Pressure Switch Classes, Divisions, Groups
Classes ExplainedCLASS: According to the National Electric Code (NEC) there are three types of hazardous locations:
Class I:The first type of hazard is one which is created by the presence of flammable gasses or vapors in the air, such as natural gas or gasoline vapor. When these materials are found in the atmosphere, a potential for explosion exists, which could be ignited if an electrical or another source of ignition is present. Some typical Class I locations are:
- Petroleum refineries, gasoline storage, and dispensing areas
- Dry cleaning plants where vapors from cleaning fluids can be present
- Spray finishing areas
- Aircraft hangars and fuel servicing areas
- Utility gas plants and operations involving storage and handling of liquefied petroleum gas or natural gas
Class II:Class II hazard areas are made hazardous by the presence of combustible dust. A finely pulverized material, suspended in the atmosphere, can cause as powerful an explosion as one occurring at a petroleum refinery. Some typical Class II locations are:
• Grain elevators
• Flour and feed mills
• Plants that manufacture, use or store magnesium or aluminum powders
• Producers of plastics, medicines, and fireworks
• Producers of starch or candies
• Spice grinding plants, sugar plants, cocoa plants
• Coal preparation plants and other carbon handling or processing areas
Class III:Class III hazardous locations are areas where there are easily-ignitable fibers or flyings present, due to types of materials being handled, stored, or processed. The fibers and flyings are not likely to be suspended in the air but can collect around machinery or on lighting fixtures and where heat, a spark, or hot metal can ignite them. Some typical Class III locations are:
• Textile mills, cotton gins
• Cottonseed mills, flax processing plants
• Plants that shape, pulverize, or cut wood and create sawdust of flyings
Divisions ExplainedDIVISION: The condition in which the hazardous material exists.
Division 1: Normal conditionsDivision 1 locations occur where hazardous concentrations of flammable gases or vapors exist continuously, intermittently, or periodically under normal conditions. Under normal conditions, the hazard would be expected to be present in everyday production operations or during frequent repair and maintenance activity.
Division 2: Abnormal conditionsDivision 2 hazardous locations occur where flammable volatile liquid or flammable gasses are handled, processed, or used, but in which they will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture, breakage, unusual faulty operation; causing an abnormal situation.
Groups ExplainedGROUPS: The hazardous substance/material. Materials are grouped according to the ignition temperature of the substance, its explosion pressure, and other flammable characteristics.
Group A:There is only one substance in Group A, which is acetylene. Acetylene is a gas with extremely high explosion pressures.
Group B:This group is a relatively small segment of classified areas. This group includes hydrogen and other materials with similar characteristics like fuel and combustible process gasses containing more than 30% hydrogen by volume or gasses of equivalent hazard such as butadiene, ethylene, oxide, propylene oxide and acrolein.
Groups C and D:comprise the greatest percentage of all Class I hazardous locations.
Group C: Some of the many substances in Group C include: carbon monoxide, ether, hydrogen sulfide, morphline, cyclopropane, ethyl and ethylene, or gasses of equivalent hazard.
Group D: Some of the many substances in Group D include: gasoline, acetone, ammonia, benzene, butane, cyclopropane, ethanol, hexane, methanol, methane, vinyl chloride, natural gas, naphtha, propane or gasses of equivalent hazard.