Intrinsic safety

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. In signal and control circuits that can operate with low currents and voltages, the intrinsic safety approach simplifies circuits and reduces installation cost over other protection methods. Areas with dangerous concentrations of flammable gases or dust are found in applications such as petrochemical refineries and mines. As a discipline, it is an application of inherent safety in instrumentation. High-power circuits such as electric motors or lighting cannot use intrinsic safety methods for protection.

In normal use, electrical equipment often creates tiny electric arcs (internal sparks) in switches, motor brushes, connectors, and in other places. Compact electrical equipment generates heat as well, which under some circumstances can become an ignition source.

There are multiple ways to make equipment explosion-proof, or safe for use in ex-hazardous areas. Intrinsic safety is one of a few methods available for ex-hazardous areas. Others include explosion proof enclosures, venting, oil immersion, powder and sand filling, and hermetic sealing. For handheld electronics, intrinsic safety is the only realistic method that allows a functional device to be explosion-proof. A device termed intrinsically safe is designed to be incapable of producing heat or spark sufficient to ignite an explosive atmosphere.

There are several considerations in designing intrinsically safe electronics devices: reducing or eliminating internal sparking, controlling component temperatures, and eliminating component spacing that would allow dust to short a circuit. Elimination of spark potential within components is accomplished by limiting the available energy in any given circuit and the system as a whole. Temperature, under certain fault conditions such as an internal short in a semiconductor device, becomes an issue as the temperature of a component can rise to a level that can ignite some explosive gasses, even in normal use. Safeguards, such as current limiting by resistors and fuses, must be employed to ensure that in no circumstance can a component reach a temperature that could cause autoignition of a combustible atmosphere. In the highly compact electronic devices used today PCB's often have component spacing that create the possibility of an arc between components if dust or other particulate matter works into the circuitry, thus component spacing, siting and isolation become important to the design.

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