In the USA the The National Electrical Code (NEC) 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.”
Class I Locations A “Class I Location” is created by the presence of flammable gases or vapors 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. Some typical Class I locations are: · Petroleum refineries, and 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; and · Utility gas plants, and operations involving storage and handling of liquified petroleum gas or natural gas.
Class II Locations The second type of hazardous location is called a “Class II Location”. This classification is created by the presence of combustible dust in the air in sufficient quantities to be explosive or ignitable. 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.
Class III Locations The third type of hazardous location is called a “Class III Location”. This classification is created by the presence of easily ignitable fibers or flyings. Typically these fibers and flyings are not 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; · Cotton seed mills, flax processing plants; and · Plants that shape, pulverize or cut wood and create sawdust or flyings. Sources of Ignition Previously, we’ve established the fact that electrical equipment can become a source of ignition in a hazardous location. Typically there are three root 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) Equipment Design and Construction Standards have been developed that identify what equipment may be used in the hazardous locations. As you might expect, what equipment you can install will be based on the Classification (i.e. Class I, Class II or Class III) of the hazardous location.
Remember you are COMPETENT and Trained what is the right answer?
1. Areas defined as “Hazardous” will: a. Be documented b. Documentation will be available c. Classification under supervision of qualified registered engineer d. All the above
2. Areas where flammable gases or vapors are or may be present in the air in sufficient quantities to be explosive or ignitable are classified as: a. Class I b. Class II c. Class III d. Hazardous
3. Areas that are considered hazardous because of the presence of combustible fibers are classified as: a. Class 1 b. Class 11 c. Class 111 d. Hazardous
4. Areas that are considered hazardous because of the presence of combustible dust are classified as: a. Class 1 b. Class 11 c. Class 111 d. Hazardous
5. Equipment shall be approved not only for the class of location, but also for the ignitable or combustible properties of the specific gas, vapor, dust, or fiber that will be present. This statement is: a. True b. False
6. What classification would be used at 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. a. Class I, Division 1 b. Class II c. This is not considered a hazardous location d. Class I, Division 2:
7. A facility may contain multiple classifications in various parts of a building. For example the storage room may be classified as Class III and a production area may be classified as a Class 1 Location. Is this statement a. True b. False
8. Equipment, wiring methods, and installations of equipment in hazardous (classified) locations shall be: a. intrinsically safe b. approved or safe for the hazardous (classified) location c. waterproof d. Both a and b