# ISO 22734 — Hydrogen generators using water electrolysis

> ISO 22734 is the international standard for hydrogen generators that split water by electrolysis — alkaline, PEM and solid-oxide. It sets the safety and performance requirements for the equipment at the heart of green hydrogen, where flammable hydrogen and oxygen are produced together.

- Source : https://industryhub.site/en/standards/iso-22734
- Body : ISO
- Family : Hydrogen
- Status : current
- First published : 2008
- Latest revision : 2019
- Edition : Consolidated (2019)
- Next revision : Under review
- Access : Paid (ISO store)
- Language : English

## Document structure

- **ISO 22734:2019** — Industrial, commercial and residential applications : The consolidated standard (superseding the former -1 and -2 parts). Defines construction, safety and performance requirements for water-electrolysis hydrogen generators across application sizes.
- **ISO 19880 (companion)** — Gaseous hydrogen fuelling stations : Where electrolytic hydrogen is dispensed to vehicles — the downstream counterpart to ISO 22734 generation.
- **ISO 19884 / ISO 11114 (companion)** — Cylinders & material compatibility : Storage of compressed hydrogen and compatibility of materials with hydrogen (embrittlement) — the storage and transport side.

## Key concepts

- **Electrolysis technology** : Alkaline (mature, low-cost), PEM (proton-exchange membrane — fast-responding, follows variable renewables well), and high-temperature solid-oxide (SOEC — highest efficiency using heat). ISO 22734 is technology-neutral but the hazards and balance-of-plant differ by type.
- **Co-production of hydrogen and oxygen** : Electrolysis splits water into hydrogen and oxygen. Keeping the two gas streams separated, detecting cross-contamination and avoiding a flammable mixture is a core safety requirement — the central reason the standard exists.
- **Hydrogen safety envelope** : Hydrogen has a very wide flammability range and low ignition energy. ISO 22734 requires hazardous-area (ATEX/IEC 60079) zoning, ventilation, gas detection, and safe start-up/shutdown and purge sequences to prevent an explosive atmosphere.
- **Specific energy consumption** : The electricity used per kilogram of hydrogen (kWh/kg), the inverse of efficiency. Systems run around 50-55 kWh/kg today; this number, multiplied by the electricity price, dominates the cost of green hydrogen.
- **Dynamic / flexible operation** : Coupled to solar or wind, an electrolyzer must follow variable power. PEM ramps fast; frequent cycling stresses stacks and the balance-of-plant, so durability under dynamic duty is now a key specification point.
- **System boundary / balance of plant** : An electrolyzer is more than the stack: water treatment, gas separation and drying, power conversion (rectifier), cooling and controls. ISO 22734 addresses the integrated generator, not just the cell.

## The machine at the heart of green hydrogen

Green hydrogen begins with an **electrolyzer**: a machine that uses renewable electricity to split water into hydrogen and oxygen. **ISO 22734** is the standard that governs that machine — its construction, safety and performance — across sizes from a cabinet to a multi-megawatt plant.

The standard exists because electrolysis produces two reactive gases at once: flammable hydrogen and pure oxygen. Keeping them apart and out of an explosive mixture is non-negotiable.

## The three electrolysis routes

ISO 22734 is technology-neutral, but the choice shapes the system:

- **Alkaline** — mature and cheap, the workhorse of large industrial plants.
- **PEM** (proton-exchange membrane) — compact and fast-responding, the best match for **variable** solar and wind input.
- **Solid-oxide (SOEC)** — high-temperature, highest efficiency where waste heat is available, still earlier in deployment.

## Safety: hydrogen and oxygen together

Hydrogen's wide flammability range and low ignition energy make the safety case central. ISO 22734 requires **gas separation** and cross-contamination detection, **hazardous-area zoning** (aligned with ATEX / [IEC 60079](/en/standards/iec-60079)), **ventilation**, **gas detection** and safe **start-up, shutdown and purge** sequences. The same hydrogen properties drive material choices, because the small molecule leaks easily and embrittles some steels.

## Cost, flexibility and the wider stack

Performance comes down to **specific energy consumption** (kWh per kg) — which, times the electricity price, sets the cost of the hydrogen. Coupled to renewables, the electrolyzer must run **dynamically**, and frequent cycling wears the stack. Downstream, the hydrogen is compressed, stored and either used on site or dispensed through [ISO 19880](/en/standards/iso-19880) refuelling stations; the whole chain inherits the explosive-atmosphere discipline of [ATEX 2014/34/EU](/en/standards/atex-2014-34-eu) and the cybersecurity of [IEC 62443](/en/standards/iec-62443) for its controls.

## Applicable industries

Green hydrogen production (power-to-X), Industrial hydrogen users (refining, ammonia, steel), Mobility refuelling (with ISO 19880), Renewable developers coupling electrolysis to solar/wind

## References & further reading

- [ISO 22734:2019 — official](https://www.iso.org/standard/69212.html)
- [IEA — The Future of Hydrogen](https://www.iea.org/reports/the-future-of-hydrogen)