What Is Class 1 Division 2?

Class 1 Division 2, usually written Class I, Division 2 in the codes and C1D2 for short, is a hazardous location rating used in the United States and Canada. Class I means flammable gases or vapours may be present. Division 2 means they are not expected in normal operation, and would only appear under abnormal conditions such as a leak, a failed seal or a ventilation fault.

The system comes from the US National Electrical Code (NEC), Article 500 onwards, and the Canadian Electrical Code. Equipment rated for Class I, Division 2 will not ignite the surrounding atmosphere in normal operation. It is the most common hazardous location rating for computers, HMIs and displays, because it covers the large areas around process plant rather than the inside of tanks and vents.

A full hazardous location rating has three parts: the class (what kind of material), the division (how likely it is to be present) and the group (which specific material).

The division is the part buyers most often get wrong, and it decides how the equipment must be protected.

Equipment rated for Division 1 can be used in Division 2, but not the other way round. Many Division 2 products are also rated for groups A to D and a specific T code, which should appear on the nameplate alongside the class and division.

Class I, Division 1 is the stricter of the two gas divisions. Under NEC Article 500 it covers locations where ignitable concentrations of flammable gas or vapor exist under normal operating conditions, exist often because of repair, maintenance or leakage, or could be released by a breakdown that also causes an electrical fault. Typical examples are the inside of spray booths, the area around open dip tanks and filling points, and pits or sumps where heavy vapours collect.

Because the hazard is expected rather than occasional, Division 1 equipment must stay safe even if the atmosphere is present while it runs. That rules out the nonincendive designs used in Division 2 and leaves three main methods:

Full computers rarely go into Division 1. The usual design keeps the computer in a Division 2 or unclassified area and brings the field signals to it through intrinsically safe barriers, or houses it in a purged cabinet. Division 2 is where most hazardous location computers, displays and network switches are listed, and that is the area our catalog covers.

Our rugged tablets include a 10.1 inch model listed for Class I, Division 2, Groups A, B, C and D, T4, alongside ATEX and IECEx Zone 2, and several of our managed industrial switches list UL Class 1 Division 2 approval for control cabinets in classified areas. None of these are rated for Division 1.

In the US, hazardous location equipment is tested and listed by a Nationally Recognized Testing Laboratory (NRTL) such as UL, CSA, FM Approvals or Intertek. For computers and HMIs, the usual standard for Division 2 is UL 121201 (formerly ISA 12.12.01), which covers nonincendive electrical equipment. In Canada, the equivalent is CSA C22.2 No. 213.

The listing appears on the nameplate, for example “Class I, Division 2, Groups A, B, C, D, T4”. Our guide to UL listed computers for control panel builders explains how listings work more generally.

A Division 2 listing is the starting point, not the whole specification. Check these points against the area classification drawing before ordering.

Europe and much of the rest of the world use zones under ATEX and IECEx rather than divisions. Division 1 covers what the zone system splits into Zone 0 and Zone 1, while Division 2 broadly matches Zone 2. Our ATEX zones explainer sets out each zone.

Our hazardous area panel PCs include Class I, Division 2 HMI panel PCs, and the wastewater HMI case study shows a C1D2 HMI in use. We integrate and validate each system as standard, keeping within the listed configuration.