Classifications

Hazardous or classified locations are assigned specific designations and classified into categories based on properties of the materials present, such as:

• Flammable vapors, liquids, or gases
• Combustible dusts or fibers that may be present
• Likelihood there is a flammable or combustible concentration or quantity present

Class I, Division 1 refers to a location in which one of the following conditions exists:

• Ignitable concentrations of flammable gases or vapors may exist under normal operating conditions.
• Ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage.
• Breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors and might also cause electrical equipment to fail.

Class I, Division 2 refers to a location in which one of the following conditions exists:

• Volatile flammable liquids or flammable gases are handled, processed, or used but will normally be confined within closed containers or closed systems.
• Ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation equipment.
• The location is adjacent to a Class I, Division 1 location, where ignitable concentrations of gases or vapors might occasionally be present.

Class II, Division 1 refers to a location in which one of the following conditions exists:

• Combustible dust is or may be in suspension in the air under normal operating conditions in quantities sufficient to produce explosive or ignitable mixtures.
• A mechanical failure or abnormal operation of machinery or equipment might cause explosive or ignitable mixtures to be produced, and might also provide a source of ignition.
• Combustible dusts of an electrically conductive nature may be present.

Class II, Division 2 refers to a location in which both of the following conditions exists:

• Combustible dust may be in suspension in the air because of infrequent malfunctioning equipment.
• Combustible dust accumulations on, in, or near the electrical equipment may be sufficient to interfere with the safe dissipation of heat from electrical equipment or may be ignitable by the abnormal operation or failure of electrical equipment.

Class III, Division 1 refers to a location in which easily ignitable fibers or materials that produce combustible particles are handled, manufactured, or used.

Class III, Division 2 refers to a location in which easily ignitable fibers are stored or handled, other than in the process of manufacture.

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