Hazardous Locations: Classes, Divisions & Zones

Q: Why is hazardous area classification required?

Hazardous area classification under the National Electrical Code supports safe equipment selection, regulatory compliance, and consistent documentation. Hazardous area classification guides are also beneficial during facility planning, design, and development to help reduce risk and improve safety standards.

Q: How do I determine the correct classification for a facility?

Determining the correct classification requires a formal assessment of materials handled, operational processes, ventilation conditions, and potential failure scenarios. The evaluation defines whether the Class/Division or Zone system applies and confirms the appropriate hazardous area zones for the facility.

The Importance of NEC Hazardous Location Classification

NEC hazardous location classification identifies the material type and how often it may be present. This information supports equipment approval, inspections, and safe operation. It also aligns with explosive atmosphere classification, giving workers a clear understanding of the explosion risk in the area.

How the Class and Division System Works

The Class and Division system groups hazards by material type and exposure frequency. It is the foundation of hazardous location classes and divisions used across many industries.

Hazard classes are by material type:

Class I classification applies to flammable gases or vapors.

Class II classification applies to combustible dusts.

Class III classification applies to ignitable fibers or flyings.

Divisions are based on likelihood of exposure:

Division 1 applies where a hazardous material is present during normal operation.

Division 2 applies where a hazardous material is not normally present and appears only under abnormal conditions.

These can then be combined to form a broader picture. For example, Class I Division 1 indicates a flammable gas or vapor that is expected to be present during normal operation. Class II Division 2, on the other hand, indicates a combustible dust that is not expected to be present in normal conditions.

How the Zone System Classifies Risk Levels

The Zone system classifies hazardous areas based on how often an explosive atmosphere is present. It separates gas, vapor, and dust hazards and is widely used outside North America.

Zones 0 to 2 are used to classify gas or vapor hazards.

Zone 0, Zone 1, and Zone 2 differences:

Zone 0: Flammable gas or vapor is present continuously or for long periods.
Zone 1: Gas or vapor is likely during normal operation.
Zone 2: Gas or vapor appears only during abnormal conditions.

Zones 20 to 22 follow the same format, but for combustible dust hazards:

Zone 20: Combustible dust is present continuously or for long periods.
Zone 21: Combustible dust is present during normal operation.
Zone 22: Combustible dust is present only under abnormal conditions.

Class/Division vs. Zone System

The table below shows how hazardous location classes and divisions generally align with hazardous area zones for gas and dust hazards.

Class and Division	Typical Hazard Type	Comparable Zone
Class I Division 1	Flammable gas or vapor present during normal operation	Zone 0 or Zone 1
Class I Division 2	Gas or vapor present only under abnormal conditions	Zone 2
Class II Division 1	Combustible dust present during normal operation	Zone 20 or Zone 21
Class II Division 2	Dust present only under abnormal conditions	Zone 21 or Zone 22
Class III	Ignitable fibers or flyings	No direct zone equivalent

Like explosive atmosphere classifications, these zones provide a clear indication of the risks present in an area.

Frequently Asked Questions

What is the difference between Class I and Zone 0 classifications?

Class I identifies the type of hazard present, specifically flammable gases or vapors. Zone 0 defines a specific condition where flammable gas or vapor is present continuously or for long periods during normal operation. One describes the material, while the other describes the nature of the exposure.

Why is hazardous area classification required?

NEC hazardous location classification supports safe equipment selection, regulatory compliance, and consistent documentation. Hazardous area classification guides can also be beneficial during facility planning and development.

How do I determine the correct classification for a facility?

A formal assessment must be done to review materials, processes, ventilation, and failure conditions. The result defines the correct Class/Division vs. Zone system and confirms hazardous area zones.