Question 10

The Correct Answer is A **Explanation of Option A (Correct):** Option A describes the fundamental principle and core definition of intrinsically safe (IS) equipment. Intrinsically safe protection is a method of hazard protection achieved by limiting the energy available to a circuit in a hazardous area (where flammable gases or dusts are present). The energy (both electrical current and voltage) is limited to a level so low that, even under fault conditions (such as a wire breaking and causing a spark, or components failing), any spark or thermal effect produced is incapable of igniting the most easily ignitable concentration of the surrounding flammable atmosphere. **Explanation of Incorrect Options:** **B) an electrical circuit normally limited to instrumentation in hazardous areas:** While intrinsically safe circuits are commonly used for low-power instrumentation (sensors, transmitters, etc.) in hazardous areas, this option describes an application, not the safety mechanism itself. Instrumentation circuits in hazardous areas could also use other protection methods (like explosion-proof enclosures or purging systems) that are not intrinsically safe. **C) electrical circuits under 2 amperes:** An intrinsically safe circuit is not defined solely by current limits. While IS circuits typically operate at very low currents (often in the milliampere range), a circuit operating under 2 amperes could still have sufficient voltage and energy (power = voltage × current) to cause an igniting spark, especially if the voltage is high. The definition relies on total energy limitation, not just an arbitrary current threshold. **D) electrical circuits under 12 volts:** Similar to option C, 12 volts is not an inherent or defining characteristic of intrinsic safety. While IS circuits often operate at low voltages, 12 volts (or even less) combined with high current could still generate enough energy (a high-energy spark or hot surface) to cause ignition. Intrinsic safety is based on stringent testing and verification that the specific energy level—regardless of the voltage or current alone—is below the minimum ignition energy (MIE) of the explosive atmosphere.