ISA Certified Control Systems Technician (CCST) program

CCST

Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.

CCST question

The purpose of an intrinsic safety barrier is to:

A. provide a physical obstruction between the hazardous and nonhazardous areas.
B. establish a central grounding point in the hazardous area.
C. prevent excess voltage or current from reaching the hazardous area.
D. increase the resistance in the circuit to reduce the risk of explosion.

CCST Answer

The correct answer is C: Prevent excess voltage or current from reaching the hazardous area.

Intrinsic safety (IS) is a protection technique for safe operation of electrical equipment in hazardous areas by limiting the energy, electrical and thermal, available for ignition.

Energy = Power x Time

For electrical energy, Power (Watts) = Volts x Amps

Therfore, to limit energy to a sensor or device, the eletrical power must be limited. Electrical power is limited by limiting the voltage and amperage in the circuit.

An intrinsic safety barrier, when installed properly, will limit the amount of energy that reaches the hazardous area to a value which is insufficient to cause ignition.

Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition (2005), ISA Press