Hazardous Area Classification (API 500)
Hazardous area classification is a very important concept used by engineer in oil and gas plant. It is very important to know the hazardous area classification especially when we will determine the technical specification of an electrical equipment. For example : the technical specification of induction motor that drive a pump for oil transfer is certainly different with induction motor that drive the pump for water trasnsfer. You can see the example of induction motor for hazardous area application in my post
The main purpose of right equipment selection is safety. To learn about the concept, I suggest you to learn deeply the concept in API 500.
Before going further, i will explain some terms :
- Hazardous area is a location where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitible fibers or flyings.
- Class is regarding the material that exist in the certain area. It can be gas or liquid vapors (class I), dust (class II), and fibers (class III). Actually, not all the liquid is in class I, some liquid can also be in class II. The categorization between class I and class II is based on the flash point. The class I liqud is where the flash point is below 100 F (37.8 C). An example of the class II liquids is diesel fuel.
- Division is regarding the likelihood of the appearance of gas or vapors. It can be division I and division II
- Class I location is a location in which flammable gases or vapors are, or may be, present in the air in quantities sufficient to produce explosive or ignitible mixtures.
- Class I, Division 1 location is a location in which ignitible concentrations of flammable gases or vaports area expected to exist :
- Under normal operating conditions
- Under faulty operation of equipment or process that might simultaneously release flammable gases or vapors
- Class I, Division 2 location is a location in which adjacent to Class I division II.
- Maximum experimental safe gap (MESG) is a term used to specify the equipment technical specification based on the kinds of gas where it is installed. MESG is maximum gap of the joint between the two parts of the interior chamber of test apparatus. According to me, MESG is the
- Gas group is regarding is MESG. The more volatile the gas, the less the size of MESG
The main purposes of API 500 is to explain the method for hazardous area classification while the methods for protection of certain classified area (for example : explosion proof or increased safety) are not explained. Those protection methods are explained in another standards such as : API 505 or IEC 60079. The IEC 60079 explains the concepts of protection comprehensively such as explosion protection, increased safety, intrisically safety, oil encapsulation, sand encapsulation, non-sparking.
The implementation of hazardous area classification is not so difficult. API 500 has given many examples of application. For example for tank application, for vessel application, for floating roof tank application, for jetty application, and so on. Here is some application.
Based on my experience, HAC (hazardous area classification) document is dynamic. The location can be class I div II at the commisioning stage but after 10 years, it can be class I division I because of the high frequency leakage of pump. So many justification needs to be made before applying hazardous area classification of the existing plant.
Can We Change From Class I Division I to Class I Division II?
The drawbacks of placing equipment on class I Division I is the cost. The explosion proof equipment is very expensive. As an alternative, API 500 offers a way to reduce the hazardous area classification from Class I Division I to Class I Division II by using adequate ventilation. The adequate ventilation is defined as ventilation that is sufficient to prevent the accumulation of significant quantities that can lead to explossive. The implementation sometimes uses blower.