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Guide · Gas detection · Hazardous-location approvals

What is the ATEX equivalent in the US? ATEX vs IECEx, Class I Division 2 (Groups C and D), ATEX Category 2 and Zone 2, the types of explosion protection, and how to read the approval line on a Honeywell BW or MSA gas detector

There is no single US "ATEX". ATEX is a European Union directive; in the United States, OSHA’s 29 CFR 1910.307 requires equipment in a hazardous (classified) location to be intrinsically safe, approved for the location, or safe for it, and it points to NFPA 70 (the National Electrical Code) for the Class, Division and Group system and the alternative Class I Zone system. Approval comes from a nationally recognized testing laboratory listing (UL, CSA, ETL and the like), not from a directive. A gas detector sold here is marked for the US system (for example Class I, Division 1, Groups A, B, C, D) and usually for ATEX and IECEx as well, which is why one Honeywell BW Clip label carries all three.

Bayshore Safety. Industrial safety and PPE supplier since 2017. · Current as of November 2026 · 29 CFR 1910.307 (hazardous (classified) locations; current eCFR, fetched Nov 10 2026) and 1910.399; the approval lines printed in the Honeywell BW Clip, Clip4, Solo and MicroClip data sheets and on the MaxXT II product page and in the MSA ALTAIR 4XR bulletin (0816-102-MC) and ALTAIR io 4 specification sheet (automation.honeywell.com and us.msasafety.com, fetched Nov 10 2026); the IEC 60079 marking scheme as those documents print it
Honeywell BW and MSA detectors, with the approvals each manufacturer printsGas detection selector
BW Technologies BWC2-H Clip H2S Monitor, 10/15 ppm Alarms, 2-yearBW Technologies BWC2-H Clip H2S Monitor, 10/15 ppm Alarms, 2-yearHoneywell BW prints cULus Class I, Div. 1, Gr. A, B, C, D; Class I, Zone 0, Gr. IIC; ATEX II 1G Ex ia IIC T4 Ga; IECEx Ex ia IIC T4 Ga on the BW Clip datasheet
$112.37See the product

Why this question has no one-word answer. ATEX is the name of two EU directives (2014/34/EU for equipment and 1999/92/EC for workplaces); IECEx is an international certification scheme run under the IEC 60079 standards; and the United States has neither. What the United States has is a rule, 29 CFR 1910.307, that says what electrical equipment in a hazardous (classified) location must be, and a code it names, NFPA 70, that classifies the locations by Class, Division and Group (or Class and Zone) and lists the protection techniques. Equipment is then listed by a testing laboratory to the standard that fits (UL 913 for intrinsic safety, UL 1203 for explosion-proof, and others). So the honest answer to "what is the ATEX equivalent in the US" is: the NEC classification system plus an NRTL listing, and on a gas detector that shows up as the Class I, Division 1 line printed beside the ATEX and IECEx lines. This page goes through the questions people ask about the three systems, with the markings Honeywell BW and MSA print on the instruments in the band as the worked examples, and sends you to the live guides on zones and divisions and on intrinsically safe detectors for the parts they already cover.

The questions, one by one

The rule text is 29 CFR 1910.307 as current on the eCFR; the markings are quoted from the manufacturers’ data sheets and bulletins.

What is the ATEX equivalent in the US?The combination of OSHA’s 1910.307 and the NEC classification it refers to, with a laboratory listing in place of a directive. 1910.307(c) gives three ways for equipment to be acceptable in a hazardous (classified) location: intrinsically safe ("permitted in any hazardous (classified) location for which it is approved"), approved for the hazardous location (approved for the Class and for the Group of the specific gas, and marked with class, group and operating temperature), or safe for the location (a type and design the employer demonstrates provides protection, with the NEC as the guideline). The Class I Division 1 and Division 2 definitions, and the Class I Zone 0, 1 and 2 definitions, are in 1910.399. The listing marks on a US instrument are those of the laboratory (UL, cULus, CSA, cETLus, QPS) rather than the "CE 0080 II 1G" style of an ATEX mark.
Is ATEX the same as IECEx, and what is the difference between them?No. ATEX is European Union law: a manufacturer selling into the EU must meet the ATEX directive and marks the product with the CE mark, the notified body number and the Ex marking (for example II 1G Ex ia IIC T4 Ga on the Honeywell BW Clip). IECEx is a voluntary international certification scheme that certifies equipment to the IEC 60079 series of standards and issues a certificate of conformity that many countries accept; it is not a law in any of them by itself. The technical content overlaps almost completely because the ATEX harmonized standards are the EN versions of the same IEC 60079 documents, which is why an instrument’s ATEX and IECEx lines read nearly the same: the BW Clip is "II 1G Ex ia IIC T4 Ga" under ATEX and "Ex ia IIC T4 Ga" under IECEx, the ATEX line adding the equipment group and category (II 1G). Neither one is a US approval.
What is Class 1 Div 2, Group C and D?A location classification under the NEC Division system that 1910.307 uses. Class I means flammable gases or vapors; Division 2 means the gas is present only under abnormal conditions (a leak, a failure, a rupture), as opposed to Division 1 where it is present under normal operation or frequently; Groups C and D name which gases: Group D covers the common hydrocarbons (methane, propane, gasoline vapors and the like) and Group C the more easily ignited gases such as ethylene. 1910.307(e) states that equipment approved for a Division 1 location may be installed in a Division 2 location of the same class and group, so a detector marked Class I, Division 1, Groups A, B, C, D, as the Honeywell BW Clip, MicroClip, MAX XT II and the MSA ALTAIR units are, is listed for a Division 2, Group C or D area too. The same paragraph allows general-purpose equipment in Division 2 only where the employer can demonstrate it is not a source of ignition under normal operating conditions.
Is C1D2 explosion-proof, and what is a Class I Division 2 enclosure?Not necessarily. Explosion-proof is one protection technique, and 1910.307(f)(1) permits it in Class I Division 1 and 2 locations; but Division 2 also accepts nonincendive circuits, nonincendive equipment and components, hermetically sealed equipment and oil-immersed contacts ((f)(5) to (9)), which are lighter forms of protection that would not be accepted in Division 1. So a "Class I Division 2 enclosure" or a Division 2 motor is not automatically an explosion-proof one; it may be a nonincendive or sealed design listed for Division 2 only. A portable gas detector is a different case again: it is listed intrinsically safe, which (c)(1) permits in any location for which it is approved, and intrinsic safety is not explosion-proof construction at all. The zones-and-divisions guide linked below goes through explosion-proof against intrinsically safe in detail.
What are the different types of explosion protection?1910.307 lists them twice. For the Division system, paragraph (f): explosionproof apparatus (Class I Division 1 and 2), dust ignitionproof (Class II), dust-tight (Class II Division 2 and Class III), purged and pressurized (any location for which approved), nonincendive circuit, equipment and component (Division 2), oil immersion (current-interrupting contacts, Class I Division 2), hermetically sealed (Division 2), and any other technique that meets paragraph (c). For the Zone system, paragraph (g)(3): flameproof "d" (Zone 1), purged and pressurized (Zone 1 or 2), intrinsic safety (Zone 0 or 1), type of protection "n" (Zone 2; subdivided nA, nC and nR), oil immersion "o" (Zone 1), increased safety "e" (Zone 1), encapsulation "m" (Zone 1) and powder filling "q" (Zone 1). The IEC scheme adds the letters a, b and c after the technique for the level of protection, which is how a label reads "Ex ia" (intrinsic safety, protection level a, suitable for Zone 0) or "Ex da" (flameproof at level a). The MSA ALTAIR 4XR prints both: "II 1G Ex ia da IIC T3 Ga".
What is ATEX Category 2, and what are Zone 1 and Zone 2 areas?In the ATEX marking the equipment group and category come first: "II" is equipment for places other than mines (group I is mining), and the category is the level of protection, 1 for Zone 0 (gas present continuously or for long periods), 2 for Zone 1 (likely in normal operation), 3 for Zone 2 (not likely, and short-lived if it occurs); the G means gas and D dust. So "II 2G" is Category 2 gas equipment for Zone 1, and the "II 1G" on the Honeywell BW Clip, Solo, Clip4 and MicroClip and the MSA ALTAIR 4XR is Category 1, the highest, for Zone 0. 1910.307(g) carries the same three zones into US law as an alternative to divisions, and (g)(5)(i) states that equipment listed for Zone 0 may be installed in Zone 1 or 2 of the same gas, and Zone 1 equipment in Zone 2. Zones 20, 21 and 22 are the dust equivalents, outside this page.
How do I read the approval line on a Honeywell BW or MSA gas detector?Take the BW Clip datasheet line: "cULus: Class I, Div. 1, Gr. A, B, C, D. Class I, Zone 0, Gr. IIC; ATEX: II 1G Ex ia IIC T4 Ga; IECEx: Ex ia IIC T4 Ga". The first part is the US and Canadian listing by UL (c and us): Class I (gases), Division 1 (gas present in normal operation), Groups A through D (acetylene, hydrogen, ethylene and the hydrocarbon group, every gas group there is), and the Zone equivalent, Class I Zone 0 Group IIC. The ATEX part: II (surface industry), 1G (Category 1, gas, Zone 0), Ex ia (intrinsically safe, level a), IIC (gas group, the most easily ignited, which covers IIA and IIB), T4 (surface temperature class, 135 °C), Ga (equipment protection level, gas, very high). The IECEx line drops the group and category because the scheme uses the EPL (Ga) for that. 1910.307(g)(5)(ii) requires the US zone marking in this order: Class, Zone, "AEx", protection technique, gas group, temperature class, and gives "Class I, Zone 0, AEx ia IIC T6" as its example; the MSA ALTAIR io 4 sheet prints exactly that form, "Class I, Zone 0, AEx da ia IIC Ga T4".
Why does the MSA ALTAIR 4XR say T3 and the BW Clip T4?The temperature class is the maximum surface temperature the equipment can reach in the 40 °C reference ambient, and it must not exceed the ignition temperature of the gas: T1 is 450 °C, T2 300, T3 200, T4 135, T5 100, T6 85. A T4 instrument may be used where a T3 one may and also where gases with ignition temperatures between 135 and 200 °C are present. MSA prints T3 with a −40 °C to +60 °C ambient on the ALTAIR 4XR; Honeywell BW prints T4 on the Clip, Clip4, Solo and MicroClip. 1910.307(c)(2)(ii) is the US rule behind the marking: equipment shall be marked with the class, group and operating temperature or range, and the marking may not exceed the ignition temperature of the gas to be encountered.
Is ATEX accepted in the USA, and is ATEX certification mandatory?An ATEX mark on its own is not a US approval: OSHA’s rule asks for equipment that is approved, which in OSHA’s definitions means acceptable to a nationally recognized testing laboratory. That is why a Honeywell BW or MSA instrument sold here carries the UL, CSA or ETL listing beside its ATEX and IECEx marks, and why a European instrument with only an ATEX mark needs a North American listing before it can be relied on under 1910.307. ATEX is mandatory for equipment placed on the EU market for use in potentially explosive atmospheres; it has no legal force in the United States, and a US buyer needs it only if the instrument will also work in the EU or where a client specification calls for it.
What are intrinsically safe devices, and what is intrinsically safe wiring?Intrinsically safe equipment is designed so that the energy in its circuits, under normal and fault conditions, is too low to ignite the gas it is listed for; 1910.307(c)(1) permits it in any hazardous location for which it is approved, and in the Zone system (g)(3)(iii) permits intrinsic safety in Zone 0 and Zone 1. A portable gas detector is the everyday example: the BW Clip and MicroClip, the MSA ALTAIR line and the RKI units on the sister guide are all listed intrinsically safe. Intrinsically safe wiring is the field wiring of a fixed intrinsically safe system (a sensor head in the hazardous area fed through a barrier in the safe area), covered by NEC Article 504 and by the control drawing that comes with the barrier; it does not arise with a battery-powered portable. The hazardous-location guide linked below covers barriers and systems.
What are the NEC codes for hazardous locations?NFPA 70, the National Electrical Code, which 1910.307 names in its notes: Article 500 (the Class and Division system and the groups), Articles 501 to 503 (Class I, II and III installations), Article 504 (intrinsically safe systems), Article 505 (Class I Zone 0, 1 and 2) and Article 506 (Zone 20, 21 and 22 for dusts). OSHA does not reproduce the NEC; it sets the performance rule and refers to the code for the type and design of equipment that meets it ((c)(3) and the note to (g)(5)).
What is an explosion-proof receptacle, and what metals are explosion-proof?An explosion-proof receptacle is a plug-and-socket assembly in an enclosure built to the explosionproof technique: it can contain an internal explosion of the listed gas and cool the escaping gases below ignition temperature, usually with an interlock so the plug cannot be withdrawn under load. No metal is explosion-proof by itself; the property belongs to the enclosure design, its flame paths and its listing, which is why cast aluminum, iron and steel enclosures are all sold with the mark. Portable gas detectors are not explosion-proof enclosures; they are intrinsically safe instruments, a different technique.
What are the ATEX inspection requirements, and what changed in 2026?ATEX inspection and maintenance in the EU follow EN 60079-17 (inspection and maintenance of installations), with initial, periodic and sample inspections at grades set by the site; the United States has no ATEX inspection requirement, and the equivalent duty here is the employer’s under 1910.307(b) (documentation of classified areas) and the general requirement to maintain equipment to its listing. We do not track changes to the ATEX guidelines; the eCFR shows no change to 1910.307 after January 3 2017, and the instruments in the band carry the markings as the manufacturers print them today.

The three systems in plain words

  • United States: OSHA 1910.307 plus the NEC. Locations are Class I, II or III and Division 1 or 2 (or Class I Zone 0, 1, 2); equipment is listed by a laboratory and marked with class, group and temperature.
  • European Union: the ATEX directive. Equipment is marked CE, the notified body number, the group and category (II 1G, II 2G, II 3G) and the Ex code.
  • International: IECEx, a certification scheme to IEC 60079, with a certificate of conformity and the same Ex code without the ATEX group and category.
  • Division 1 equipment may be used in Division 2 of the same class and group; Zone 0 equipment may be used in Zone 1 and 2 of the same gas (1910.307(e) and (g)(5)(i)).
  • Ex ia is intrinsic safety at the highest level (Zone 0); Ex d is flameproof, the Zone-system name for explosion-proof; e, p, n, m, o and q are the other techniques 1910.307(g)(3) lists.
  • IIC is the gas group that covers hydrogen and acetylene and therefore every lower group; T4 means a 135 °C surface limit, T3 200 °C.
  • A detector sold in the US carries the US listing beside its ATEX and IECEx marks; read the label on the unit you buy, because markings differ by configuration.
29 CFR 1910.307 (c), (e), (f) and (g), current eCFR; manufacturer data sheets as named in the byline.

Questions people ask

What is the ATEX equivalent in the USA?

OSHA’s 29 CFR 1910.307 with the NEC Class, Division and Group (or Class I Zone) system and an NRTL listing such as UL or CSA; there is no US directive, so an instrument sold here carries the US listing beside its ATEX and IECEx marks.

Is ATEX the same as IECEx?

No. ATEX is EU law with a CE mark and category; IECEx is a voluntary international certificate to the IEC 60079 standards. The Ex codes read nearly the same because both use IEC 60079.

What is class 1 div 2 group C and D?

A Class I (gas) location where the gas is present only under abnormal conditions, for Group C (ethylene-type) and Group D (hydrocarbon) gases; Division 1 equipment of the same class and group may be used there under 1910.307(e).

Is C1D2 explosion-proof?

Not necessarily: Division 2 accepts explosion-proof but also nonincendive, hermetically sealed and oil-immersed designs that Division 1 does not; a portable detector is intrinsically safe, a different technique again.

What are the different types of explosion protection?

Under 1910.307: explosionproof, dust ignitionproof, dust-tight, purged and pressurized, nonincendive, oil immersion and hermetically sealed for the Division system; flameproof d, pressurized p, intrinsic safety i, type n, oil o, increased safety e, encapsulation m and powder filling q for the Zone system.

What is the definition of ATEX Category 2?

Equipment for Zone 1, where an explosive gas atmosphere is likely in normal operation; Category 1 is for Zone 0 and Category 3 for Zone 2. The Honeywell BW and MSA portables in the band are Category 1 (II 1G).

What is the full name of ATEX?

From the French "ATmosphères EXplosibles": the EU directives 2014/34/EU (equipment) and 1999/92/EC (workplace protection).

What does the acronym IECEx stand for?

The International Electrotechnical Commission System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres.

Is ATEX certification mandatory?

In the European Union, yes, for equipment placed on the market for use in potentially explosive atmospheres; it has no legal standing in the United States.

What is a Zone 2 hazardous area?

A Class I area where a flammable gas atmosphere is not likely in normal operation and, if it occurs, exists only briefly; 1910.307(g) allows the zone system as an alternative to divisions, and Zone 2 may abut but not overlap Division 2.

What are the NEC codes for hazardous locations?

NFPA 70 Articles 500 to 506: 500 for classes, divisions and groups, 504 for intrinsically safe systems, 505 for Class I zones, 506 for dust zones.

What is intrinsic safe wiring?

The field wiring of a fixed intrinsically safe system through a barrier, per NEC Article 504 and the barrier’s control drawing; a battery-powered portable detector has none.

What are intrinsically safe devices?

Equipment whose circuits cannot release enough energy to ignite the listed gas even under fault; 1910.307(c)(1) permits them in any hazardous location for which they are approved. The gas detectors in the band are examples.

What is the difference between C1D1 and C1D2?

Division 1: the gas is present under normal operation or frequently; Division 2: only under abnormal conditions. Division 1 equipment is accepted in Division 2 of the same class and group.

Does an ATEX mark make a detector legal in a US refinery?

Not on its own; the site’s electrical classification is under 1910.307 and the NEC, which look for an NRTL listing. Honeywell BW and MSA print the UL or CSA listing beside the ATEX mark for that reason.

What is the American equivalent of the ATEX "II 1G" category?

The closest is Class I, Division 1 (or Class I, Zone 0 under the US zone marking "AEx"); the Honeywell BW Clip prints Class I, Division 1 and Class I, Zone 0 Group IIC beside its II 1G ATEX line.

Related guides

ATEX vs explosion-proof vs intrinsically safeZones, divisions and the marks on a gas detectorWhat is a hazardous (classified) location?Class, division, group and intrinsic safetyIntrinsically safe gas detectorsWhat Class I Div 1 and Div 2 mean on the labelHow to calibrate, bump test and reset an MSA ALTAIR 4XRButtons, zero and span, the LEDs and the 4X differencesHow to bump test, zero and turn off a Honeywell BW ClipActivation, hibernation and the end-of-life countdownWho owns BW Technologies, Honeywell Analytics and MSA?What each company makes, in its own words

The ratings, test results and standards shown here are the manufacturers' published values, reproduced as published. Nothing on this page is a recommendation by Bayshore Safety that any product is suitable for a particular task, hazard or workplace. Selecting safety products and protective equipment is the responsibility of the end user and the employer, based on their own hazard assessment and the regulations that apply to their work. Confirm every value on the manufacturer's own documentation before use.

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