Hydrogen fuel cells as backup power — safety aspects alongside diesel and battery UPS

The [backup generator guide (§551)](/guides/nen-1010/noodstroomaggregaten-551) and the UPS battery types guide cover the two established backup-power technologies: the diesel generator and the battery UPS. This article covers a third option, emerging in data centres and telecom sites: the hydrogen fuel cell, which generates electricity electrochemically (without combustion) from stored hydrogen gas, with a number of safety aspects that differ fundamentally from diesel or a battery.

Why a fuel cell is not simply a diesel generator with a different fuel

A diesel generator burns fuel in a combustion engine; a PEM fuel cell (Proton Exchange Membrane, the most common design for this power range) lets hydrogen and oxygen from the air react electrochemically across a membrane, without a flame or combustion process, producing only water as a reaction product. Yet the safety task is not smaller than with diesel — it merely shifts from fuel safety (a flammable liquid) to gas safety (a gas with an exceptionally wide flammability range and very low ignition energy).

Hydrogen hazard: why it differs from natural gas or LPG

Hydrogen has properties that require targeted measures, independent of the fuel-cell technology itself:

A very wide flammability range in air (roughly 4% to 75% volume concentration), much wider than natural gas or LPG.
A very low minimum ignition energy — significantly lower than most hydrocarbon gases, meaning even small static discharges can cause ignition.
A very low density, causing a leak to dilute rapidly upward and accumulate at ceilings or high points of a room, rather than spreading along the floor as with LPG.

This combination requires targeted measures: ventilation (natural or mechanical) specifically aimed at high points of the installation room rather than floor-level ventilation alone, and hydrogen detectors set to a percentage of the lower explosive limit (LEL) with staged alarming (for example a warning level at 25% LEL and a shutdown level at 50% LEL).

PGS 35 — the Dutch guideline for hydrogen installations

In the Netherlands, PGS 35 (Publicatiereeks Gevaarlijke Stoffen) specifically regulates the storage and use of hydrogen, with requirements for storage pressure, piping, ventilation, detection and emergency shut-off provisions. This is an additional, hydrogen-specific layer on top of the generic electrical requirements of NEN 1010 — a fuel-cell installation must comply with both: the electrical connection, earthing and separation via NEN 1010, and the hydrogen storage/piping via PGS 35.

Hazardous-area classification around a fuel-cell installation

Despite a fuel cell being primarily regarded as an electrical power source, the environment around the hydrogen storage, piping and possible leak points can require a hazardous-area classification under NEN-EN-IEC 60079-10-1, just as with any other flammable-gas application. Electrical equipment within that zone — including cable entries, switchgear and luminaires — must then comply with the relevant Ex protection method for that zone, even though the fuel cell itself is installed precisely to supply electricity rather than consume it.

Response time: why a battery buffer remains necessary

A fuel cell, unlike a battery UPS, does not respond instantaneously to a sudden load step: the electrochemical process and the associated gas regulation have a start-up and control time in the order of seconds, comparable to — and sometimes slower than — the step-load acceptance time of a diesel generator covered in the guide on generator step-load acceptance (ISO 8528-5). For a critical load that must not experience any interruption at all, a battery buffer between the fuel cell and the load therefore remains necessary — in that architecture, the fuel cell replaces the role of the diesel generator (a sustained energy source that replenishes/ supports the battery), not the role of the battery itself (the instantaneous bridging).

Practical relevance

When assessing a fuel-cell installation as backup power, it must be verified that, besides the regular electrical commissioning (connection, earthing, separation per NEN 1010), PGS 35 has also been satisfied for the hydrogen storage and piping, that a hazardous-area classification has been carried out for the environment of any leak points, and that the system architecture includes a battery buffer that genuinely covers the bridging time until full fuel-cell response — rather than assuming the fuel cell behaves like a battery.

Common mistakes

Treating the installation room as an ordinary diesel-generator room without hydrogen-specific ventilation at high points and staged gas detection.
Assuming a fuel cell responds instantaneously to a load step like a battery — without a battery buffer, a noticeable interruption time arises on a sudden load increase.
Not carrying out a hazardous-area classification around piping and storage, on the argument that it is a power source — the ignition risk is determined by the hydrogen, not by the function of the equipment.
Confusing PGS 35 with the generic ATEX directive — PGS 35 specifically regulates the hydrogen storage and use installation in the Netherlands; a correct hazardous-area classification per NEN-EN-IEC 60079-10-1 remains additionally necessary for the electrical equipment in the vicinity.