Hazardous area installations

Electrical installations in hazardous areas (other than mines)... 

Electrical apparatus for explosive gas atmospheres. Electrical installations in hazardous areas (other than mines) 5571/1991 BS EN 60079-14/1997 ... 

Since it is not practical to manufacture a llameproof enclosure due to its size and bulk and the number of knockouts and openings on the doors for switches, metering, indicators, and pushbuttons (PBs) etc., it is common practice to locate the.se assemblies some distance from the affected area in a separate well-ventilated room. Depending upon the location and intensity ol contamination, it may be permissible to meet the requirement by using a pressurized enclosure by maintaining a positive pressure inside the enclosure similar to that for motors (Section 7.1.3..3). When there arc many switchgear assemblies, the room itself can be pressurized, which is safer and easier. Small enclosures, however, such as a PB station, switch or a switch fuse unit or an individual starter unit etc., which can be easily made of MS plates or cast iron, as discussed in Section 7.13, can be mounted in the hazardous area while the main MCC can be installed in the control room, away from the contaminated area and from where the process can be monitored. 

Today loading piers are mostly cathodically protected with impressed current. At moorings for tankers, cathodic protection rectifiers are installed on extinguisher bridges as far as possible from the hazardous area. Otherwise, they must be of an explosion-proof type. 

AMD 1 Electrical apparatus for explosive gas atmospheres. Electncal installations in hazardous areas (other than minesj. Comgendum No. 1 (Corr. 10013J dated April 1998, superseded BS 5345 Part 1 1989, Parts 2 and 7 1979, Part 4 1977, Part 5 1983, Part 6 1978 and Part 8 1980... 

LIMITATIONS ON INSTALLATION OF ELECTRICAL DEVICES IN HAZARDOUS AREAS... 

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. 

MacMillan, A. (1998) Electrical Installations in Hazardous Areas (Butterworth-Heinemann)... 

In instances where CO2 storage bottles are installed in enclosed spaces, an exhaust fan is usually provided the protected hazard area. It is activated to remove the vapors once a system has been fully discharged, rather than a prevention measure for partial vapor release and disposal of unexpected leakages. 

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... 

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. 

Where it is possible for flammable or toxic gas or vapor released within a hazardous area to migrate to the inlets for HVAC systems serving nonhazardous enclosed areas such as control rooms, detection systems should be installed in those HVAC inlets or connecting ductwork. Detection should be provided in HVAC system intakes if the building, room, or enclosure served is not electrically classified and a flammable (or toxic) gas or vapor could feasibly be drawn into the area, either by mechanical ventilation systems or by differential pressures. The detection system should alarm and automatically shutdown the HVAC to prevent gas or vapor concentration in the protected space from reaching the flammable or toxic range. 

The oscillation amplitude is too small (typically, 100 pm) to cause damage to the meter. Because the excitation current is also very small, intrinsically safe CMF versions are available for use in hazardous areas. The electronics can be mounted on the flowmeter directly, forming one compact unit, or the flowmeter can be interfaced to the electronics via a cable. The remote assembly may be necessary for high-temperature meters, or it may be convenient if the sensor is installed in a place that is not easily accessible. 

This approach is practical only when the release point is predictable, for example, at a vent pipe or pump seal, as the plate must be installed before a release occurs. Furthermore, the release must be carefully modeled to ensure that a smaller hazard area will result. 

Installation rules for hazardous areas are given in international standards, IEC 60079-14 (1996-12), subsequent in EN 60079-14 (1997-08), and have been transformed into the German Standard VDE 0165 Teil 1 (1998-08), covering zones 0,1 and 2. The basic ideas for the installations in zone 2 are ... 

If the apparatus with intrinsically safe circuits is installed outside a hazardous area, e.g. in a control room in a chemical plant, the marking inserts Ex or EEx and the type of protection in brackets ... 

Apart from inserting the complete gas analyser into a p-enclosure, the analyser head may be explosion protected for zone 1 application (e.g. according to flameproof enclosure - d - ) on its own, whereas the central control unit may be installed in a non-hazardous area, or alternatively, in a pressurized enclosure (Fig. 6.25) when zone 1 installation is required. 

The installation of generators in hazardous areas is focused on special applications. The specific advantages of pressurization as demonstrated for motors apply in full for generators. Two examples shall be given ... 

The monitoring unit shall be installed in a non-hazardous area). 

Type of protection for the monitoring unit, to be installed in a non-hazardous area [EEx ib] MB... 

Associated apparatus is commonly installed in a safe area. Many applications of intrinsic safety in remote control and monitoring instrumentation are assembled in such a way that an intrinsically safe apparatus, e.g. a sensor or actuator in the hazardous area, is connected with an associated apparatus, e.g. a safety barrier or an Ex i-isolator in the safe area (see Fig. 6.196). With that, the associated apparatus takes over the function to safely limit current and voltage in the intrinsically safe circuit to permissible values. 

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. 

Currently, remote I/O systems of several manufacturers are available for operation in zone 1 or Division 1. To a large extent, these systems are based upon the technology of intrinsic safety. The power supply only is designed according to another type of protection, e.g. flameproof enclosure - d A remote I/O suitable for hazardous areas may be an integration of input (I) and output (O) assembly units of automation systems and of Ex i-isolators of classic design. The installation may be made in a hazardous area and supersede the classic field distribution box (terminal box). Standardized fieldbus systems may be used for data transmission from/to the automation system. These remote I/O systems for hazardous areas are characterized as follows ... 

Figure 6.231 A fieldbus is designed according to explosion Group IIB. To extend it with field devices into a hazardous area endangered by Group IIC gases, an additional current limitation is installed in the terminal box.

Optoelectronic components for remote control and monitoring and for data transmission are being installed in hazardous areas more and more. In particular, the optical-fibre transmission technique enables numerous modem applications. Apart from the great advantages of this technology, the risk of an ignition caused by optical radiation at a power level sufficiently high is to be taken into account (see Section 1.2.7). 

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