"The areas to which this publication applies are those in which flammable petroleum gases and volatile liquids are: a@ processed; b@ stored; and@ c@ loaded@ unloaded@ or otherwise handled in petroleum refineries. Refinery processing facilities consist of specialized equipment within which liquids or vapors are continuously processed at high rates and at elevated temperatures and pressures. Both chemical and physical changes occur in these materials@ and during ""abnormal"" conditions the composition and properties of stocks may change drastically. These conditions@ together with considerations of operating continuity@ dictate standards of refinery design that are not warranted in other operations of the petroleum industry. However@ although these recommendations are applicable only to refinery areas@ it is recognized that a modem refinery encompasses facilities which extend beyond the scope of historically accepted refining operations. Very often@ petrochemical and chemical facilities are interrelated both physically and by process procedure with refining equipment. The practices recommended in this publication can be applied to these additional facilities to the extent that such physical relationships or similar environmental aspects exist. Purpose The NEC is widely used as a guide to good electrical practices and has been adopted as law at various state and local levels. Most installations@ regardless of legal considerations@ conform as a matter of good practice. Therefore@ this recommended practice is not an attempt to rewrite or otherwise supersede the NEC or other applicable codes or ordinances. The NEC has established criteria for classifying areas. Once an area has been classified@ there is little difficulty in understanding the equipment requirements because the NEC specifies the type to be used. The real problem is to determine the existence@ degree@ and extent of classified areas. The purpose of this publication is to assist in the application of NEC criteria to petroleum refinery electrical work."