Electrical Hazardous Area Classifications for Cement Plants

Cement plants commonly use pulverized coal and coke as fuel for their kilns. Unlike natural gas and oil, foreign elements within various forms or ranks of coal present many hazards and affect the electrical hazardous area classification. Clouds of coal dust and coke dust can ignite or explode. Areas where these dusts always exist or would only exist under abnormal conditions are classified by nationally recognized codes and standards as Class II, Group F, Divisions 1 or Division 2 respectively. Coal often contains pockets of methane. Without adequate ventilation, the areas where methane exists are classified as Class I, Division 1, Group D. Even worse, some coals contain pyritic sulfur. Coal must be monitored and stored in a way that will permit fire fighters to put out coal fires. Under certain conditions, coal will spontaneously combust and burn by itself.' When determining if coal dust or coke dust will always exist or would only exist under abnormal conditions when classifying Class II areas as Division 1 or Division 2, consideration should be given to the types of electrical equipment that would normally be installed in the areas. Often electrical equipment and installation methods that are commonly used in cement plants for unclassified areas meet the 2008 NEC
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requirements for Class II, Division 2 areas. Sometimes for little additional cost, equipment and installation methods that meet the requirements for Class II, Division 1 areas can be used, thereby eliminating a need to rely on engineering judgment when classifying areas as Division 1 or Division 2. Classifying Class II areas presents additional challenges because, unlike vapors and gases, dusts are always present and it is often impossible or impractical to keep areas clean. If one can see a footprint of combustible dust on the floor, there is enough combustible dust to cause an explosion!