered. Commentary on particular exceptions is contained in Appendix 1.


6 Duties relate to activities at work, but this covers also the self-employed, for example a self-employed installer of a pressure system (reg.3(2) refers).

7 Regulation 3(3) defines the limits within which designers, suppliers, manufacturers and importers of pressure systems are required to work. Each of them has obligations which extend to any pressure system or any component of any pressure system, but only in the course of trade, business or other undertaking. However, such obligations only apply to matters within the direct control of the designer or manufacturer. The activity does not have to be undertaken for profit.

Regulation 4 - Design, construction, repair and modification

8 Regulation 4 has a number of provisions with which a designer must comply. The design of any pressure system, as well as any component part, will need to address the prevention of danger, and the danger envisaged in reg.4 is that of system failure. A designer will need to consider the purpose and use of the plant and consequently, the characteristics of the contents insofar as they could cause, or accelerate, system failure. National and international design standards provide a sound basis for the design of any new pressure plant.

9 It is permissible to have protective devices other than pressure-relieving devices to meet the standard of reg.4(5). In this regard, note must be taken of the ACOP, which encourages the use of pressure-relieving or pressure-limiting devices to meet reg.4(5). For instruments and/or control equipment to be protective devices, they need to provide an equivalent overall level of safety.

10 Regulation 4(6) is self-contained and imposes wide responsibilities on people, including 'users', who modify or repair systems. Where substantial modifications or repairs are carried out, 'users' who do not have the relevant competence in-house will need to consider using a CP before and after modifications etc.

11 Inspectors should discuss the requirements of the PSTGC Regulations reg.4 and the HSW Act s.6 with designers, manufacturers, importers or suppliers as appropriate. Inspectors should keep in mind that  the PSTGC Regulations  are only applicable for equipment manufactured before PSSR 2000 came into force.  In keeping with the general rule that EC law takes precedence over domestic law, inspectors should seek compliance with the SPVR rather than reg.4 where the former applies.

Regulation 5 - Information and marking

12 Regulation 5 applies to pressure systems designed, supplied, modified or repaired, including second-hand systems. The intention is that information should be adequate to enable users to operate, maintain and examine their plant safely. The quality of information the designer or supplier provides is also important to second-hand pressure systems; in particular, the information should be sufficient to ensure fitness for purpose and continued use. Formal enforcement action may be appropriate where plant has been supplied in a poor state and with insufficient information or marking provided.

13 Basic information about pressure vessels should be permanently marked on the vessel. In some installations, such as low-temperature or insulated pressure vessels, these marks may become obscured, ie iced-up or covered by insulation. Where it is necessary for the information to be readable at all times, the ice or insulation should be removed. Alternatively, fixing the marking plate to a bracket which is proud of the vessel itself can achieve this. Furthermore, the supporting documentation for the vessel should be available.

14 Regarding the design temperature specified in Schedule 4, steam boiler nameplates should indicate the steam saturation temperature corresponding to the design pressure. The design temperatures for other pressure vessels in the boiler system should also be marked, either on each vessel or on a separate plate carrying the temperatures of all the individual pressure vessels. Additionally, the boiler design literature should also show these criteria.

15 Nameplates for hot water boilers should indicate the design outlet water temperature.

Regulation 6 - Installation

16 The PSTGC Regulations do not specifically define the term 'installation'. However, reg.6 applies to any pressure system at work irrespective of whether it is designated as a mobile or an installed system. Regulation 6 is concerned with the positioning and setting up of a pressure system at the location of use. The installer's objective is to maintain the integrity of the pressure system following manufacture and prior to handing over to the 'owner' or 'user'.

17 For most categories of simple pressure vessels, the SPVR require that vessels be accompanied by manufacturer's instructions which cover, amongst other things, the installation requirements for vessel safety. Other sources of information on installation include national standards.

18 The sole responsibility under reg.6 belongs to the employer of any person who installs a pressure system at work. When apportioning legal responsibilities for non-compliance, the contract terms will need to be distinguished carefully, especially if more than one installation contractor is involved and when the installer is working under the direct control of the 'user'.

Regulation 7 - Safe operating limits

19 Regulation 7 prohibits the use of a pressure system unless the 'user' has determined the safe operating limits (SOLs). The SOL may be a design limit (ie specified by the designer or manufacturer), or an operating limit (ie established by the 'user' with regard to the circumstances of actual use, in consultation, where appropriate, with the manufacturer, CP or other organisation with appropriate technical expertise). It is not necessary to engage a CP to carry out a detailed inspection and assessment unless no information is available about the limits and/or the actual condition of the system. For instance, with second-hand plant, it will be important to make sure that the condition of the plant is appropriate to the duty ascribed.

20 The 'user' should have a sound basis for establishing SOLs. Where no information is available about the limit and/or the actual condition of the system, the 'user' should seek suitable advice. However, where the system appears to be unsound, eg not properly maintained, and if the 'user' has not established SOLs, then inspectors should consider formal enforcement action, in consultation with the RSG where appropriate.

October 2011

Appendix 1

Exceptions to the PSTGC regulations

It is important to understand the exceptions contained in Schedule 2. Note that Schedule 2 has been amended by CDGCPL insofar as transportable gas containers are concerned. The PSTGC Regulations Schedule 2 no longer applies to such containers; consult CDGCPL.

Schedule 2 part i

Exception 1(a)

1 The Merchant Shipping Acts 1894 to 1984 were all replaced by the Merchant Shipping Act 1995. The exception covers pressure systems which form part of the equipment of a British or foreign merchant ship. The 1995 Act applies to UK ships, as defined, wherever they are and to non-UK ships while they are in a UK port. Thus the Act can apply not only to those ships that put to sea, but to those used on inland waters.

Exception 3
2 The PSTGC Regulations do not cover the braking, control or suspension systems of road or rail vehicles because they are adequately covered by other statutory provisions. However, vessels forming part of such pressure systems may be covered, as far as initial integrity is concerned, by the SPVR 1991, as amended.

3 The only pressure system excepted is one which serves the braking, control or suspension of the vehicle itself. Pressure systems which control duties other than these vehicular functions are not covered by exception 3, eg the luffing or derricking of the jib on a mobile crane, or the extension or retraction of outriggers.

4 Compressed air systems on quarry vehicles can be of large capacity and high pressure. Working conditions are arduous and corrosion is likely. In quarries, exception 3 is applicable but some of the requirements of the PSTGC Regulations are found in the Mines and Quarries Act 1954 s.84(1). This requires all apparatus which contains air, to be constructed, installed, maintained and used so as to obviate any risk from fire, bursting, explosion, collapse or the production of noxious gases.

Exception 4(a)
5 Compressed air is frequently used to pressurise fabricated structures and components to detect whether their integrity has been compromised or to ensure that repairs have been satisfactorily completed. Leak tests using compressed gases should be undertaken at the lowest practicable pressure. Exception 4(a) is applicable where systems are pressurised above 0.5 bar during leak testing only. This exception does not, however, necessarily cover the test equipment. Pressure systems permanently installed to provide compressed air or gas test media above 0.5 bar will be subject to the Regulations.

Exception 5
6 This exception excludes the low-pressure pipelines used by British Gas as natural gas distribution mains and any similar low pressure gas distribution system. This exception is set at 2 bar subject to the operation of protective devices which can come into use gradually to eliminate the sudden shut-down of supplies. The exception as written in the Regulations makes no such requirement for protective devices.

Exception 6(b)
7 In this case, a pressure system could be associated with an experiment but may be part of a temporary installation. What is temporary will be a matter for inspectorial judgement. Logically, no question of a written scheme will arise because of the short-term nature of the plant, but there should be compliance with other parts of the Regulations so far as is reasonably practicable. It is stressed that, by virtue of regs.7 and 11, experimenters must make an assessment of the safe operating limits of their plant and keep within them.

Exception 7
8 This exception should avoid overlapping requirements which are covered by the Diving at Work Regulations 1997 (file 414).

Exception 8
9 The reference in this exception is now to the Work in Compressed Air Regulations (WCAR) 1996. Whilst the provisions of the WCAR cover the special circumstances of tunnelling and caisson working, ancillary pressure systems, such as mobile compressor units which may be connected on site, will fall within the scope of the PSTGC Regulations. Additional guidance can be found in L96 A guide to the Work in Compressed Air Regulations 1996(file 420).

Exception 9
10 Exception 9 was amended by CDGCPL to take account of the revocation of the Road Traffic (Carriage of Dangerous Goods in Road Tankers and Tank Containers) Regulations 1992 by the Carriage of Dangerous Goods by Road Regulations 1996 (CDG Road). Consequently, a tank as defined in CDGCPL reg.2(1), which includes the carrying tank of a road tanker and a tank container, is exempt from the PSTGC Regulations whilst the CDG Road apply.

11 However, if the tank ceases to be subject to CDG Road, the PSTGC Regulations will apply when a 'relevant fluid' is carried. Pressurised tanks containing non-hazardous materials which are not subject to CDG Road will be 'mobile systems' under the PSTGC Regulations and will need to be examined accordingly.

Exceptions 10 to 12
12 These exceptions relate to international road, rail and sea transportation involving a pressure system. This exception should prevent overlapping requirements which are either covered by other relevant statutory provisions and international agreements, or which are administered by other government departments.

Exceptions 15 to 16
13 These exceptions concerned the application of Part V of the PSTGC Regulations to certain types of storage containers used in the drinks industry. Schedule 2 of the PSTGC Regulations was amended by CDGCPL insofar as it concerned transportable gas containers. Consequently, these types of containers are now dealt with by the provisions in CDGCPL and not the PSTGC Regulations. However, the PSTGC Regulations will still apply to any pipework and fittings to which a transportable pressure receptacle is attached which may form part of such systems.

Exception 18
14 Safe operating limits for refrigeration plants should be specified in the form of maximum and minimum coincident pressures and temperatures. The minimum design temperature is an important design criterion which ensures that materials selected for sub-zero use in refrigerating systems have the required fracture toughness properties at their operating conditions to resist brittle fracture.

15 There is an exception from the Regulations for any vapour compression refrigeration system incorporating compressor drive motors (including standby compressor motors) having a total installed power not exceeding 25kW. No account should be taken of standby motors which may be used as alternatives. The exception would apply to separate systems intended to operate as integrated units by means of electrical connections to one common controller if the total power is below 25kW. This has the effect of bringing within scope medium-sized supermarkets with compressor rooms. However, the Regulations do not cover free-standing display cabinets or the smaller type of industrial refrigeration units. The total installed power value of 25kW represents the lower cut-off point in the Code of Practice published by the Institute of Refrigeration.

Exception 20
16 The exception for prime movers ensures that parts of internal combustion engines and turbines are not covered by the Regulations. Cylinders with an integral piston or ram actuated by steam or compressed air are excepted from these Regulations. Steam locomotives are covered by these Regulations as 'installed systems' thereby making the 'user' specifically responsible for their safety.

Exception 25
17 This exception may be interpreted to cover, for example, portable hand-operated pneumatic road drills; wallpaper strippers; and tools with air-driven motors. Exception 25 only applies to parts of a hand-held tool which are pressure vessels and not to the tool itself.

18 The hand-held lance of an oxy-acetylene welding set is not a pressure vessel because it only 'contains' a 'relevant fluid' in the sense of directing gases to the flame; there is no storage of gas. However, the hand-held lance should be considered part of a pressure system as 'pipework to which a transportable pressure receptacle is, or is intended to be, connected' (reg. 2 refers).

Updated 2020-12-11