Can Ex equipment be used above +40 °C ambient, for example in the Middle East?

Yes, but only equipment that is certified and marked for a higher maximum ambient temperature, for example -20 °C ≤ Ta ≤ +55 °C or -20 °C ≤ Ta ≤ +60 °C. Equipment rated for the normal range of -20 °C to +40 °C has its temperature class and its type of protection proven only up to +40 °C, so it must not be used where the local ambient can exceed that, in the Middle East or anywhere else.

Short answer

• The default rating ends at +40 °C. IEC 60079-0 treats -20 °C to +40 °C as the normal ambient range; anything else is a special range that the manufacturer must state and mark (from edition 8, 2026, the range is marked in every case).
• Above the rated maximum, the T-class is no longer proven. The maximum surface temperature is determined at the maximum rated ambient, so every extra degree of ambient raises the hot surfaces too.
• Only the manufacturer and the certificate can extend the range. A user cannot re-rate certified equipment by calculation, by derating the load or by an engineering judgement. (Uncertified simple apparatus in intrinsically safe circuits is the exception: IEC 60079-14:2024 Annex Q gives its temperature assessment, with permitted power falling as the ambient rises.)
• Extended ranges often cost a temperature class. Certificates commonly give a table such as T6 up to +40 °C and T5 or T4 up to +55 °C or +60 °C; the class that applies is the one for your ambient line.
• The design ambient is the local air temperature at the equipment, which in sun, inside shelters or near hot plant can be well above the published shade temperature.

Why +40 °C is a hard limit on a standard rating

IEC 60079-0, the general requirements standard for Ex equipment, says that equipment is normally designed for -20 °C to +40 °C and that equipment designed for any other range is "special": its range must be stated by the manufacturer and marked as Ta or Tamb with the limits, or covered by the symbol X on older certificates. The European Commission's ATEX Guidelines (6th edition, January 2026) say the same from the legal side: electrical products are normally designed and tested for -20 °C to +40 °C under the harmonised standards, and products for use outside that range need additional marking and testing, normally agreed between manufacturer and user.

The reason is physical. The standard requires the maximum surface temperature, and the service temperatures of seals, insulation and cable entries, to be determined with the equipment at its maximum rated ambient. A luminaire, motor or junction box whose hottest point runs 90 K above its surroundings reaches about 130 °C at +40 °C but about 145 °C at +55 °C (illustrative values, as a working approximation for equipment without a temperature-limiting device). If it was marked T4 (135 °C limit), it is no longer T4 in that location, and nothing on the label tells you so.

Surface temperature is not the only issue. Gaskets, cable gland seals, encapsulation compounds, batteries and electronics were assessed only up to the rated maximum. The certificate proves explosion protection within its range; it says nothing about how the item behaves, or how long it lasts, beyond it. The US Coast Guard's guidance on markings gives a plain example: equipment without an ambient marking is safe only within the normal range up to +40 °C and would not be safe in a classified location with a +48 °C ambient, whatever its temperature class.

How hot is "ambient" on a Gulf project?

The World Meteorological Organization has verified 53.9 °C at Mitribah, Kuwait (21 July 2016) as one of the highest temperatures ever recorded on Earth. Design values for a project are set by the client's specification from local meteorological data, not by the Ex standards. Two points matter for the equipment:

• Ta is the air around the equipment, not the weather station reading. Equipment inside an unventilated shelter, a cabinet or next to hot pipework sees a higher ambient.
• Solar radiation adds heat. IEC 60079-14 (edition 6, 2024) deals with UV and solar radiation for cables and has an informative annex on adverse environmental conditions that includes solar radiation. Sunshades, light-coloured surfaces and correct orientation help; whether solar gain must be added to Ta is covered in a separate question below.

How to select equipment for a high ambient

1. Fix the design ambient for each location with the project team, including sun, shelters and nearby heat sources.
2. Read the certificate, not only the nameplate. Look for the ambient range and, where there is a table, the temperature class that goes with each range.
3. Check the T-class against the gas at that line. For hydrogen sulphide (autoignition 260 °C, T3) a T4 line at +40 °C is irrelevant if the site needs +55 °C; you need at least T3 at +55 °C.
4. Check the accessories too. Cable glands, cables, breathers and plugs have their own temperature ranges. If the equipment marking calls for heat-resistant cable (entry point above 70 °C or branching point above 80 °C at the rated ambient), select accordingly.
5. If nothing suitable exists, reduce the local ambient (ventilated or air-conditioned shelter, relocation) or ask the manufacturer whether a certified variant with a wider range is available.

Common mistakes

• Treating +60 °C as the normal range. IEC 60079-0 mentions -20 °C to +60 °C as the atmospheric conditions for the explosive atmosphere in its scope; the normal equipment range is still -20 °C to +40 °C.
• "Derating" on site. Running a motor or heater at reduced load does not change its certificate; only a certified rating does.
• Using the monthly mean or shade temperature instead of the worst local air temperature at the mounting point.
• Forgetting the cable entry. At high ambient the gland and cable may be the weakest part.

Related on excodex

• Ambient temperature range Ta: what -20 °C to +40 °C really means
• Temperature classes T1 to T6: matching surface temperature to autoignition temperature
• Does solar radiation count when checking the ambient temperature Ta?
• Why does a certificate list different temperature classes for different ambient temperatures?
• If no ambient temperature is marked, what range does the equipment cover?

Standards and further reading

• IEC 60079-0, general requirements for Ex equipment: normal ambient range, special ranges and their marking, determination of surface temperature at maximum ambient (edition 8, 2026). Clause wording paraphrased from the public copy of the 2004 edition: law.resource.org (PDF)
• IEC 60079-14:2024, design, selection and installation, with selection according to temperature range and an annex on adverse environmental conditions (contents in the preview): standards.iteh.ai (PDF)
• European Commission, ATEX 2014/34/EU Guidelines, 6th edition (January 2026), note on atmospheric conditions and the -20 °C to +40 °C design range: single-market-economy.ec.europa.eu (PDF)
• US Coast Guard OCS National Center of Expertise, Drill Down 27, temperature class and ambient marking: dco.uscg.mil
• World Meteorological Organization, verification of 53.9 °C at Mitribah, Kuwait: wmo.int

This article is general technical information prepared by the excodex editorial team. It does not replace the applicable standards, the equipment certificates and instructions, national regulations or the assessment of a competent person.