Intrinsically safe equipment electrical

Intrinsically Safe Equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture or hazardous layer. 

Availability. Both Underwriters Labatories and Factory Mutual Research publish yearly guides to electrical equipment which they have certified and continue to certify as being rated for use in hazardous environments. Many of the items contained in these guides are rated as intrinsically safe or as associated equipment for use with intrinsically safe equipment. Further, the amount of equipment available should increase each year as the demand increases for intrinsically safe electrical circuits. 

Intrinsically-safe equipment is designed to be incapable of releasing electrical or thermal energy that would ignite a hazardous atmospheric mixture. 

Intrinsically safe equipment approved for use in the European community might not pass UL 913 tests for intrinsically safe designation in the U.S. The standards are similar, but not identical. Integration components intended for different codes or systems should be avoided, unless approved by an appropriately qualified electrical engineer. 

When volatile flammable materials may be present, use only intrinsically safe nonsparking electrical equipment, which is not liable to overheat. 

EN 50039 Intrinsically safe 1st electrical systems i Part B Electrostatic spraying equipment 1980-03 1st VDE 0170/ 0171 Teil 10 1982-04... 

Ordinary electrical equipment cannot be installed in zone 0, even when it is flameproof protected. However, many chemical and oil-processing plants are entirely dependent upon instrumentation and data transmission for their safe operation. Therefore, very low-power instrumentation and data-transmission circuits can be used in special circumstances, but the equipment must be intrinsically safe, and used in conjunction with a safety barrier installed outside the hazardous area. Intrinsically safe equipment must be marked Ex ia or Ex s , specially certified for use in zone 0. 

In a circuit where the amount of electrical energy available to cause a spark is below that necessary for igniting flammable vapour or gas, the equipment is considered to be intrinsically safe. It is particularly suitable for use in instrumentation, remote control etc. Intrinsically safe equipment to category IA may be used in any Zone except that in which there are contacts that could spark. It should not be used in Zone 0. Category IB equipment may be used in all zones except Zone 0, See BS5958 . ... 

Any experienced maintenance organization can coordinate the replacement of conventional electrical equipment with intrinsically safe equipment. 

ISA R12-6 defines IS as A type of protection in which a portion of the electrical system contains only intrinsically safe equipment (apparatus, circuits, and wiring) that is incapable of causing ignition in the surrounding atmosphere (ref Clause 3.12 of ANSI/ISA RP12.06.01 2003)... 

Intrinsic Safety. Static electrical concepts such as minimum ignition energy do not directly apply when assessing the safety of electrical circuits such as radios, flashlights and instmmentation. Intrinsically safe electrical equipment is usually available which has been subjected to fault analysis and testing. The equipment must be certified for the flammable atmosphere in which it will be used (NFPA 497). Refer to texts on Intrinsic Safety such as [63]. 

Std. 3615 Explosion-proof Electrical Equipment Std. 3610 Electrical Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous Locations... 

The use of intrinsically safe electrical and instrumentation equipment in appropriately designed environments can guard against many electrically related discharges. Reference should be made to authoritative books on this subject. 

FPN No. 3) ft is not good practice to install electrical equipment in Zone 0 locations except when the equipment is essential to the process or when other locations are not feasible. (See Section 500-2.) If it is necessary to install electrical systems in Zone 0 locations, it is good practice to install intrinsically safe systems as described by Article 504. 

Processes can be divided into those that are intrinsically safe, and those for which the safety has to be engineered in. An intrinsically safe process is one in which safe operation is inherent in the nature of the process a process which causes no danger, or negligible danger, under all foreseeable circumstances (all possible deviations from the design operating conditions). The term inherently safe is often preferred to intrinsically safe, to avoid confusion with the narrower use of the term intrinsically safe as applied to electrical equipment (see Section 9.3.4). 

In 1938, the United States Bureau of Mines began development of rules relating to the use of electricity for telephone and signaling equipment, which included application of intrinsically safe electrical circuits. 

Until the 1950 s, the use of intrinsically safe electrical circuits had little application in other than just battery operated signaling devices. At this time due to advances in technology and an increase in the use of electrical equipment in hazardous locations, a new world-wide interest developed in the application of intrinsically safe electrical circuits beyond what had been its traditional role. 

The first task, which should be completed before considering the design of any facility or equipment involving energetic material, is to define exactly what type of hazardous environment will be involved in each room, section or area. This is a prerequisite, whether selecting intrinsically safe or any other technique to provide electrical protection. 

Due to the concept of low energy, intrinsically safe electrical circuits do not provide the energy necessary to drive motors or high powered electrical equipment. Nevertheless, this does not limit or restrict their application in the real world. 

The U.S. Army Defense Ammunition Center and School is employing the use of intrinsically safe electrical circuits in equipment designed to demilitarize and renovate munitions - from small arms to large projectiles. This is accomplished by using pneumatics and hydraulics to provide the power, while using position switches and solenoid valves linked to programmable controllers to direct the total machine process. 

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. 

Fine Print Note No. 2 in the Code states where ignitable concentrations of flammable gases (vapors) can exist continually or for long periods of time, electrical equipment should be avoided altogether, or, intrinsically safe systems should be used. 

Another kind of electrical equipment suitable for use in hazardous locations is equipment whose maximum possible energy output is insufficient to ignite the hazardous material. The electrical input to this equipment must be controlled by a specially designed electrical barrier. Such electrical equipment must be compatible. ANSI/UL913 defines low energy intrinsically safe electrical equipment and associated apparatus permitted in Division 1 areas. Nonincendive electrical equipment is permitted in Division 2 locations. Table 7-6 describes intrinsically safe and nonincendive equipment and identifies permitted uses. 

Acceptable protection techniques for electrical and electronic valve accessories used in specific class and division locations include explosion-proof enclosures intrinsically safe circuits nonincendive circuits, equipment, and components dust-ignition-proof enclosures dusttight enclosures purged and pressurized enclosures oil immersion for current-interrupting contacts and hermetically sealed equipment. Details of these techniques can be found in the National Electrical Code Handbook, available from the National Fire Protection Association. 

The description of the different types of protection in Chapter 6 indicates that there are two very different ways to solve this problem - if an electrical transmission is required at all. One way is to use intrinsically safe circuits, the other one applies industrial equipment as usual, additionally explosion protected by an enclosure as appropriate, e.g. flameproof housings for smallsized devices. In the history of process instrumentation, the appearance of semiconductors and integrated circuits has drastically reduced the power consumption of field devices. So, intrinsically safe circuits dominate this field today. 

Various protection techniques can be used to prevent electrical equipment from becoming an ignition source. Explosion-proof enclosures, pressurized and purged equipment, and intrinsically safe circuits can be used in Division 1 and Division 2 locations. Nonsparking equipment can be used in Division 2 locations. Details of the types of equipment permitted in each classified location are given in NFPA 70. 

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