De-Mystifying Intrinsically Safe Systems - ISA EXPO 2000

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Intrinsic Safety is not a new concept. It has long been an accepted method of protecting electronic instrumentation located in hazardous areas. Why then is it so often misunderstood? Perhaps the answer lies in the “use only at the last resort” philosophy adopted when dealing with Intrinsically Safe systems. This was a natural approach, when considering the extra level of documentation required to ensure I.S. “system
certification,” the risk of violating the safety of the I.S. system through component substitution or incorrect installation practices, and the relative simplicity and availability of explosion proof devices. Today however, as advances in technology have increased the number of low powered devices used in hazardous areas, the use of Intrinsic Safety has also increased. Intrinsic Safety, once a rare bird, is being used to protect instruments supplied as the “standard product offering.” Intrinsically Safe loops are appearing as part of Radar Tank Gauging (RTG) systems, analyzer systems, loading arm control systems, and most recently in multi-drop HART and Fieldbus loops. The following paper de-mystifies the use and certification of Intrinsically Safe systems. A summary of the Intrinsic Safety concept is provided, a description of options available to certify I.S. systems offered, and the special installation requirements for I.S. systems highlighted. As we are faced with Intrinsically Safe instruments in ever growing numbers, an understanding of the restrictions and added level of complication associated with Intrinsically Safe systems is critical to ensure they are designed, certified, and installed properly. Everyone must understand that just because an instrument carries an Intrinsically Safe certification does not guarantee Intrinsic Safety when installed. Through improper installation or component substitution, an innocent “certified” Intrinsically Safe instrument can become a dangerous ignition source.

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