Detailed design review of the largest H₂ production plant in the Benelux

Context:
For one of the largest green hydrogen production plants in the Benelux, Prohead Engineering carried out an in-depth review of the EPC partner's detailed engineering. The plant starts with an electrolyser capacity of 25 MW, expandable to 100 MW, and is designed for an annual output of ~14,000 t H₂ at full production. Objective: demonstrate technical compliance and make the design robust with a view to future standards and operation.

Scope & methodology:
Our review covered four domains: process (safety), automation, functional safety (SIS) and OT cybersecurity. We worked iteratively with the EPC team, with periodic status meetings and deliverable checks.

1) Process & process safety

• HAZOP & LOPA: full tracing of HAZOP findings to LOPA cases for critical scenarios (electrolyser upsets, compressor/booster, buffer storage, trailer loading bay).
• ATEX conformity (2014/34/EU): update of zoning, equipment selection (gas group/temperature class) and External Influences (environment, corrosion, IP, temperature).
• H₂ venting & dispersion: resizing of vent stacks and optimisation of vent points (height, position, discharge direction) taking into account:
  • the low ignition energy of H₂,
  • the wide flammable range (LEL ~4 % – UEL ~75 %),
  • the high diffusion rate and upward plume formation,
  • with particular attention to air intakes, walkways and ignition sources (hot surfaces, electrical).

• Detection & ventilation: set points, location and redundancy of H₂ detectors aligned with ventilation patterns and maintenance access.

2) Automation

• C&E matrices (trip, shutdown, permissives) derived from HAZOP/LOPA.
• Alarm rationalisation (priority, shelving, annunciation) to prevent alarm flooding and ensure operator response.
• BPCS-SIS interfacing and network segmentation for OT security (see §4).

3) Functional safety (IEC 61508/61511)

• SRSs per SIF (process trips, ESD, blowdown, vent).
• SIL verifications (PFDavg, SFF, HFT, test intervals) with substantiated failure data and proof-test procedures.
• FSA (Functional Safety Assessment) across lifecycle steps: specification → design → verification → pre-commissioning.
• Result: critical SIFs confirmed at SIL 2; testability and maintenance strategy defined.

4) OT cybersecurity (IEC 62443)

• Zone & conduit modelling (levels 1/2/3, DMZ),
• Defence-in-depth measures (RBAC, hardening, patching, logging),
• BPCS/SIS separation, remote access governance and back-up/restore.

Key deliverables (selection):

• Engineering status summary & status presentations (periodic, with action log and decision points).
• HAZOP/LOPA overview with a traceable link to C&E and SRS.
• ATEX file including External Influences evaluation and equipment selection.
• SRS package, SIL verification reports and FSA report.
• OT security architecture and minimum security requirements for suppliers.

Optimisations achieved:

• Venting: stack height/orientation adjusted to ensure dilution < 25 % of the LFL at air intakes and maintenance positions; additional non-return and cold ignition mitigation evaluated.
• Detection/ventilation: detector layout and test access improved; ventilation capacity and intake aligned with plausible leak rates.
• SIF portfolio: ESD/BD logic tightened; proof-test intervals chosen to balance availability and SIL requirements.
• OT segregation: SIS physically/logically shielded from the BPCS and the rest of the OT network; remote maintenance via controlled jump hosts.

Result & added value:
The plant has a traceable, audit-ready safety and security design: ATEX-compliant, SIL-verified and substantiated according to IEC 62443. The review delivered directly implementable design changes (venting, detection, C&E, network zoning) and a clear roadmap towards scaling up to 100 MW and evolving regulations in the hydrogen value chain.