Executive Summary
A green hydrogen production facility at pre-FEED stage required a HAZID study to identify major hazards before detailed design and site layout were finalised. Hydrogen's distinctive flammability, buoyancy, and ignition energy characteristics meant conventional hydrocarbon facility layout assumptions could not be applied directly, making early hazard identification particularly valuable ahead of costly-to-reverse layout decisions. This representative example illustrates HAZID methodology and findings typical of early-stage hydrogen facility siting studies.
Facility Background
The facility was planned to comprise an electrolyser system, compression equipment, and high-pressure gaseous hydrogen storage, with pre-FEED layout drawings showing preliminary equipment placement based on general industrial siting practice rather than hydrogen-specific hazard considerations. At pre-FEED stage, layout remained flexible enough that hazard-driven spacing or configuration changes could be implemented at near-zero incremental cost, in contrast to the same changes being considered after detailed design or construction had progressed.
Hazard Profile
- —Wide flammability range and low minimum ignition energy of hydrogen, meaning even small leaks could present a credible ignition hazard not always anticipated using hydrocarbon facility spacing norms
- —High buoyancy of hydrogen affecting dispersion and potential accumulation behaviour, particularly relevant to any enclosed or semi-enclosed equipment areas in the preliminary layout
- —High-pressure storage and compression equipment introducing both physical explosion (unignited rupture) and fire/explosion (ignited release) hazard categories
- —Material compatibility considerations, including hydrogen embrittlement risk for certain steels under consideration in preliminary equipment specifications
Study Methodology
- 1.HAZID workshop structured around the preliminary process flow and layout drawings, with participation from process, layout, and safety engineering disciplines
- 2.Systematic hazard identification addressing hydrogen-specific flammability and ignition energy characteristics alongside conventional major hazard categories
- 3.Dispersion and accumulation hazard screening, considering hydrogen's buoyancy relative to the preliminary layout's equipment enclosure and spacing assumptions
- 4.Material compatibility flagging for further detailed engineering assessment, distinguishing hazards requiring layout changes from those requiring materials specification changes
- 5.Scenario screening and prioritisation, identifying which flagged hazards warranted carrying forward into a subsequent quantitative study
Key Findings
- —The preliminary layout placed the electrolyser and high-pressure storage areas at a separation distance appropriate for conventional hydrocarbon facilities but insufficient given hydrogen's wider flammability range and lower ignition energy
- —A planned equipment enclosure for compression equipment created a potential accumulation space for buoyant hydrogen releases that had not been considered in the preliminary layout's ventilation assumptions
- —Preliminary equipment specifications for certain high-pressure components used steel grades warranting further hydrogen embrittlement compatibility review before finalisation
- —Several credible high-pressure release and rupture scenarios were flagged as requiring quantitative treatment in a follow-up QRA, given their potential consequence severity
Risk Reduction Measures
- —Site layout revised to increase separation between the electrolyser and storage areas, achievable at near-zero incremental cost given the pre-FEED design stage
- —Compression equipment enclosure design revised to incorporate hydrogen-specific ventilation provisions addressing the identified accumulation concern
- —Flagged material compatibility items referred to detailed engineering for hydrogen embrittlement-specific materials review before equipment specification finalisation
- —Flagged high-consequence scenarios carried forward as defined scope for a follow-up quantitative risk assessment
Lessons Learned
Hydrogen facility layout cannot be safely derived from conventional hydrocarbon facility spacing norms.
The preliminary layout's spacing, while reasonable by general industrial practice, did not reflect hydrogen's specific combination of wide flammability range and low ignition energy — a gap only caught because the HAZID was explicitly structured around hydrogen-specific hazard characteristics rather than a generic checklist.
Pre-FEED stage is when layout hazard findings are cheapest to act on, and this window closes quickly.
The separation distance increase and enclosure ventilation revision were both achievable at near-zero cost specifically because layout remained flexible at pre-FEED stage; the same findings identified after detailed design would have required costly rework.
HAZID's role is to screen and route hazards to the right next step, not to resolve them all at HAZID stage.
Some findings (layout separation) were resolved directly within the HAZID process, others (material compatibility) were routed to detailed engineering, and others (high-consequence release scenarios) were routed to a follow-up QRA — reflecting HAZID's proper role as an early screening and routing exercise.
Technical Takeaways
- —Apply hydrogen-specific hazard criteria (flammability range, ignition energy, buoyancy) explicitly in HAZID rather than relying on generic hydrocarbon facility checklists
- —Prioritise layout-affecting HAZID findings for resolution while pre-FEED design flexibility still makes changes low-cost
- —Flag material compatibility concerns for dedicated detailed engineering review rather than attempting resolution within the HAZID workshop itself
- —Use HAZID findings to explicitly scope follow-up quantitative studies rather than treating HAZID as a standalone, complete hazard assessment