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.

Body: ISO
Family: Hydrogen
First published: 2008
Latest revision: 2019
Next revision: Under review
Status: current
Access: Paid (ISO store)

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.

Notes & guidance

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), 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 refuelling stations; the whole chain inherits the explosive-atmosphere discipline of ATEX 2014/34/EU and the cybersecurity of 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