Intrinsic safety (IS) is defined as a protection technique based on the restriction of electrical energy to a level which is too low to be able to ignite an explosive atmosphere. The author describes some of the principles involved. It differs essentially from all other methods of protection of electrical apparatus for use in potentially explosive atmospheres because the flow of energy from the safe area must be carefully controlled. Its growth has been greatly accelerated by the development of barrier devices which protect the hazardous area from the effects of possible intrusion of dangerous sources of energy from the safe area parts of the system. In future it is possible that fibre-optic transmission of data will supersede many existing barrier applications for IS systems.
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