Pressurisation Units & Expansion Vessels RAMS: PSSR Compliance and Risk Assessment Guide

Table of Contents

• Why PSSR RAMS Matter
• Key Hazards in Pressurisation Equipment Installation
• Pressure Systems Safety Regulations 2000 Obligations
• Commissioning Hazards and Controls
• Plant Room Access and Confined Space Considerations
• What Your Pressurisation RAMS Must Cover
• Frequently Asked Questions

Why PSSR RAMS Matter

Pressurisation units and expansion vessels are critical components of closed heating, chilled water, and domestic hot water systems in commercial buildings. Their installation and commissioning involves working with pressurised systems that carry risks of sudden high-pressure release, scalding from hot water, and component failure — risks that must be thoroughly addressed in a compliant RAMS.

Under CDM 2015, contractors installing pressurisation equipment are duty holders who must produce a project-specific RAMS. The additional requirement of the Pressure Systems Safety Regulations 2000 (PSSR) means that the RAMS must also address the written scheme of examination requirements and the competency of the person responsible for commissioning the pressurised system.

This guide explains what a compliant pressurisation units RAMS must include, with particular focus on the commissioning hazards that are most frequently inadequately documented.

Browse all trade RAMS templates on the RAMS AI trade hub — covering 22 specialist construction trades.

Key Hazards in Pressurisation Equipment Installation

• High-pressure release during commissioning — Incorrectly set relief valves, loose connections, or over-pressurisation during system fill and charge can cause sudden high-pressure water ejection. This is the primary injury risk during commissioning and must be addressed in detail in the RAMS.
• Scalding from hot water — Pressurisation units and expansion vessels connected to high-temperature heating systems can contain water at 80-90°C. Any sudden pressure release from such a system risks serious scalding injuries.
• Manual handling of expansion vessels — Commercial expansion vessels can be large, heavy (50-300 kg), and difficult to manoeuvre into plant rooms through restricted access routes. Manual handling assessment must address plant room access routes, door widths, and staircase considerations.
• Plant room access — Plant rooms may be restricted-access spaces with limited headroom, limited ventilation, and the presence of gas appliances (CO risk), energised electrical panels, and hot surfaces.
• Working at height within plant rooms — Plant rooms frequently have mezzanine levels, valve pits, or overhead pipework requiring working at height.
• COSHH from system inhibitor and corrosion treatment products — Heating system inhibitors contain chemicals that are irritating to skin and eyes and must be assessed under COSHH.

Pressure Systems Safety Regulations 2000 Obligations

The PSSR 2000 apply to pressurised systems above specified thresholds (for pressurised hot water above 110°C: any system; for steam: systems above 0.5 bar; for other fluids: systems where pressure × volume exceeds specified values). For commercial heating pressurisation systems, PSSR typically applies to:

• Any pressurisation unit where the system working pressure exceeds 0.5 bar and the fluid is above ambient temperature
• Systems with any component rated above specified limits (check the PSSR Approved Code of Practice — L122)

Where PSSR applies, your RAMS must confirm:

• A written scheme of examination has been prepared by a competent person (typically a chartered engineer or specialist inspection body such as Lloyd's Register or Bureau Veritas)
• The system has been examined at commissioning in accordance with the written scheme
• Examination records are in place and will be maintained for the life of the system
• The duty holder (building owner or operator) has been informed of their ongoing obligations under PSSR

Commissioning Hazards and Controls

Commissioning is the highest-risk phase of pressurisation equipment installation. Your RAMS must specify:

• Pre-commissioning checks — Before pressurising the system, confirm: all connections torqued to specification, pressure relief valve set to correct pressure and direction (discharge directed safely, not towards persons), system fill point valves in correct position, gauge calibration certificate current.
• Pressurisation sequence — Describe the fill and charge sequence in detail: initial fill at low pressure, check for leaks, pressurise incrementally to working pressure, check for leaks at each stage, pressurise to design system pressure, confirm pressure relief valve operation at the set pressure.
• PPE during pressurisation — Specify the PPE for the person conducting commissioning: face shield or splash-proof safety spectacles, waterproof gloves, non-slip footwear. For hot water systems above 60°C, specify steam-rated gloves.
• Exclusion zone — During pressurisation and initial system operation at elevated temperature, specify that a 2-metre exclusion zone will be maintained around all connections and the pressure relief valve discharge point, and that no unprotected persons will be in the zone.
• Emergency shut-down — Specify the location of the system isolation valve and the procedure for emergency shut-down if a leak or pipe failure occurs during commissioning.

Plant Room Access and Confined Space Considerations

Plant rooms housing pressurisation equipment can present confined space risks under the Confined Spaces Regulations 1997 where:

• Ventilation is inadequate and gas appliances create carbon monoxide (CO) risk
• The plant room has restricted access (single entry/exit point, access via hatch or ladder)
• Oxygen deficiency could arise from gas leaks or displacement by refrigerants

Your RAMS must assess whether the plant room constitutes a confined space. If it does, confined space working rules apply: buddy system, atmospheric monitoring, rescue plan, and entry permit. If it does not meet the confined space threshold, still specify ventilation requirements and CO detection where gas appliances are present.

What Your Pressurisation RAMS Must Cover

• System description: pressurisation unit type, expansion vessel size, working pressure, temperature
• PSSR assessment: does PSSR apply? Written scheme reference, competent person for examination
• Manual handling: expansion vessel weight, plant room access route, mechanical handling aids
• Commissioning sequence: pre-checks, fill and charge procedure, PPE, exclusion zone
• Pressure relief valve: set pressure, discharge direction, test confirmation
• Plant room confined space assessment: ventilation, CO detection, entry procedure
• COSHH for system inhibitor: product, controls, PPE
• Emergency shut-down procedure
• CDM pre-start briefing record

Frequently Asked Questions

Who qualifies as a competent person for PSSR purposes?

Under the PSSR 2000, a competent person for the purpose of preparing a written scheme of examination and conducting examinations must have sufficient practical and theoretical knowledge of the specific type of pressure system to detect defects and assess their significance. In practice, this is typically a chartered mechanical engineer with pressure system inspection experience, or an engineer employed by an accredited inspection body (such as those approved by UKAS). The heating contractor installing the equipment is generally not the appropriate competent person for PSSR examination — this must be arranged separately with the building owner or principal contractor.

What happens if the pressure relief valve lifts during commissioning?

An unexpected PRV lift during commissioning indicates that the system pressure has exceeded the PRV set point. Stop pressurisation immediately and investigate the cause before proceeding. Possible causes include: incorrect PRV set point, fault in the pressurisation unit pressure control, excessive fill water temperature causing thermal expansion, or a system fault. Do not re-set the PRV to a higher pressure without the approval of the system designer — the PRV set point is a safety parameter that must not be arbitrarily changed.

Does the building owner need to be present during PSSR examination at commissioning?

Not necessarily present in person, but they must be notified that the PSSR examination is taking place, they must accept the written scheme of examination from the competent person, and they must receive the examination record (certificate of examination) after the inspection. They are also responsible for ensuring that subsequent periodic examinations are carried out in accordance with the written scheme throughout the operational life of the equipment.