Intrinsically Safe Systems-Trends in Design and Installation Standards

Intrinsic safety is a mature proven method to achieve a safe installation of electrical apparatus in a location made hazardous by the presence of flammable or combustible materials. Standards for intrinsically safe apparatus are still evolving. Underwriters' Laboratories, Inc. Standard 913-1975 and NFPA 493-1975 are the most complete statement of requirements for intrinsically safe apparatus and systems yet published. The forthcoming Instrument Society of America Recommended Practice on installation of intrinsically safe systems will fill a pressing need for an installation guide. The National Electrical Code is also changing to recognize the needs of those in the process industries who use intrinsically safe systems and similar apparatus. Much yet needs to be done to define design constraints and Construction requirements for intrinsically safe apparatus. This work is underway.