The National Electric Code (NEC) or NFPA 70 defines hazardous locations as those areas where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. This article will focus on hazardous areas where flammable liquids exist. There are three types of Classes. Class 1 locations are created by the presence of flammable vapors or gases that are in the air in sufficient quantities to be explosive or ignitable. When these materials are found in the atmosphere, a potential for explosion exists if an electrical or other source of ignition is present.
Risk Logic advises on process hazard reviews. Contact Risk Logic with any questions you may have regarding property loss prevention for flammable liquid operations.
Sources of ignition can create a hazardous location. Typically there are three causes of ignition:
- Arcs and sparks produced by the normal operation of equipment (i.e. motor starters, contactors, and switches)
- The high temperatures of some heat-producing equipment (i.e. lamps and lighting fixtures)
- Electrical equipment failure (i.e. shorting of a terminal)
NFPA establishes area classifications based on Classes, Divisions and Zones. Classes and Divisions are the most popular. The Occupational Safety and Health Administration (OSHA) has adopted these hazardous classifications from the NEC and they are defined in 29 Code of Federal Register (CFR) 1910.399.
Definition of Hazardous Locations
Class I, Division 1: There are three different situations that could exist to classify an area as a Class I, Division 1 location:
- Ignitable concentrations of flammable gases or vapors may exist under normal operating conditions.
- Ignitable concentrations of such 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 simultaneous failure of electric equipment.
Class I, Division 2: One of the following three situations must exist in order for an area to be considered a Class I, Division 2 location:
- Volatile flammable liquids or flammable gases are handled, processed or used, but the hazardous liquids, vapors or gases will normally be confined within closed containers or closed systems from which they can escape only in the event of accidental rupture or breakdown of such containers or systems, or as a result of abnormal operation of equipment.
- Ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operations of the ventilating equipment.
- Adjacent to a Class I, Division 1 location, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.
There are three categories based on volume of flammable liquid in a container where Class I Division 1 or 2 are defined:
- Less than < 5 gallons in a single container does not require rated electrical equipment as this is a limited exposure
- Between 5 gallons and 70 gallons in an open or closed container
- Greater than > 70 gallons in an open or closed container
The above tables and diagrams are provided in FM Global Data Sheet 7-32, Ignitable Liquid Operations.
Electrical equipment can be purchased for hazardous locations Class I Division 1 or Class I Division 2. Equipment for Class I Division 1 are more secure than Division 2 and can be located in the Division 2 area as well.
Risk Logic can provide a hazard review assessment. Please contact us with any questions you may have regarding flammable liquid operations.