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Intrinsic Safety

In industrial processes where flammable or explosive materials are handled, any leak or spill can cause an explosive, dangerous atmosphere. These conditions occur in many industrial environments, most typically those involving petroleum and other chemicals, process gases, metal and carbon dust, alcohol, grain, starch, flour, and fibers. To protect both personnel and plant, precautions must be taken inside these hazardous areas to protect both personnel and plant. In the past, pneumatic controls were used in these environments to avoid the risk of electrical spark. Today, while pneumatic equipment is still used, new technologies and engineering advances have created a wide range of electrical controls which allow far greater functionality, and still maintain a safe operating environment.
Many of these new technologies and advances, as they apply to process measurement and control, fall into a category of engineering known as Intrinsic Safety.

Intrinsic Safety methodology inserts an energy-limiting interface in the wiring between safe and hazardous areas. This restricts the electrical energy in the hazardous-area circuits so that potential electrical sparks or hot spots are too weak to cause ignition. The interface passes signals in both directions but limits the voltage and current that can reach the hazardous area under fault conditions. Intrinsic Safety became popular for many applications in the early 1960s with the introduction of the 'shunt-diode safety barrier' based on the Zener diode, and is now the preferred solution in most applications for several reasons:

Advances in semiconductors allow increasingly complex electrical operations to be carried out in hazardous areas at very low
( typically 1 watt) power levels.
Hazardous-area equipment can be calibrated and serviced 'live'.
Ordinary instrument wiring can be used in hazardous areas.
It is inherently safe for personnel due to the low voltages employed.
International standards governing the design of Intrinsically Safe equipment allow the same product to be sold and used in many countries.
With a certified IS interface, safe-area equipment needs no certification and the user can choose or change the hazardous-area equipment within wide limits.

Regulations governing the installation of electrical equipment in a hazardous area are issued on national, regional, and local levels. In the United States specific regulations from Federal, State, and local agencies must be observed; In Canada, regulations from the national, provincial, and city governments must be followed. In Europe, European Union regulations define the general specifications and methods of protection against explosion, while national requirements primarily cover installation criteria. IT IS ESSENTIAL TO DETERMINE ALL OF THE APPROPRIATE REGULATORY REQUIREMENTS PRIOR TO ELECTRICAL DEVICES IN HAZARDOUS AREAS.

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