ABSTRACT
When fieldbus technology is applied in fire hazard plants like chemical and petrochemical industries, it is segregated into hazardous area and safe area. Intrinsically safe (IS) barrier is employed in hazardous area to overcome this. The different barriers are entity concept, fieldbus intrinsically safe concept (FISCO), high power trunk concept (HPTC), and dynamic arc recognition and termination (DART).
Hazardous area classification is based on identification and quantity of flammable materials, their characteristics and chances of their coming into contact with electrical arc. Two classifications are employed: division classification system and zone classification system.
In entity concept, low power is used at the barriers limiting the number of devices to be employed to a few. Complex and time-consuming calculations do not find favor with the users to employ this method. FISCO model allows employing more devices per segment due to more power. No detailed calculations are needed in this method. HPTC employs more power and removes the limitation with regard to segment length and number of devices. HPTC has advantages like: devices can be serviced without “hot work” permit, standard power supplies can be employed, entity and FISCO compliant devices can be mixed, etc. DART ensures normal power availability in IS applications but disconnects the system in case of fire by sensing the highly deterministic di/dt during critical phase.
