What is a Hazardous Location? Know the Classification System

Any jobsite is a potentially hazardous location, but some locations have invisible dangers that present additional risks. OSHA officially classifies and labels these jobsites hazardous locations. They possess the presence—or potential presence—of flammable gases, vapors, liquids, combustible dust, or ignitable fibers and flyings. In the most potentially volatile work areas, it’s critical that equipment is intrinsically safe. This means it’s electrically engineered to avoid igniting an explosion. OSHA’s classification system of hazardous locations consists of classes, divisions, and zones.

The hazardous classification system gets a bit wordy, but it’s critical to know the designation for your jobsite. Although much of the difference in classes, divisions, and zones depends on whether a combustible environment always exists on a jobsite or whether it might exist due to an accident, we’ll avoid paraphrasing to prevent miscommunication. You can find this information under OSHA Standard Number 1910.399.

Hazardous Class I Locations

Class I locations are those in which flammable gases or vapors already exist or may exist in the air in quantities sufficient to produce explosive or ignitable mixtures. Class I locations include the following:

(1) Class I, Division 1

A Class I, Division 1 location is a location:

1. In which ignitable concentrations of flammable gases or vapors may exist under normal operating conditions; or
2. In which ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
3. In which 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.

Note to the definition of “Class I, Division 1:” This classification usually includes locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another. This might also include interiors of spray booths and areas in the vicinity of spraying and painting operations that use volatile flammable solvents. It could also apply to locations containing open tanks or vats of volatile flammable liquids, drying rooms, or compartments for the evaporation of flammable solvents.

Locations containing fat and oil extraction equipment using volatile flammable solvents or portions of cleaning and dyeing plants that use flammable liquids also fall under this designation. It includes gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape as well as inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids.

You also have the interiors of refrigerators and freezers which store volatile flammable materials in open, lightly stoppered, or easily ruptured containers. It also includes all other locations where ignitable concentrations of flammable vapors or gases may occur in the course of normal operations.

(2) Class I, Division 2

A Class I, Division 2 location is a location:

1. In which volatile flammable liquids or flammable gases are handled, processed, or used, but in which 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; or
2. In which 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; or
3. That is 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.

Note to the definition of “Class I, Division 2

This classification usually includes locations where volatile flammable liquids or flammable gases or vapors are used, but which would become hazardous only in case of an accident or of some unusual operating condition. The quantity of flammable material that might escape in case of accident, the adequacy of ventilating equipment, the total area involved, and the record of the industry or business with respect to explosions or fires are all factors that merit consideration in determining the classification and extent of each location.

Piping without valves, checks, meters, and similar devices would not ordinarily introduce a hazardous condition even though used for flammable liquids or gases. Locations used for the storage of flammable liquids or liquefied or compressed gases in sealed containers would not normally be considered hazardous unless also subject to other hazardous conditions.

Electrical conduits and their associated enclosures separated from process fluids by a single seal or barrier are classed as a Division 2 location if the outside of the conduit and enclosures exist in a nonhazardous location.

Class I, Zone 0 Hazardous Zones

A Class I, Zone 0 location is a location in which one of the following conditions exists:

1. Ignitable concentrations of flammable gases or vapors are present continuously; or
2. Ignitable concentrations of flammable gases or vapors are present for long periods of time.

Note to the definition of “Class I, Zone 0:” As a guide in determining when flammable gases or vapors are present continuously or for long periods of time, refer to Recommended Practice for Classification of Locations for Electrical Installations of Petroleum Facilities Classified as Class I, Zone 0, Zone 1 or Zone 2, API RP 505-1997; Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous Areas, IEC 79-10-1995; Area Classification Code for Petroleum Installations, Model Code — Part 15, Institute for Petroleum; and Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous (Classified) Locations, ISA S12.24.01-1997.

Class I, Zone 1

A Class I, Zone 1 location is a location in which one of the following conditions exists:

1. Ignitable concentrations of flammable gases or vapors are likely to exist under normal operating conditions; or
2. Ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or
3. Equipment is operated or processes are carried on of such a nature that equipment breakdown or faulty operations could result in the release of ignitable concentrations of flammable gases or vapors and also cause simultaneous failure of electric equipment in a manner that would cause the electric equipment to become a source of ignition; or
4. A location that is adjacent to a Class I, Zone 0 location from which ignitable concentrations of vapors could be communicated unless the communication is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.

Class I, Zone 2

A Class I, Zone 2 location is a location in which one of the following conditions exists:

1. Ignitable concentrations of flammable gases or vapors are not likely to occur in normal operation and if they do occur will exist only for a short period; or
2. Volatile flammable liquids, flammable gases, or flammable vapors are handled, processed, or used, but in which the liquids, gases, or vapors are normally confined within closed containers or closed systems from which they can escape only as a result of accidental rupture or breakdown of the containers or system or as the result of the abnormal operation of the equipment with which the liquids or gases are handled, processed, or used; or
3. Positive mechanical ventilation prevents ignitable concentrations of flammable gases or vapors, but which may become hazardous as the result of failure or abnormal operation of the ventilation equipment; or
4. A location that is adjacent to a Class I, Zone 1 location, from which ignitable concentrations of flammable gases or vapors could communicate unless preventing such communication by adequate positive-pressure ventilation from a source of clean air, and providing effective safeguards against ventilation failure.

Class II Hazardous Locations

Class II locations are those that are hazardous because of the presence of combustible dust. OSHA defines Class II locations as including the following:

(1) Class II, Division 1

A Class II, Division 1 location is a location:

1. In which combustible dust is or may be in suspension in the air under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures; or
2. Where mechanical failure or abnormal operation of machinery or equipment might cause the production of such explosive or ignitable mixtures, and might also provide a source of ignition through the simultaneous failure of electric equipment, through the operation of protection devices, or from other causes; or
3. In which combustible dust of an electrically conductive nature may exist.

Note to the definition of “Class II, Division 1:” This classification may include areas of grain handling and processing plants, starch plants, sugar-pulverizing plants, malting plants, hay-grinding plants, coal pulverizing plants, areas producing or processing metal dust and powders, and other similar locations that contain dust-producing machinery and equipment (except where the equipment remains dust-tight or vented to the outside).

These areas would have combustible dust in the air, under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures. Electrically nonconductive combustible dust includes dust produced in the handling and processing of grain and grain products, pulverized sugar and cocoa, dried egg and milk powders, pulverized spices, starch and pastes, potato and wood flour, oil meal from beans and seed, dried hay, and other organic materials which may produce combustible dust when processed or handled.

Dust containing magnesium or aluminum remains particularly hazardous, and the necessary use of extreme caution avoids ignition and explosion.

Class II, Division 2

A Class II, Division 2 location is a location where:

1. Combustible dust will not normally be in suspension in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations will normally be insufficient to interfere with the normal operation of electric equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment; and
2. Resulting combustible dust accumulations on, in, or in the vicinity of the electric equipment may be sufficient to interfere with the safe dissipation of heat from electric equipment or it may be ignitable by abnormal operation or failure of electric equipment.

Note to the definition of “Class II, Division 2:” This classification includes locations where dangerous concentrations of suspended dust would not be likely, but where dust accumulations might form on or in the vicinity of electric equipment. These areas may contain equipment from which appreciable quantities of dust would escape under abnormal operating conditions or be adjacent to a Class II Division 1 location, as described above, into which an explosive or ignitable concentration of dust may be put into suspension under abnormal operating conditions.

Class III Hazardous Locations

Class III locations are those that are hazardous because of the presence of easily ignitable fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures. OSHA defines Class III locations as including the following:

Class III, Division 1

A Class III, Division 1 location handles, manufactures or otherwise uses easily ignitable fibers or materials that can produce combustible flyings.

Note to the definition of “Class III, Division 1:” Such locations usually include some parts of rayon, cotton, and other textile mills; combustible fiber manufacturing and processing plants; cotton gins and cotton-seed mills; flax-processing plants; clothing manufacturing plants; woodworking plants, and establishments; and industries involving similar hazardous processes or conditions.

Easily ignitable fibers and flyings include rayon, cotton (including cotton linters and cotton waste), sisal or henequen, istle, jute, hemp, tow, cocoa fiber, oakum, baled waste kapok, Spanish moss, excelsior, and other materials of similar nature.

Class III, Division 2

A Class III, Division 2 location allows storage or handling of easily ignitable fibers other than in the process of manufacture.

Is Your Jobsite a Hazardous Location?

It’s important to know what class and division you’re working in. Be on the lookout for technological advances in intrinsically safe equipment that will make you—and everyone around you—safer and more efficient.