AutoQuiz: What Is the Purpose of an Intrinsic Safety Barrier?

The post AutoQuiz: What Is the Purpose of an Intrinsic Safety Barrier? first appeared on the ISA Interchange blog site.

AutoQuiz is edited by Joel Don, ISA’s community manager.

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

What is the purpose of an intrinsic safety barrier?:

a) provide a physical obstruction between the hazardous and non-hazardous areas
b) establish a central grounding point in the hazardous area
c) prevent excess voltage and current from reaching the hazardous area
d) increase the resistance in the circuit to reduce the risk of explosion
e) none of the above

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The correct answer is C, prevent excess voltage and current from reaching the hazardous area. In order for ignition to occur, three elements are required: Fuel (something to burn-gas, vapor, or powder), an oxidizer (air or oxygen), and an ignition source (electrical or thermal). An intrinsic safety barrier is designed to remove the last element-an ignition source-from the equation. Without an ignition source, there can be no ignition or combustion.

Answer A is incorrect because just providing a physical obstruction between the hazardous and non-hazardous area does not eliminate any of the three elements required for ignition.

Answer B is incorrect because a common ground does not guarantee that a voltage or current less than what is required for ignition will not be present.

Answer D is incorrect because resistance does not necessarily reduce the overall energy in the circuit.

Reference: ANSI/ISA-60079-0 (12.00.01)-2005 – Electrical Apparatus for Use in Class 1, Zones 0, 1 & 2 Hazardous (Classified) Locations

Source: ISA News