When the substance changes: why equipment may need a new ATEX assessment

The article in brief

• Equipment used in potentially explosive atmospheres is marked for a specific type of atmosphere and, for gases and vapours, a specific gas group [1] [6].
• If the substance in a process is changed, it can affect which equipment may be used, even when the rest of the facility is unchanged.
• Equipment for a higher gas group can normally be used where a lower one is sufficient, but not the other way round [5]. One example is a change from methane (IIA) to hydrogen (IIC) [2] [3].
• Equipment for dust is marked D and is not assessed for gas, so a change between gas and dust requires a completely new assessment [6].
• The explosion protection document must be updated when significant changes are made [7].

ATEX is the EU regulatory framework for equipment and workplaces where an explosive atmosphere may occur. Facilities change over time: fuels are switched, process gases are changed or new raw materials are introduced. The ATEX assessment of the equipment then needs to be reviewed, because it applies to a specific substance. A clear example is a transition from methane to hydrogen, where equipment may need to move from gas group IIA to IIC.

Why the question is becoming more common

The transition to fossil-free energy brings new substances into industry, and existing ones are replaced or blended. Hydrogen replacing fossil fuels and feedstocks is a typical case. A facility is often built and assessed for a different substance than the one it will handle in future, and the differences only become clear when the change is made.

What do IIA, IIB and IIC mean?

Equipment for explosive gas atmospheres is divided into gas groups IIA, IIB and IIC according to how easily the gases ignite. IIC is the most demanding group. The properties of a gas are determined under the standard IEC 60079-20-1 [1]. The group is stated in the equipment marking together with a temperature class, which shows the maximum permitted surface temperature.

IIC equipment can normally also be used where a lower group is sufficient, but the reverse does not apply [5]. A component marked for IIA can therefore not automatically be used once a substance in a higher group is introduced into the process.

The marking also shows which type of atmosphere the equipment is intended for. G stands for gas, vapour or mist, and D stands for dust [6]. Vapours from flammable liquids therefore fall under G and are covered by the gas groups. Equipment marked for dust is not assessed for gas, so a change between gas and dust requires a completely new assessment, and not only a different gas group.

Example: from methane to hydrogen

Methane, the main component of natural gas, belongs to gas group IIA and hydrogen belongs to IIC [2] [3]. The minimum ignition energy is about 0.28 millijoules (mJ) for methane and about 0.02 mJ for hydrogen, which is more than ten times lower [3] [4]. The flammable range is about 4 to 17 percent by volume for methane and 4 to 77 percent by volume for hydrogen [2] [3].

Both gases belong to temperature class T1, the least demanding class, with a maximum surface temperature of 450 °C [3] [4]. Equipment suitable for methane can therefore have the right temperature class but the wrong gas group. For other substances it can be the other way round, so the temperature class always needs to be checked together with the gas group.

Blends and in-between cases

Many facilities do not go straight from one substance to another, but blend in the new one step by step. The gas group then depends on the composition. A published study of methane and hydrogen shows that up to 10 mol% hydrogen has hardly any effect on the safety characteristics. The blend falls in IIB above about 25 mol% hydrogen and in IIC only above about 75 mol% [2]. The figures are approximate, so the group should be determined under the standard for the specific blend in use [1] [2].

What should be reviewed when the substance changes?

The gas group is a good starting point, but the review covers more:

• Marking and certificates: equipment in hazardous areas, such as motors, sensors and luminaires, must have the right type of atmosphere (G or D), gas group and temperature class for the new substance.
• Zone classification: a new substance can behave differently in a release. Hydrogen, for example, is very light, with a density of about seven percent of that of air [4], and has a wide flammable range. The extent of the zones therefore needs to be reassessed.
• Protective measures: ventilation, gas detection and other measures designed for the previous substance need to be checked against the new one.
• Maintenance: maintenance and spare-parts procedures need to ensure that components are replaced with equipment of the right group.

A common example is an electric motor or a sensor on a pipeline. If it is marked for IIA, it was right for methane, but for hydrogen an IIC design is needed.

How to handle the change

Directive 1999/92/EC requires the employer to keep a current explosion protection document and to update it when significant changes, extensions or conversions are made [7]. A change of substance should lead to a new review.

A workable approach is to involve ATEX expertise already when the change is being planned. This leaves room to choose solutions such as replacing individual components with a version for a higher gas group, adjusting the zone classification or adapting the process, before purchases and schedules are fixed. The change is best linked to the existing management of change (MoC) process and to risk analyses such as HAZID and HAZOP.

How ProSa can help

ProSa works with ATEX classification, explosion protection documents and risk analysis for facilities that change substance or modify their process. Read more about our ATEX services or get in touch for an initial discussion.

Conclusion

A new substance gives explosion protection a new starting point. Equipment may need a different gas group, a different temperature class or an entirely different type of assessment, and the zone classification, protective measures and explosion protection document need to be reviewed in the same effort. Methane replaced by hydrogen is a clear case, but the principle applies to any change in what is handled. Those who raise the question early have the best chance of choosing solutions that are both safe and practical to implement. Feel free to get in touch if you are facing a change.

References:
[1] IEC 60079-20-1 (equivalent to ISO/IEC 80079-20-1), Explosive atmospheres, Part 20-1: Material characteristics for gas and vapour classification, Test methods and data.
[2] Askar, E., Schröder, V., Schütz, S., Seemann, A. (2016). Power-to-Gas: Safety Characteristics of Hydrogen/Natural-Gas Mixtures. Chemical Engineering Transactions, 48, 397 to 402. CET.
[3] Thedens, M., PTB (2024). IEC TC 31 standards for Ex Equipment, standardisation for the hydrogen economy. Presentation, IECEx. IECEx.
[4] Danielsson, J., Gexcon (2021). Fysikaliska risker vid vätgashantering (Physical hazards in hydrogen handling). Presentation at Gasdagarna, Energigas Sverige, 27 May 2021. Energigas Sverige.
[5] Thurnherr, P. (2018). Electrical Installations: Design, Selection, Erection and Inspection (section Selection according to equipment grouping). Presentation, IECEx International Conference, Jakarta. IECEx.
[6] Directive 2014/34/EU of the European Parliament and of the Council on equipment and protective systems intended for use in potentially explosive atmospheres, Articles 2 and 16 and Annexes I and II. EUR-Lex.
[7] Directive 1999/92/EC of the European Parliament and of the Council of 16 December 1999 on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres, Article 8. EUR-Lex.