Class 1, Division 1 electrical requirements are part of the National Electrical Code (NEC) and apply to environments where flammable gases, vapors, or liquids are present under normal operating conditions or are frequently released due to equipment operation or maintenance.

What Are Class 1, Division 1 Environments?

Class 1, Division 1 (C1D1) areas involve constant or intermittent presence of flammable substances. These conditions make ignition highly likely if equipment or safety protocols fail. Typical examples include:

• Oil and gas facilities: Refineries, drilling sites, and pipeline operations.
• Chemical Plants: Areas that handle volatile chemicals regularly.
• Mining Operations: Zones with naturally occurring explosive gases.

Unlike Division 2 locations, where hazardous substances are only present during abnormal conditions, Division 1 environments require the highest level of protection at all times.

How Does Class 1, Division 1 Differ from Division 2?

The main difference between Class 1, Division 1, and Division 2 environments lies in the frequency and presence of hazardous substances. Class 1, Division 1 environments involve the constant or frequent presence of flammable gases, vapors, or liquids during normal operations, demanding the use of explosion-proof and intrinsically safe equipment.

In contrast, Class 1, Division 2 environments encounter hazardous substances only under abnormal conditions, such as equipment malfunctions or accidental leaks. As a result, Division 2 requirements are less stringent, allowing the use of certain industrial-grade equipment not permissible in Division 1.

Sealing and wiring requirements also differ. Division 1 requires stringent sealing and explosion-proof conduit systems to prevent gas migration, while Division 2 permits moderate sealing measures due to the lower likelihood of continuous exposure to flammable substances.

Key Electrical Requirements for Class 1, Division 1

• All equipment must be capable of containing explosions to prevent ignition of surrounding flammable atmospheres.
• Electrical circuits must operate with limited energy to ensure they cannot ignite hazardous substances, even during faults.
• Equipment housings must prevent gas ingress and be designed for continuous safety in volatile conditions.

Wiring methods

Wiring in Class 1, Division 1 areas must prevent sparks, heat, or gas migration. The approved methods include:

• Rigid Metal Conduit (RMC):
• Provides maximum protection for conductors. Sealing fittings must be installed at key points, such as within 18 inches of enclosures, to contain gases.
• Mineral-Insulated (MI) Cable:
• MI cables offer excellent fire and mechanical resistance, featuring a gas-tight copper sheath for maximum safety.
• MC-HL (Metal-Clad Hazardous Location) Cables:
• MC-HL cables are designed with continuous gas-tight sheathing and armor.
• Explosion-Proof Flexible Conduits:
• Used for equipment requiring movement or vibration, ensuring safety without compromising flexibility.

Sealing requirements

Sealing systems are crucial to prevent gas migration through conduits:

Boundary seals

Installed transitions between Division 1 and unclassified or Division 2 areas.

Conduit seals

Mandatory to within 18 inches of enclosures to isolate hazardous areas.

Bonding and grounding

Proper bonding and grounding prevent static discharge, a potential ignition source:

Conduits and cable trays

All metallic systems must be bonded and grounded for electrical continuity.

Equipment grounding

Enclosures, control panels, and other metallic structures must be securely grounded.