Intrinsically safe systems

ISA RP 12.6. 1987. Installation of Intrinsically Safe Systems for Hazardous (Classified) Locations. (ANSI approved.) Instrument Society of America, Research Triangle Park, N.C. 

The mere fact that voltage, current, or even both, are at low levels does not guarantee a circuit to be intrinsically safe, even though intrinsically safe circuits do utilize relatively low voltage and current levels. Intrinsically safe systems employ electrical barriers to assure that the system remains intrinsically safe. The barriers limit the voltage and current combinations so as not to present an ignition hazard should a malfunction develop. Typically, devices upstream of barriers are not intrinsically safe and are installed in control rooms or other unclassified locations. All devices and wiring on the downstream side of the barriers are intrinsically safe and can be installed in classified areas. 

An additional benefit of intrinsically safe systems is the reduction of electrical shock hazards. It is cautioned, however, that intrinsically safe systems are not necessarily tested specifically for personnel shock hazards. 

Circuit capacitance and inductance, including the values of these parameters for interconnecting wiring, are integral parts of the overall analysis. It is not always possible to assure that the system will be maintained as designed with only approved intrinsically safe components and with circuits of the capacitance and inductance as originally installed. For this reason, intrinsically safe systems are used primarily at locations where there are sufficiently trained personnel to assure that the intrinsic safety of the system is always maintained. 

Optical fiber cables and fiber optic devices approved as an intrinsically safe system suitable for the hazardous (classified) location involved shall be installed in accordance with Sections 504-20 and 770-52. 

Intrinsically Safe Systems. Intrinsically safe apparatus and wiring shall be permitted in any hazardous (classified) location for which it is approved, and the same provisions of Articles 501 through 503, 505, and 510 through 516 shall not be considered applicable to such installations, except as required by Article 504. 

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. 

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. 

Certificates are issued not only for individual apparatus. In the same way, an intrinsically safe system e.g. composed of a sensor, cable, power supply and meter amplifier, can be certified. This practice is customary in the Anglo-Saxon countries (United Kingdom, USA). Here, only those apparatus shall be planned and fitted which are listed or specified in the system certificate. So, a high level of safety results for the planner and user since the intrinsically safe system in its entirety (including all components) has been examined. When, however, another component has to be fitted, e.g. due to the nonavailability of a specified device, the system shall be certified again (see Section 6.9.6). 

In certification practice, the so-called intrinsically safe systems are known as well. Deviating from a (single) apparatus which is certified individually, an interconnection of several apparatus is under consideration for an intrinsically safe system, including the connecting cables for the most part. Several intrinsically safe circuits and different categories of these circuits as a part of an intrinsically safe system are permissible. 

In addition, it may be mentioned as a special feature of intrinsically safe systems that a fault analysis (as an assessment for individual apparatus) (two faults are assumed for category ia, one fault for category ib) may be applied to the system as a total and not to each individual apparatus. 

A separate chapter of standard EN 50039 is dedicated to cables in an intrinsically safe system. Special requirements for multicore cables with several intrinsically safe circuits are listed as well as the faults to be assumed between intrinsically safe circuits (wire breaks and short-circuits) if these requirements are not met. In the meantime, these requirements form a part of standards EN 60079-14 and IEC 60079-14 respectively (see Section 6.9.5). 

In applications where a transfer rate increasing year by year is to be expected with investments step by step, the electrical solution with an intrinsically safe data transmission may be favourable. The optical data transmission system shows investment costs copt/ as a total in the first year, and the intrinsically safe system investment costs c, in the year number i (i = 1,... n). So, the total costs are copt for the optical system and ... 

Your wiring needs to meet the code requirements of your AHJ. For IS (intrinsically safe) systems, normal wiring is usually considered appropriate, but it is sometimes required that the wire be either thicker or have special insulation. Check the code for your area. 

Low-level input sensors such as thermocouples, turbine meters, speed transmitters and a number of process analyzers complicate system selection. Signal conditioning equipment is required for low-level inputs to both the back-up system and computer data acquisition systems. If the system is to be installed as an intrinsically safe system, multiple grounding requirements conforming to intrinsic safety grounding must be referenced to the same safety ground to avoid multiple ground problems. 

Cables that must function as long as possible in safety control systems e.g., fire and gas detection systems, ventilation damper control and power systems, UPS, public address and communication systems, intrinsically safe systems. 

VAC-U-MAX Compressed-Air Powered Vacuums, are the first-line offerings for Class II, Division 2 environments due to their bumper-to-bumper grounded and bonded design and their reasonable cost and availability. These vacuums meet the NFPA 77 and 654 requirements for grounding and bonding. These vacuums also meet the definition of an intrinsically-safe system". VAC-U-MAX air-powered vacuums do not use electricity and do not generate any heat from operation. 

An intrinsically safe system, suitable for use in zone 0, is one in which all the equipment, apparatus and interconnecting wires and circuits are intrinsically safe. 

In an intrinsically safe system, all possible equipment is designed and installed in such a way that it does not have enough energy to cause ignition of the potentially explosive gas mixture, even in a fault (spark) condition. One uses low-power devices, such as those powered by 24 VDC. Nearly all sensors are available as intrinsically safe models. 

A) Developed based on idea from MTL Surge Technologies — surge protection for intrinsically safe systems MTL... 

RP12.6 Installation of Intrinsically Safe Systems for Hazardous (Classified) Locations. 

Intrinsically safe A term applied to the installation of electrical devices in an explosion hazard area. An. intrinsically safe system is one designed, in-st ed, and maintained so that imder the most adverse conditions it cannot produce an arc of sufficient energy to be considered a source of ignition. 

There are relatively few, if any, intrinsically safe systems, although some systems fall into this class if we ignore misuse. In most cases of interest we have to engineer systems to achieve acceptable levels of safety. This is intrinsically risk-related as a system is more acceptable the lower the level of risk, although acceptability is often influenced by the benefit of using the system, so the analysis is not straightforward. The development process and assessment (safety analysis) is driven by the risks and the design of mechanisms to combat the risks. 

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