A US operator, a European charterer and a Canadian shipyard can all describe the same hazardous area in three different languages. In Europe you hear “Zone 1”. In the United States you hear “Class I, Division 1”. The two systems are related, but they are not interchangeable, and getting it wrong can mean buying equipment that is rejected at inspection.

The short answer: the US traditionally classifies hazardous locations by Class and Division under the National Electrical Code (NEC). ATEX and IECEx use Zones. The US also recognises a Zone system, so equipment can be certified either way. Division 1 roughly corresponds to Zones 0 and 1, and Division 2 roughly corresponds to Zone 2, but the match is approximate.

If you want the zone basics first, start with what ATEX is and how Zones 0, 1 and 2 work.

How the US system works

In the NEC, the hazardous location is described in three steps.

1. Class: what kind of hazard is present

Class Hazard
Class I Flammable gases and vapours
Class II Combustible dust
Class III Ignitable fibres and flyings

2. Division: how likely the hazard is

Division Meaning
Division 1 The hazard is present under normal operating conditions, or often because of repair, maintenance or leakage
Division 2 The hazard is present only under abnormal conditions, such as a leak or equipment failure

3. Group: which substance

For Class I gases, Groups A to D run from the most demanding to the least: A is acetylene, B includes hydrogen, C includes ethylene, and D includes propane, methane and gasoline vapour. Dust groups are E, F and G.

Equipment also carries a temperature code from T1 to T6, the same idea as the T class in ATEX.

The zone system in the US

The NEC also allows a Zone approach for Class I locations (Article 505), and for dust (Article 506). Equipment certified this way is marked AEx and uses the same Zone 0, 1 and 2 logic and the same IIA, IIB and IIC groups as ATEX and IECEx. For offshore oil and gas, API RP 505 is a widely used recommended practice for classifying locations into Zones.

The two US routes mean you might see either of these on a US-approved device:

  • Class I, Division 1, Groups C, D, T4
  • Class I, Zone 1, AEx ib IIC T4 Gb

ATEX zones vs US divisions: the rough mapping

ATEX / IECEx gas group US Class I group
IIC A and B (acetylene, hydrogen)
IIB C (ethylene)
IIA D (propane, methane, gasoline vapour)

The mapping is a guide to thinking, not a conversion chart. A Division 1 area covers both Zone 0 and Zone 1, so a device rated for Zone 1 may not be accepted where a location needs Zone 0 protection. The certificate and the authority having jurisdiction decide, not the table.

Who certifies equipment in the US?

In the US, equipment for hazardous locations is typically certified by a Nationally Recognized Testing Laboratory (NRTL), such as UL, FM Approvals, CSA or Intertek. An ATEX or IECEx certificate on its own does not automatically satisfy a US requirement for a listed product. Equipment can carry several certifications, and that is the practical answer for operators working across regions.

Regulations that commonly come up for marine and offshore work include electrical installation rules for vessels under US Coast Guard regulations (46 CFR Part 111), OSHA workplace rules for hazardous locations (29 CFR 1910.307), and API recommended practices for offshore facilities. The inspector, class society or operator has the final say on what is acceptable on your vessel or installation.

Canada uses a similar approach through the Canadian Electrical Code and CSA certification, with Zone-based marking widely accepted.

What this means when you buy safety equipment

For personal and portable gear carried into classified areas, such as beacons, lights and lifejackets:

  • Start with your classification. Is your location described as Class/Division, as Zones, or both?
  • Ask what certification your inspector, class society or operator will accept. For US-flag vessels and US offshore sites, do not assume an ATEX certificate is enough.
  • For international operations, buy dual-certified equipment where possible. It avoids one fleet for Europe and another for the US.
  • Check the gas group and temperature class against what is on site.

Some of the equipment we supply is certified for hazardous areas under ATEX and IECEx, including the sMRT V300-X1/X2 ATEX/IECEx beacon and the L6 lifejacket light. Others are certified to ATEX Zone 2, like the sMRT AU10X and sMRT AU11X. We also supply SOLAS ATEX lifejackets. If your site requires US-specific listings, ask us for the certification held by each model before you order.

What hazardous-area ratings mean for marine safety equipment

For offshore crews and marine operators, hazardous-area certification can be an important consideration when selecting personal safety equipment for work in potentially explosive atmospheres.

Personal locator beacons and man-overboard locating devices may need to meet specific hazardous-area requirements in addition to their marine safety and performance requirements. The correct choice depends on the area’s classification, the equipment’s certification and the requirements of the relevant operator or approving authority.

Marine Rescue Technologies supplies marine safety equipment for these demanding environments, including the sMRT V300-X1/X2 with ATEX/IECEx certification and the ATEX Zone 2-approved sMRT AU10X and AU11X.

When selecting equipment for operations in the United States, buyers should not assume that an ATEX or IECEx certificate alone establishes acceptance. Confirm the required approval for the intended application and check the current certification documentation for the exact product and model.

MRT can help customers identify the relevant product documentation and understand which questions to confirm with their vessel operator, class society or approving authority before ordering.

You can browse the full range on our ATEX safety equipment page or in the AIS personal locator beacons category. For more on how the two certification schemes differ, read ATEX vs IECEx.

Frequently asked questions

Is Zone 1 the same as Division 1? Not exactly. Division 1 covers both Zone 0 and Zone 1 conditions, so the match is approximate.

Can I use ATEX equipment in the US? Sometimes. It depends on the location, the inspector and whether a US-recognised certification is required. Ask before you buy.

Does the US recognise Zones? Yes. The NEC allows Zone classification for Class I locations, and equipment can be marked AEx.

What is the AEx marking? It is the US marking for equipment certified to the Zone system. It is similar in structure to an ATEX marking.

Which is better, Class/Division or Zones? Neither is better. Zones give finer detail on how often a hazard occurs, and they are used internationally, which is why many offshore operators prefer them.

Not sure what your site requires?

Marine Rescue Technologies is based in Florida and has supplied marine safety equipment for more than 25 years. We offer complimentary consulting to help match certification to your vessel or installation. Contact us with your classification and region and we will help you choose.