Assuming that methods for avoiding the need for tracing have been considered and rejected, the first step in matching the heat-tracing to the piping system requires an analysis of fundamentals. These include the type of application, suitability and relative cost of different types of heat-tracing, availability of steam and/or electricity, amount of heat loss which must be made up, requirements for temperature control, and classification of the traced area as a hazardous or ordinary environment due to the presence of flammable substances.
AREA CLASSIFICATION
Areas are classified according to their potential fire hazard as defined by Articles 500 to 505 of the National Electrical Code (NEC).48 [In industrial applications, verification that electric components meet NEC hazardous-area requirements is issued by a nationally recognized testing laboratory (NRTL).] Under this system, there are classified and unclassified (ordinary) areas. Hazardous areas have two different classification systems, the old class/division method and the new zone system. The zone system has been used in Europe for many years and is now being included in the International Electrotechnical Committee (IEC) specifications. The old Class/Division system rates locations by class, division, and group. The area class determines the category of combustible atmosphere: flammable gases, vapors, or liquids (Class I); combustible dust (Class II); and combustible fibers (Class III). The division indicates the likelihood of a hazard to be present under different conditions. Hazardous atmospheres with similar combustion properties
are listed in the same group.