Hazardous Area Electrical Requirements

Workstation Environments (Fabrication Area). Electrical equipment and devices within five feet of workstations in which flammable liquids or gases are used shall be in accordance with the Electrical Code for Class I, Division 2 hazardous locations, except when the air removal from the workstation or dilution will provide nonflammable atmospheres on a continuous basis (UFC 5104.5). The requirements for hazardous locations need not be applied when the average air change is at least four times that set forth in UBC 307.11.2.4 (UBC 307.11.2.6). The volumes of air moving through and exhausted from a cleanroom t5 ically meet the requirements of these exceptions. If the air volume is sufficient, continuous, and on emergency power, the electrical installation within five feet of the workstation will not have to meet the requirements of Class I, Division 2 locations. 

HPM Storage Facilities. Explosion-proof electrical apparatus is required in rooms where a flammable atmosphere may occur. Electrical wiring and equipment located in HPM storage rooms shall be approved for Class I, Division 1 hazardous locations, and shall be in accordance with the Electrical Code. Exception When separate storage rooms are used, the storage rooms without flammable liquids or gases need not be approved for Class I, Division 1 hazardous locations (UFC 5108.2.8). 

In rooms where the flammables are stored in monitored, Z-purged and protected (sprinklered) gas cabinets. Class I, Division 1 requirements may not apply for general electrical apparatus in the storage room. In a properly designed gas cabinet, all flammable gases are contained within the 

In addition to Section UFC 8003.1.10.2, electrical wiring and equipment in storage areas for p5Tophoric gases and liquids shall comply with the requirements for Class I, Division 2 locations. (UFC 8003.8.1.3). 

If the fab has a solvent exhaust system with a solvent abatement system, the area around the solvent abatement facility must be in compliance with NFPA Article 36. 

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The relevant standards have been affected by the standard harmonisation process within the EU through the European Committee for Electrotechnical Standardisation (CENELEC) and through the International Electrotechnical Commission (lEC). Individual parts of BS EN 60079 deal with different aspects concerning electric apparatus for potentially explosive gas atmospheres, namely classification of hazardous areas, electrical installations in hazardous areas (other than mines) and inspection and maintenance of electrical installations in hazardous areas (other than mines). BS 50014 covers general requirements. 

Fusible Link a mechanical release device actiwited by the heat effects of a fire. It usually consist of two pieces of metal joined by a low melting solder. Fusible links are manufactured as various incremental temperature ratings and are subjected to varying normal maximum tension. When installed and the fixed temperature is reached, the solder melts and the two metal parts separate, initiating the desired actions Hazard Analysis the systematic identification of chemical or physical characteristics and/ or processing conditions and/or operating conditions that could lead to undesired events Hazardous Area, Electrical a US classification for an area in which explosive gas/air mixtures are, or may be expected to be, present in quantities such as to require special precautions for the construction and use of electrical apparatus HAZOP an acronym for Hazard and Operability study, which is a qualitative process risk analysis tool used to identify hazards and evaluate if suitable protective arrangements are in place if the process were not to perform as intended and unexpected consequences were to result... 

Tayout also has a significant role in minimizing the probability of ignition of a flammable release. Area electrical classification provides the basis for the control of electrical ignition sources. This classification is also used to determine the areas that require protection from vehicular access, etc. Frequently, highly hazardous processes that can result in overpressure (e.g., hydrogenation) are placed behind blast resistant structures/walls. 

The use of electrical equipment in hazardous areas is covered by British Standards BS 5345 and BS 5501. The code of practice, BS 5345, Part 1, defines hazardous areas as those where explosive gas-air mixtures are present, or may be expected to be present, in quantities such as to require special precautions for the construction and use of electrical apparatus. Non-hazardous areas are those where explosive gas-air mixtures are not expected to be present. 

Safety Barriers. Figure 1 illustrates an application employing intrinsically safe electrical circuits for the demilitarization of ammunition. Three separate areas are required for this application - one area, classified as non-hazardous, to serve as the control and loading area a second area, classified as hazardous, where the actual demilitarization is accomplished and a third area, classified as non-hazardous, is required for the hydraulic pump due to the level of noise produced. 

All electrical equipment and wiring installed in hydrogen gas transmission and distribution compressor stations shall conform to the requirements of NFPA 70, insofar as the equipment commercially available permits. Electrical installations located in hazardous areas, as defined in NFPA 70, and that are to remain in operation during compressor station emergency shutdown, as provided in para. I-1.3.2.1(a), shall be designed to conform to NFPA 70 for Class I, Division 1 requirements. 1-1.3 Compressor Station Equipment... 

Personal electronic or electrical devices that may require control are pagers, cellular phones, personal digital assistants (PDAs), and personal radios or music players. Few, if any, of these devices are evaluated to determine if they may be safely used in hazardous areas. Typically, such devices do not claim to be "intrinsically safe" or of "nonincendive circuit" design (NFPA 70, Articles 500 and 504). 

Emergency alarm system design and installation should be in accordance with NFPA 72. Electrical aspects of the fire alarm systems should be designed and installed in accordance with NEPA 70. When devices are located in hazardous areas, they should meet the electrical requirements suitable for that hazardous area. 

Positive displacement pumps can be built to run on 440-V three-phase service, 220-V service or 110-V single-phase service. The site of electrical service may be restricted in some fuel production and distribution areas. Often, explosion proof enclosures and associated equipment must be used when locating equipment in a hazardous area. If explosion-proof equipment is required, the cost of the equipment will increase significantly. 

TGL Technische Gute- und Lieferbedingungen, Technical Regulations for Quality and Delivery) have defined the classification of hazardous areas (TGL 30042) and the requirements for construction and testing of explosion protected electrical equipment (mainly TGL 19491). 

As a rule, they are installed in the safe area as associated apparatus. They are used to limit the electrical values for sensors, actuators etc. located in the hazardous area to levels permissible for intrinsic safety. A certificate is required each time. 

Design for Hazardous Areas. This type of area classification tends to simplify the electrical design by directive means, but poses alternate choice problems, dictated by economics. The cost of an explosion-proof installation is as much as twice that using standard equipment. As an example of more costly electrical equipment, rigid metal conduit with threaded explosion-proof boxes and fittings are required for all Class I, Division 1, hazardous locations either rigid metal conduit or electrical metal tubing is approved for both Class I and II, Division 2, locations. 

Where a four-wire supply is needed in a hazardous area it is necessary to use four-pole circuit breakers and isolators so that the neutral is completely isolated when maintenance work is required to be undertaken. If the neutral is not electrically separated and a fault occurs elsewhere in the same network then the neutral in the hazardous area could have its potential elevated sufficiently above zero to cause a spark (or even an electric shock). This aspect is especially important when a switchboard or motor control centre is supplied from more than one source such as two parallel transformers. 

The electrical engineer is not usually involved in the chemistry of the system, his work is mainly associated with sizing the AC and DC cables, accounting for the power requirements and ensuring that the equipment satisfies any hazardous area requirements that may exist. 

Cooling tower. The electric motors driving fans on cooling towers tend to be difficult to maintain if it is required that they also should be flameproof. Such a requirement is likely since flammable solvent from a condenser leak is liable to be returned to the cooling tower. Furthermore, the leakage is liable to reach the pond beneath the cooling tower so this should be installed in the hazardous area. 

Safety interlocks, common to machinery, provide a means either of preventing operator access to a hazardous area until the hazard is removed or of automatically removing the hazardous condition (i.e., electric shock, moving parts) when access is gained. Safety interlocks have special requirements, such as fail-safe design, positive opening, and nonoverridable type. 

Most flammable liquids only form an explosive mixture between certain concentration limits. Above and below this level of concentration the mix will not explode. The lowest temperature at which sufficient vapour is given off from a flammable substance to form an explosive gas-air mixture is called the flashpoint. A liquid which is safe at normal temperatures will require special consideration if heated to flashpoint. An area in which an explosive gas-air mixture is present is called a hazardous area, as defined by the British Standards, and any electrical apparatus or equipment within a hazardous area must be classified as flameproof. 

The pH meters used for continuous industrial measurement commonly have a standard 4-20 mA output. The amplifier unit will usually drive a separate display element remote from the measurement point. The pH electrode needs to be close to the amplifier since the electrode has very high impedance and hence requires short leads and careful screening. The amplifier will need to be protected against its environment and also the environment will need to be protected from the electrical hazard posed by the amplifier. Suitable intrinsically safe pH amplifier systems can be obtained commercially. Only the electrodes and the amplifier need to be located in the hazardous area where the measurement is taking place whereas the other equipment and display element can be located in a safe area. 

The particular zone determines the types of protection required for electrical equipment in use in that zone. Ideally, the prime method of protection should be to exclude electrical apparatus from any hazardous area. However, where this is not practical or economic, the next consideration should be whether the electrical apparatus can be segregated by fire-resistant impermeable barriers. Where the installation of electrical apparatus in hazardous areas is unavoidable, the following types of protection may be used according to the circumstances ... 

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