Hazardous Classified Locations

OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

HAZARDOUS (CLASSIFIED) LOCATIONS Introduction: A hazardous location is any location where a potential hazard, either a fire or an explosion can exist due to the presence of flammable, combustible, or ignitable materials. These materials can consist of gases, vapors, liquids, dust, fibres, etc. Hazardous locations are classified according to the properties and quantities of the hazardous material which can be present. Hazardous locations are divided into three classes, two divisions, and seven classified groups as follows: Class I, II, III; Division 1 and 2; and Groups A, B, C, D, E, F, and G.

Hazardous Location Types: Class I Locations: An area where flammable gases or vapors are or can be present in the air in quantities sufficient to produce explosive or ignitable mixtures. Some typical Class I locations are: 1Petroleum refineries, and Gasoline storage and dispensing areas 2Dry cleaning plants where vapors from cleaning fluids can be present. 3Spray finishing areas. 4Aircraft hangers and fuel servicing areas; and 5Utility gas plants, and operations involving storage and handling of liquified petroleum gas or natural gas.

Class II Locations: An area where presence of combustible dust present a fire or explosion hazard. Some typical Class II locations are: 1Grain elevators. 2Flour and feed mills. 3Plants that manufacture, use or store magnesium or aluminum powders. 4Producers of plastics, medicines and fireworks. 5Producers of starch or candies.

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OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

Class III Locations An area made hazardous due to 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. Some typical Class III locations are: 1Textile mills, cotton gins. 2Cotton seed mills, flax processing plants. 3Plants that shape, pulverize or cut wood and create sawdust or flyings.

Hazardous Location Conditions In addition to the types of hazardous locations, the National Electrical Code also concerns itself with the kinds of conditions under which these hazards are present. Conditions, first, normal conditions, and, second, abnormal conditions. The Code writers have designated these two kinds of conditions very simply, as Division 1 – normal and Division 2 – abnormal. Class I, Class II and Class III hazardous locations can be either Division 1 or Division 2. Good examples of Class I, Division 1 locations would be the areas near open dome loading facilities or adjacent to relief valves in a petroleum refinery, because the hazardous material would be present during normal plant operations. Closed storage drums containing flammable liquids in an inside storage room would not normally allow hazardous vapors to escape into the atmosphere but, what happens if one of the containers is leaking? You have got a Division 2 - abnormal- condition …. A Class I, Division 2 hazardous location.

Nature of Hazardous Substances *

The gases and vapors of Class I locations are broken into four groups by the Code: A, B, C and D. These materials are grouped according to the ignition temperature of the substance, its explosion pressure, and other flammable characteristics.

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OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

Group A: Group A is an atmosphere containing acetylene. Equipment with a rating up to 536º F (280º C) can be utilized. Group B: Group B is an atmosphere containing hydrogen, or gases or vapors with a hazard equal to hydrogen. Butadiene, and ethylene and propyleneoxides are included in this group. Equipment with a rating to 536º F (280º C) can be utilized. Group C: Group C is an atmosphere containing cyclopropane, ethyl ether, or ethylene or gases or vapors with a hazard equal to these gases. Equipment with a rating to 356º F (180º C) can be utilized. Group D: Group D is an atmosphere containing acetone, alcohol, benzine, butane, gasoline, propane, natural gases or gases with vapors with a hazard equal to these gases. Equipment with a rating to 536º F (280º C) can be utilized. *

In Class II – dust locations – we find the hazardous materials in Groups E, F, and G. These groups are classified according to the ignition temperature and the conductivity of the hazardous substance. Conductivity is an important consideration in Class II locations, especially with metal dusts.

Group E: Group E is an atmosphere containing combustible metalic dust or other dust with a similar hazard that is equivalent., such as Aluminium and Magnesium dusts. Group F: Group F is an atmosphere containing Carbon Black, charcoal coal, or coke dusts with 8% or less total volatile material. Group G: Group G is an atmosphere containing grain dusts, flour, starch, cocoa, and similar types of materials.

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OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

Hazardous Location Equipment Sources of Ignition The ways in which electrical equipment can become a source of ignition. There are three of them. 1-

2-

3-

Arcs and sparks produced by the normal operation equipment, like motor starters, contactors, and switches, can ignite a hazardous location atmosphere. The high temperatures of some heat-producing equipment, such as lamps and lighting fixtures, can ignite flammable atmospheres if they exceed the ignition temperature of the hazardous material. Electrical equipment failure a burn out of a lamp socket or shorting of a terminal could spark a real disaster in a hazardous location.

REQUIREMENTS FOR EQUIPMENT USED IN HAZARDOUS LOCATIONS Equipment for Class I Locations The primary concern of Class I locations is the presence of an arc, spark or high temperature that could ignite the hazardous liquid or vapor present. When possible, electrical systems that produce an arc or spark should not be installed in a Class I location to prevent a fire or explosion. But if this is not feasible, there are acceptable procedures and systems for protecting against fire or explosion under the conditions of both divisions. The equipment used in Class I locations are housed in enclosures designed to contain any explosion that might occur if hazardous vapors were to enter the enclosure and ignite. These closures are also designed to cool and vent the products of this explosion as to prevent the surrounding environment from exploding. The lighting fixtures used in Class I locations must be able to contain an explosion as well as maintain a surface temperature lower than the ignition temperature of the surrounding hazardous atmosphere. 1- Intrinsically safe or nonincendiary systems hold energy available in a circuit exposed to flammable vapors or gases so

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OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

low that it is incapable of ignite the specific hazardous atmosphere in which it is present. 2- Explosionproof apparatus are instruments enclosed in a case capable of withstanding an explosion inside without igniting flammable material outside, they also operate at an external temperature too low to ignite combustible material surrounding them. They are neither gas-tight nor vapor-tight, but are flametight to prevent an inner explosion from reaching the atmosphere. Explosionproof housings are especially useful in all Division 1 areas. 3- Purging is the use of nonflammable gases to flush flammable gases or vapors from an enclosed space so that the vessel or space involved can be opened or used for fuels without danger of an explosion. The nonflammable gas displaces the flammable substance toward the vents. Carbon Dioxide is commonly used for this purpose and amount used varies with molecular weight of the substance being purged. 4- Inerting consists of mixing a chemically, nonflammable gas with flammable substance, thereby displacing oxygen until the percentage of oxygen in the mixture is too low to allow combustion. As in purging, inerting requires the safe disposal of vented flammable gases. 5- Encapsulation encloses a component or assembly in a solid or semi-solid medium, such as tar, wax or epoxy. It can be considered safe if the medium effectively seals the ignition source from the atmosphere. 6- The techneque of oil immersion is not likely be used on a complete instrument, as sealing and encapsulation might.

Equipment for Class II Locations Class II locations make use of equipment designed to seal out dust. The enclosures are not intended to contain an internal explosion, but rather to eliminate the source of ignition so no explosion can occur within the enclosure. These enclosures are also tested to

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OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

make sure they do not overheat when totally covered with dust, lint, or flyings. Only electrical equipment in enclosures that are both ignition resistant and impervious to dust are suitable for locations containing a combustible dust hazard. Apparatus and equipment for Class II hazardous locations are subjected to specific dust-air mixtures in the joints in the enclosure, clearances at shafts, etc., to make sure they are dust-tight. 1- To prevent combustible dust from entering an enclosure, pressurization can be used. Pressurization is similar to purging, where an inert gas or clean air is supplied to an enclosure at a sufficient pressure, to keep dust from entering. Unlike purging, however, pressurization cannot bring an enclosure to a safe level once dust is inside. When this occurs, the enclosure must be opened and the dust removed. 2- Purging uses positive pressure to exclude dust and prevent build-up of insulating dust layers on contacts. 3- Oil immersion is suitable against dust hazards, but the process must also be dust-tight.

C.

Equipment for Class III Locations: Equipment used in Class III locations needs to be designed to prevent fibers and flying s from entering the housing. It also needs to be constructed in such a way as to prevent the escape of sparks or burning materials. It must also operate below the point of combustion. High temperatures are the primary concern of electrical equipment installed in Class III locations. Surface temperatures of equipment shouls not be high enough to cause excessive dehydration in the hazardous location so as to cause accumulated fibers or flyings to ignite spontaneously.

International Comparison HAZARDOUS NEC U.S. MATERIALS STANDARDS Gas or Vapor Class I Division 1 Class I Division 2 Dust Class II Division 2 Class II Division 2 Fibers or Flyings Class III Division 1 6

IEC STANDARDS Zone 0 Zone 1 Zone 10 Zone 11 Zone 10

OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

Class III Division 2

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Zone 11

OSHA

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION U.S. DEPARTMENT OF LABOR

Wagdi Fouad Seffain – Authorized OSHA Trainer

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