.ise  .intrinsically safe  .exi

Intrinsically safe equipment:

Electric arc or spark on flammable vapor increases the energy of the vapor and air locally so that particles are activated and creates a violent chemical reaction which is known an explosion. A weak spark does not have sufficient thermal energy to heat the local flammable mixture. Because energy generation rate is slower than energy dissipation rate. so no explosion occurs.

An intrinsically safe circuit is one that is designed for a power so low that any spark produced by it is incapable of igniting the flammable gas.

Intrinsically safe equipment uses such circuit. It is unable to produce strong enough spark to create explosion.

Intrinsically safe equipment is made into two standards. Ex-I(a) and Ex-i(b). Ex-i(a) is used in more hazardous area while Ex-i(b) used in less hazardous area. This method of protection is suitable for electrical supplies at less than 30 volts and 50 miliamps. It is used for instrumentation and control functions.

Design:

The equipment and system design in such a way that capacitance and inductance is kept minimum, to prevent storage of electrical energy which could generate spark. Ex-I devices cables are not permitted to keep in the same tray as other cables.

The whole system is earthed and protection is provided by shunt diode safety barriers between hazardous and non-hazardous area. The safety barriers have current limiting resistors and voltage by-passing Zener diodes to prevent excessive electrical energies from reaching the hazardous area. Intrinsically safe equipment is needed to be certified by administration.