In this article, I will cover the classification of a hazardous area which vary with the country to country based on their standard. Here, I will cover North America standard but the purpose of all standards is the protection of human, equipment and environment.
Before moving through this article, I suggest you read my previous article on types of protection used in a hazardous area.
In many industries when you go for an interview you might have faced question based on the hazardous area because they want you to have knowledge of the hazardous area so you can work with safety whenever a situation demands. So, I urge those engineer who wants to join oil and gas industries or chemical plant first prepare yourself with the hazardous area and its classification.
In North America suitability of equipment of hazardous area must be tested by Nationally Recognized Testing Laboratory (NRTL).
Approval agencies in North America classify equipment to be used in hazardous area location by classifying class 1 or 2, Division 1 or 2, Groups A, B, C, D, E, F and G with temperature classes T1 to T6. These are defined in NEC and Canadian Electrical Code (CEC). Let's dig into our main aim of the article.
Class: The general nature of Hazardous material in the surrounding atmosphere is called class.
Class 1: Locations in which flammable gases or vapors are present in sufficient quantities to produce explosive mixtures.
Class 2: Locations which are hazardous because of the presence of combustible dust.
Class 3: Locations where easily ignitable fibre may be present but not likely to be present in such quantities to produce an explosion.
Division: Division shows the probability of hazardous material which is present in an ignitable concentration in the surrounding atmosphere.
Division 1: The region or locations where the probability of the atmosphere being hazardous is too high due to the presence of the flammable material continuously.
Division 2: Locations which are hazardous in an abnormal condition. An abnormal conditions are like failure or defect of any component or equipment.
Group: It defines the hazardous material present in the surrounding atmosphere. There are seven types of group are design to know level of the hazardous material.
Group A: Atmosphere contains chemical like acetylene.
Group B: Atmosphere contains fuel, hydrogen, combustible gases contain more than 30% of hydrogen or gases or vapors of equivalent hazard such as a different category of chemical (acrolein, ethylene oxide, butadiene).
Group C: Atmosphere contains ethyl ether, ethylene or gases or vapors.
Group D: Atmosphere contains acetate, ammonia, benzene, ethanol, gasoline, natural gas, propane, etc.
Group E: Atmosphere contains metal dust including magnesium, aluminium and also similar hazard used in electrical equipment.
Group F: Atmosphere contains charcoal, coal or dust.
Group G: Atmosphere contains flour, grain, wood, plastic and chemicals.
Temperature code: The mixture of gas and air may be ignited by coming into contact with a hot surface.
The NEC states that a surface temperature of 100 C is not required to be marked with the temperature code.
Temperature maximum surface temperature
code °C °F
T1 450 842
T2 300 572
T2A 280 536
T2B 260 500
T2C 230 446
T2D 215 419
T3 200 392
T3A 180 356
T3B 165 329
T3C 160 320
T4 135 275
T4A 120 248
T5 100 212
T6 85 185
Above is the list best on North American standard. This data is taken from the source and not a yield of my mind as a class and a particular standard remain always the same.
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