A real regulatory gap that is currently being discussed in hydrogen safety circles (IEC TC31, ISO TC197, EU ATEX working groups). The issue arises because modern hydrogen systems operate far outside the assumptions of classical ATEX, yet leakage inevitably creates an atmospheric explosive mixture.

1) The regulatory conflict (simplified)

Hydrogen systems today - Typical H₂ systems:

Parameter	Conventional ATEX assumption	Modern H₂ systems
Pressure	~1–40 bar	350–900 bar (sometimes higher)
Location	Atmosphere	Pressurized closed systems
Hazard formation	External gas release	High-pressure leak → rapid jet release

ATEX was historically written for:

• chemical plants
• refineries
• storage
• pipelines
• …

where gas systems operate close to atmospheric pressure.

2) Why ATEX seems "not applicable"

ATEX Directive 2014/34/EU applies only if: equipment is intended for use in potentially explosive atmospheres under atmospheric conditions.

Atmospheric conditions (definition):

• Pressure: 0.8–1.1 bar
• Temperature: −20 °C to +60 °C

High-pressure hydrogen systems:

• 350–900 bar storage
• inside vessels / piping
• not atmospheric

Therefore inside the system ATEX is not applicable (see Machinery regulation).

3) But the paradox appears at leakage

When a hydrogen system leaks: 1) Gas expands rapidly 2) Pressure drops to atmospheric 3) H₂ mixes with air

Now the conditions become:

• atmospheric pressure
• flammable mixture

ATEX becomes relevant in the surrounding area. This is exactly the interface between two legal "frameworks".

4) Machinery Regulation clarification

EU Machinery Regulation 2023/1230 (Article related to hazardous substances – often referred to via essential requirement 1.5.7)

Key concept: If hazardous substances are inside machinery, the manufacturer must ensure safe containment and operation. Therefore (Inside the machine): ✔ manufacturer responsibility ✔ pressure safety ✔ leak prevention ✔ integrity

5) When ATEX enters again

ATEX applies when possible explosive atmosphere can occur outside the equipment.

Examples:

Situation	Applicable framework
Hydrogen inside vessel (700 bar)	Machinery + Pressure Equipment
Pipe rupture inside system	Machinery
Hydrogen leak forming explosive atmosphere	ATEX Workplace Directive
Equipment installed in classified zone	ATEX equipment directive

Workplace obligation: ATEX Workplace Directive 1999/92/EC

Operator must:

• classify zones
• create Explosion Protection Document
• install suitable equipment

6) Role of Notified Bodies (European Union Notified Bodies for ATEX)

Third-party approval is needed when:

• equipment is intended for use in explosive atmosphere
• category 1 or 2 equipment
• certain protection concepts

In hydrogen systems this appears for example with:

• compressors installed in Zone 2
• valves or sensors located in hazardous zones
• electrical components in H₂ environments

7) The practical approach here

The modern solution used in hydrogen industry is Separation of responsibilities

Scope	Responsible	Regulation
High-pressure hydrogen system	Manufacturer	Machinery + Pressure Equipment
Leakage risk	Risk assessment	Functional safety
Area classification	Operator	ATEX Workplace
Equipment in classified zone	Manufacturer + Notified Body	ATEX Equipment

8) Engineering strategy used in hydrogen systems

1. Design for "no hazardous area" (Most hydrogen installations try to avoid ATEX zones entirely).

Methods:

• ventilated enclosures
• outdoor installation
• leak detection
• forced dilution

Goal: Zone 2 → Non-hazardous. This is widely used in:

• electrolyzers
• H₂ compressors
• fuel cell systems

2. Secondary explosion protection

If zones cannot be avoided so the use of certified equipment (Ex rated), ignition control and electrical and mechanical classification becomes mandatory.

3. Safety layer concept

Hydrogen systems typically apply multiple protection layers:

Layer	Example
Prevention	leak-tight system
Detection	H₂ sensors
Dilution	ventilation
Shutdown	emergency stop
Explosion protection	ATEX equipment

9) The real regulatory gap (currently debated)

The challenge is that:

• ATEX assumes atmospheric systems
• Hydrogen systems operate far above atmospheric pressure

Therefore the safety concept is evolving toward integrated functional safety + explosion protection

Relevant standards being developed:

Standard	Purpose
ISO 19880	hydrogen fueling
IEC 60079-10-1	hazardous area classification
IEC 60079-2	pressurized systems
ISO 19880-1	hydrogen stations safety

10) Practical rule used in industry

A simplified rule engineers often apply Inside system → Machinery + Pressure safety

Outside system → ATEX

11) Key design principle

The most robust philosophy for hydrogen systems is to prevent explosive atmosphere formation rather than rely on explosion protection. This aligns with the hierarchy in ATEX Directive 1999/92/EC

12) Practical example

Hydrogen compressor skid (350 bar):

Element	Regulation
Compressor housing	Machinery
Pressure vessel	Pressure Equipment Directive
Hydrogen leak scenario	ATEX risk assessment
Electrical panel near leak source	ATEX equipment

The correct approach is 1. Manufacturer ensures containment and machine safety 2. Operator evaluates leak scenarios and hazardous zones 3. Equipment in zones is ATEX certified (with Notified Body involvement).

Keep up the good work!

Arpad
veress@exprofessional.com