Areas classification

TABLE 25-7 Ozone Nonattainment Area Classifications and Associated Requirements... 

Nonattainment area classification One-hour ozone concentration design value, ppm Attainment date Major source threshold level, tons VOGs/yr Offset ratio for new/modified sources... 

Check area classification and verify that electrical equipment is properly rated... 

The compressor or blower installation in a typical refinery or chemical process unit is not out-of-doors completely. Some form of shelter often is provided, ranging from only a roof to a completely closed building. When process equipment such as a centrifugal gas compressor, which is not hazardous in normal operation, is present in the shelter, the hazard classification depends on the extent to that which the shelter restricts ventilation. The extent of the shelter provided determines the area classification and the type of motor enclosure that should be applied. 

Examples of electrical area classification for various operations... 

Electrical area classification distances Process Plant Layout pages 568-577... 

The vendor shall be responsible for the selection of proper range, pressure rating, materials of construction and electrical enclosure based on process conditions and electrical area classification. All instruments and controls shall be in accordance with Specification ME-0-JN400. 

Another common mistake often uncovered is electrical equipment w hich is not consistent with the design area classification. See Chapter 17. 

The European philosophy on area classification varies from that of the United. States and Canada. Specifically, in Europe and most other inter national areas, the Zone concept is utilized. An area in which an expio sive gas-air mixture is continuously present, or present for long perioiK of time, is referred to as Zone 0. The vapor space of a closed, but vented, process vessel or storage tank is an example. An area in which an explosive gas-air mixture is likely to occur in normal operations is designated Zone 1. An area in which an explosive gas-air mixture is less likely to occur, and if it does occur will exist only for a short time, is designated Zone 2. Zone 0 and Zone 1 correspond to Division 1 in the U.S. and Canada System. Zone 2 is equivalent to Division 2. 

To promote uniformity in area classifications for oil and gas drilling and producing facilities, the American Petroleum Institute developed RP 500, Recommended Practice for Classification of Locations for Electri cal Installations at Petroleum Facilities Classified as Class 1, Division 1. and Division 2. Figures 17-4 to 17-14 show some common recommended classifications surrounding common production facility equipment as given in RP 500. API RP 500 also provides valuable tutorial information on the philosophies of area classification and the reader is encouraged to become familiar with this publication. 

Based on the information contained in these figures it is possible to draw an area classification diagram of the facility. Figure 17-15 shows an example for a typical offshore production platform. 

Electrical switches, relays, and other devices are described for safety reasons by several general categories. Since these devices are potential sources of ignition during normal operation (for example, arcing contacts) or due to malfunction, the area classification limits the types of devices which can be used. 

Instrument Purging for Reduction of Hazardous Area Classification... 

Cascading effects Check valve Clogged (of filter) Consensus standard Conservation vent Dike, berm Discharge valve Division (in electrical area classification) Downspout Expansion joint Explosion proof Faucet... 

The NEC group method for classifying flame arresters is similar to that used for electrical area classification. NFPA 497 (1997) provides the criteria for classilying gases into NEC groups for suitability for electrical area classification. 

Electrical area classification AIA, ANSI, API, CMA, FIA, FM, NFPA, NSC, OIA, OSHA, USCG... 

If Article 505 is used, area classification, wiring, and equipment selection shall be under the supervision of a qualified Registered Professional Engineer. 

For purposes of testing, approval, and area classification, various air mixtures (not oxygen-enriched) shall be grouped in accordance with Sections 500-3 (a) and 500-3 (b). 

Exception Where area classification is in accordance with Article 505, the temperature marking in Section 505-10(b) shall not exceed ignition temperature of the specific gas or vapor to be encountered. 

FPN No. 1) As a guide in determining when flammable gases are present continuously, for long periods, or under normal conditions, refer to. Recommended Practice for Classification of Locations for Electrical Installations of Petroleum Facilities, API RP 500-1991, Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous Areas, lEC 79-10 and. Institute of Petroleum Area Classification Code for Petroleum Installations, IP 15. 

FPN) The area classifications listed in Table 515-2 are based on the premise that the installation meets the applicable requirements of Elammable and Combustible Liquids Code, NFPA 30-1993 (ANSI), Chapter 5, in all respects. Should this not be the case, the authority havingjurisdiction has the authority to classify the extent of the classified space. 

After an area classification has been established, then anelectrical equipment, instruments, and wiring must adhere to that classification. Therefore, some motor enclosure types would not be electrically acceptable for specific area classifications. 

If the pumps are located indoors, a Division 1 classification is likely to apply. Motors must be Class 1, group D, explosion-proof, or they may be separately ventilated with clean outside air brought to the motor by fans. Auxiliary devices such as alarm contacts on the motor must be suitable for the area classification. The installed costs, overall efficiencies, and service factors associated with the enclosures that are available will influence the selection. 

Vapour source Extent of classified area Area classification... 

Electrical area classification distances Distances for storage of explosives... 

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