Ex h – what it is and how it is used in practice

In many industrial facilities, explosion hazards are primarily associated with electrical equipment. Yet in industrial practice, ignition sources very often originate in purely mechanical components. An overheated bearing, seized gearbox, or metal-to-metal friction can generate enough energy to ignite an explosive atmosphere. Exactly such situations are covered by the Ex h concept in ATEX.

Why Can Mechanical Components Be an Ignition Source in an Ex Zone?

Mechanical components can become an ignition source because they generate heat, sparks, or mechanical energy during operation or failure.

In industrial practice, it’s not about “normal operation” of the device, but about critical situations:

• bearing seizure,
• lack of lubrication,
• shaft misalignment,
• contact of metallic elements.

Under such conditions, the following occurs:

• localized temperature rise,
• formation of hot surfaces,
• and in extreme cases – mechanical sparking.

If the surface temperature exceeds, for example, the MIT (Minimum Ignition Temperature) for a given dust or gas, ignition can occur.

For example:

• many organic dusts have an MIT in the range of 400–600°C,
• a dust layer (LIT) can ignite at just 250–350°C.

This means that even a single overheating point in a device can be critical. If you want to expand on this topic, read about what MIT and LIT are on our blog.

What Is Ex h ATEX and When Does It Apply?

Ex h ATEX is a method of assessing the safety of non-electrical equipment in explosion hazard zones.

Unlike well-known designations:

• Ex d,
• Ex e,
• Ex i,

which apply to electrical equipment, Ex h refers to mechanical equipment.

These include, among others:

• gearboxes,
• agitators,
• fans,
• pumps,
• conveyors.

According to standards (such as EN ISO 80079-36 and 80079-37), Ex h analysis involves:

• identification of potential ignition sources,
• assessment of failure scenarios,
• determination of preventive measures.

The key difference is that Ex h does not rely on a single protection method, but on risk analysis of the specific equipment. This means that every device requires an individual approach.

What Scenarios Lead to Ignition in Ex h Equipment?

The most dangerous scenarios in Ex h are those that combine mechanical failure with the presence of an explosive atmosphere.

In practical audits, situations are often encountered that seem harmless at first glance.

For example:

• a bearing operates without lubrication for several hours,
• temperature gradually increases,
• a layer of dust settles on the housing.

At some point, the surface temperature exceeds the LIT for the dust – and ignition occurs.

Another scenario:

• damage to a rotating element causes metal-to-metal contact,
• mechanical sparks are generated; an explosive gas atmosphere is present in the installation.

This is enough to trigger an explosion. Therefore, in Ex h analysis, the key question is not just “is the device working properly?” but primarily: “what will happen when it stops working properly?”

How to Assess Equipment for Ex h in a Facility in Practice

Assessment of Ex h involves analyzing the actual operating conditions of the equipment and possible damage scenarios.

This requires answering several key questions:

• which components can overheat,
• where friction or metal-to-metal contact can occur,
• is spark formation possible,
• what are the ignition parameters of the medium (MIT, LIT, MIE).

In many facilities, the problem is that:

• equipment has been in operation for years without reassessment,
• operating conditions change (e.g., different medium, different temperatures),
• documentation does not account for realistic failure scenarios.

Therefore, Ex h analysis very often reveals situations such as: equipment is formally approved for operation, but not adapted to current process conditions.

If you are unsure whether mechanical equipment in your installation does not constitute a hidden source of ignition, it is worth verifying this in practice. At ATEX Doradztwo, we help assess equipment for Ex h and real explosion risk – not just based on documentation, but on actual operating conditions.

FAQ

What does Ex h mean in ATEX?

Ex h is a designation concerning the safety of non-electrical equipment in explosion hazard zones, based on risk analysis.

Can a bearing be an ignition source?

Yes. An overheated or damaged bearing can reach a temperature capable of igniting dust or gas.

How does Ex h differ from Ex d or Ex e?

Ex h applies to mechanical equipment, while Ex d and Ex e refer to electrical equipment.

Does every mechanical device require Ex h analysis?

Yes, if it operates in an explosion hazard zone. Every device can generate a potential ignition source.

What parameters are critical in Ex h analysis?

The most important ones are:

• MIT – Minimum Ignition Temperature,
• LIT – Ignition Temperature of dust layer,
• MIE – Minimum Ignition Energy.