Intrinsically Safe Knowledge Base
Class II Division 1 vs Division 2: Combustible Dust Ratings
Class II Division 1 and Class II Division 2 are the two levels the US hazardous-location rules use for combustible dust. The difference is how likely dust is to be in the air, in what quantity, and under which conditions. In a Division 1 location, combustible dust is or may be in suspension in the air under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures. In a Division 2 location, dust is not normally in suspension in those quantities; it gets there only through the infrequent malfunctioning of handling or processing equipment (29 CFR 1910.399).
Class II covers dust only. Gases and vapors fall under Class I. In OSHA’s rule for hazardous (classified) locations, Class II installations are classified with the division system, not the zone system (29 CFR 1910.307(a)(4)), and equipment must be approved for the class of location and for the specific dust that will be present (29 CFR 1910.307(c)(2)(i)). This guide compares the two divisions, shows where each one applies, and explains what changes when you select equipment.
Class II Division 1 vs Division 2: Side by Side
| Class II, Division 1 | Class II, Division 2 | |
|---|---|---|
| Hazard | Combustible dust | Combustible dust |
| Dust in the air | Is or may be in suspension under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures | Will not normally be in suspension in such quantities; may be in suspension because of infrequent malfunctioning of handling or processing equipment |
| Equipment failure | Mechanical failure or abnormal operation might produce explosive or ignitable mixtures and also provide a source of ignition through simultaneous failure of electric equipment | Dust accumulations on, in or near electric equipment may interfere with safe dissipation of heat, or may be ignitable by abnormal operation or failure of electric equipment |
| Conductive dusts | Division 1 if present | — |
| Dust-ignitionproof equipment | Permitted for Class II, Division 1 and 2 | Permitted for Class II, Division 1 and 2 |
| Dust-tight equipment | Listed for Division 2 and Class III only | Permitted for the locations it is approved for (Division 2 and Class III) |
| Nonincendive circuit, equipment or component; hermetically sealed | Listed for Division 2 only (and Class III) | Permitted for the locations they are approved for |
Sources: 29 CFR 1910.399 (definitions) and 29 CFR 1910.307(f)(2), (3), (5) to (7) and (9) (protection techniques).
Where Each Division Applies
OSHA’s definitions include explanatory notes with examples.
Division 1. The note says this classification may include grain handling and processing plants, starch plants, sugar-pulverizing plants, malting plants, hay-grinding plants, coal pulverizing plants, areas where metal dusts and powders are produced or processed, and similar locations that contain dust-producing machinery and equipment, except where the equipment is dust-tight or vented to the outside (29 CFR 1910.399).
Division 2. The note says this classification includes locations where dangerous concentrations of suspended dust would not be likely, but where dust accumulations might form on or near electric equipment. These areas may contain equipment from which appreciable quantities of dust would escape under abnormal operating conditions, or may be adjacent to a Class II Division 1 location (29 CFR 1910.399).
Which dusts? OSHA’s note lists examples of electrically nonconductive combustible dusts: grain and grain products, pulverized sugar and cocoa, dried egg and milk powders, pulverized spices, starch and pastes, potato and wood flour, oil meal from beans and seed, and dried hay. It adds that dusts containing magnesium or aluminum are particularly hazardous (29 CFR 1910.399).
Class II vs Class I: Dust vs Gas
Class I locations are those hazardous because of flammable gases, vapors or liquids; Class II locations are those hazardous because of combustible dust (29 CFR 1910.399). The division numbers follow the same idea in both classes: Division 1 is the level where the hazard can be present under normal operating conditions, Division 2 the level where it is not normally present. For the gas side of the comparison, see our guide to Class 1 Division 1 vs Division 2. For a definition of the higher dust level on its own, see What is a Class 2 Division 1 hazardous location.
Equipment approved for Class I is not automatically approved for Class II: OSHA requires approval for the class of location and for the specific gas, vapor, dust or fiber that will be present (29 CFR 1910.307(c)(2)(i)).
What It Means for Equipment Selection
- Approval for the class and the dust. Equipment must be approved not only for the class of location but also for the ignitable or combustible properties of the specific dust (29 CFR 1910.307(c)(2)(i)). OSHA notes that NFPA 70, the National Electrical Code, lists or defines hazardous gases, vapors and dusts by “Groups”.
- Marking. Equipment is marked to show the class, group and operating temperature or temperature range, based on operation in a 40-degree C ambient (29 CFR 1910.307(c)(2)(ii)). Fixed dust-tight equipment, other than lighting fixtures, that is acceptable for Class II Division 2 and Class III locations need not be marked with the class, group, division or operating temperature (29 CFR 1910.307(c)(2)(ii)(D)).
- Division 1 equipment in a Division 2 location. Equipment approved for a Division 1 location may be installed in a Division 2 location of the same class and group (29 CFR 1910.307(e)).
- Intrinsic safety. Equipment and associated wiring approved as intrinsically safe is permitted in any hazardous location for which it is approved (29 CFR 1910.307(c)(1)).
- Documentation. Areas designated as hazardous (classified) locations must be properly documented, and the documentation must be available to those authorized to design, install, inspect, maintain or operate electric equipment at the location (29 CFR 1910.307(b)).
How to Read a Class II Rating on a Product Page
Product pages state the rating in different forms. These examples are copied from the listings (checked on 2026-10-14):
Prestivac EX1-5 Hepa Explosion Proof Vacuum
“Class I, Division 1, Group D and Class II, Division 1, Groups E, F, and G Hazardous Locations as defined in the National Electric Code (NEC) and NFPA 70”
— product page
Prestivac EV1-10 EX RCT Explosion Proof Vacuum
“Features: Class II Division 2” and “…which is classified as Class II Division 2”
— product page
Both are in stock at the time of writing. The first states Division 1 with Groups E, F and G; the second states Division 2. Read the rating on each listing, because the same product family can be rated for different divisions and groups.
For lighting, browse the Class 2 Division 1 portable lighting category. Each listing states its own class, division and group rating.
How to Choose Between Division 1 and Division 2 Equipment
- Find the classification documentation for the area. It should state Class II and the division (29 CFR 1910.307(b)).
- Identify the dust and its group. Equipment must be approved for the specific dust (29 CFR 1910.307(c)(2)(i)).
- Match the marking. Check class, group and operating temperature on the equipment (29 CFR 1910.307(c)(2)(ii)).
- Check the protection technique. Dust-tight and nonincendive equipment are listed for Division 2, while dust-ignitionproof equipment is listed for both divisions (29 CFR 1910.307(f)). For the IEC 60079 side of dust ignition protection, see dust ignition testing standards explained.
- Check which division the equipment is approved for. OSHA’s text describes equipment approved for a Division 1 location as installable in a Division 2 location of the same class and group (29 CFR 1910.307(e)); it does not describe Division 2-only equipment as installable in Division 1.
FAQ
What is the difference between Class II Division 1 and Division 2?
Division 1 is where combustible dust is or may be in suspension under normal operating conditions, or where equipment failure might both produce an ignitable mixture and ignite it, or where conductive dusts may be present. Division 2 is where dust is not normally in suspension in such quantities and only gets there through infrequent malfunctions, but accumulations may interfere with heat dissipation or be ignitable (29 CFR 1910.399).
Is Division 1 or Division 2 more hazardous?
Division 1 is considered more hazardous because the combustible dust is, or may be, in suspension under normal operating conditions. In Division 2, dust is not normally in suspension in such quantities and gets there only through infrequent malfunctioning of handling or processing equipment, making the risk less frequent (29 CFR 1910.399).
What is the difference between Class 1 and Class 2 hazardous locations?
Class I is gases, vapors and liquids; Class II is combustible dust (29 CFR 1910.399).
Does ATEX have a “Class 2”?
No. “Class II” belongs to the US system. Under the European ATEX rules, places with combustible dust are classified in Zones 20, 21 and 22; for example, Zone 22 is a place where an explosive dust cloud is not likely to occur in normal operation but, if it does occur, will persist for a short period only (Directive 1999/92/EC, Annex I). That zone definition is not a one-to-one translation of Division 2. For how divisions and zones compare on the gas side, see Class I Div 2 vs ATEX Zone 2.
Can Class I Division 1 equipment be used in a Class II Division 1 area?
Only if it is also approved for Class II and for the specific dust. OSHA requires approval for the class of location and for the specific properties of the gas, vapor, dust or fiber present (29 CFR 1910.307(c)(2)(i)).
Can Class II locations be classified with zones in the US?
Under OSHA’s rule, Class II and Class III locations must be classified using the division system. The zone system is an alternative only for Class I locations (29 CFR 1910.307(a)(4)).