Hazardous areas Equipment

American practice Certification of Hazardous Area Equipment Marking of Equipment Nameplates References... 

Table 10.4. Enclosure codes for hazardous area equipment...

The maintenance procedures for working with Ex d equipment need to be exercised with care so that the machined surfaces are not degraded or damaged. BS5345 was introduced in 1976 to address this and similar subjects. See Reference 4 for practical view of the problems involved with maintenance of hazardous area equipment. 

The introduction of BS5345 in the mid-1970s focused attention on maintenance and installation of hazardous area equipment for the first time. It placed responsibility on the user of equipment in addition to that which already existed for the manufacturers. 

The harmonisation process has been managed by the Committee of Electrotechnical Standardisation (CENELEC) in Europe. The committee standardises many subjects of electrical and electronic engineering, not only those pertaining to hazardous area equipment and its installation. When eqnipment is certified in accordance with a CENELEC standard the symbol Ex is modified to become EEx . This serves to give the designer and the user extra confidence in the certification. 

Hazardous area equipment that has been tested and approved by a recognised laboratory should have a marking plate attached to its surface, in a place easily seen by the user. This plate is usually the nameplate that shows the normal information such as the name of the manufacturer, voltage, rated power, full load current, frequency, model number, serial number, ambient temperature and date of manufacture. The additional information to be shown for the hazardous area application, should be at least the following ... 

Short circuits often develop from faults of a leakage nature. It is therefore advisable to provide each sub-circuit with an earth leakage current relay or alarm unit, which has a sensitivity that adequately coordinates with other devices. Indeed this is a necessary requirement for sub-circuits that feed power to hazardous area equipment. The use of these earth leakage current relays and detectors will greatly increase the confidence that can be placed on the overall performance of the system of protective devices in the UPS. 

EEx 0 or EEx Certification symbol for hazardous area equipment, with European... 

In India, the Central Mining Research Institute, Dhanbad carries out this testing and provides the necessary certilication for motors used iti explosive atmospheres. But for approval of the equipment, whether it is worthy of use in a particitlar hazardous area, there are accredited agencies.. Some of these are Directorate General Mines Safety. Dhanbad, Chief Controller of Explosives. Nagpur and Directorate General of Factory Advice Service and Labour Institute. Bonibav. 

A motor used in standby operation mode should be equipped with a space heater to keep the motor windings dry. In classified areas these space heaters must meet the surface temperature requirement of the specific hazardous area. 

Since many chemical plants have severe health hazards, it is essential to provide medical facilities and first aid stations. In addition, showers and eye wash stations are necessary in certain hazardous areas. Also, guards and covers should be provided for all moving equipment. Ten of the key protective equipment are listed below. 

Type and specifications on fan driver, gear types, pow er voltage, phase, cycles. Motors should at least meet specifications equivalent to totally enclosed, fan cooled, or if in explosive hazardous area, TEFC Class I, Group D (except this not acceptable in hydrogen or acetylene atmosphere). Due to moisture conditions around this equipment, it should be protected against moisture penetration and corrosion. 

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. 

The overall intent of electrical area classification is to provide for safety of personnel and equipment. This is achieved by the elimination of electrical ignition sources near combustible gases or vapors that could explode or bum. The specific reasons for classifying facilities into electrical hazardous areas typically are ... 

Intrinsic safety is based on the principal of restricting the electrical energy available in hazardous area circuits such that any sparks or hot surfaces that may occur as a result of electrical faults are too weak to cause an ignition. The useful power is about 1 watt, which is sufficient for most current instrumentation. It also provides a personnel safety factor since the voltages are low and it can allow field equipment to be maintained and calibrated "live" without the need for a gas free environment verification. Electrical components or equipment can be manufacturer as intrinsically safe and there readily usable in areas where combustible gases or vapors may be present. 

Where facilities are exposed to the constant radiation of the sun, sun shades are provided over exterior exposed equipment that may not function properly at elevated temperatures or would deteriorate rapidly if left continual exposed to the direct sunlight. Most electrical or electronic equipment is rated for a maximum operating temperature of 40 °C (104 °F) unless otherwise specified, e.g., hazardous area lighting temperatures are normally specified for 40 °C (104 °F) limit. Of particular concern for fire protection systems are those containing storage for foam concentrates rubber hoses or other rubber components which may dry and crack. 

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... 

Hydrants and monitors should be spaced so that they can be safely utilized during a fire such that the total firefighting and equipment cooling water requirements for each fire area can be delivered. Hydrants are generally spaced a maximum of 200 ft (60 m) apart in process areas. Greater spacing is allowable in tank farms [up to 300 ft (91 m)] and low hazard areas, such as utility blocks. Hydrants and monitors should be located a minimum of 50 ft (15 m) from any equipment to be protected. 

Deluge protection can be applied over the entire hazard area with open sprinkler heads located at various floor levels or fixed water spray systems can be applied specifically on the equipment to be protected. Specific water spray application is preferred because it provides better equipment cooling and reduces the water wasted due to wind and fire draft. 

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. 

The procedure would typically include an inspection checklist, calibration procedure, test equipment stipulations, and documentation requirements (e.g., inspection certificates, calibration certificates, hazardous area certification, EMC/RFI certification, material certificates). 

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