Intrinsic safety installation

To comply with the requirement of intrinsic safety, all electrical circuits installed at such locations should be safe and must produce no spark or heat under normal or lault conditions, sufficient to cau.se ignition of the surroLindittg medittm. The paratneters of the circuit such as V. /, R. L. and C, which can release heal energies by... 

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. 

As a rule, this Ex i-isolator is installed in a safe area and connected to additional apparatus not ex-protected, e.g. to a single loop controller or to a PLC (Programmable Logic Controller). Therefore, in the field of intrinsic safety two types of apparatus are distinguished ... 

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 mentioned above, the main domain of application of intrinsic safety is remote control and monitoring instrumentation. More than two million intrinsically safe circuits for sensors and actuators alone are installed anew or modernized year by year. 

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 ... 

Again and again, testing houses, manufacturers and users of intrinsically safe products have put the question, how could the narrow borderlines of classic intrinsic safety concerning available power be passed over These borderlines are determined by reference curves as well as by installation rules. The following approaches are dealt with in more detail below ... 

In the example of Fig. 6.233 a power supply for installation in zone 1 is protected according to flameproof enclosure - d The outputs (max. four) to supply the other system modules comply with intrinsic safety - i - with maximum values as follows ... 

A system specified to such a degree is intrinsically safe with a maximum of 32 field devices and two terminations. The proof of intrinsic safety is thereby reduced to a list of the apparatus installed and their certificate. The marking includes FISCO and the type of apparatus, e.g. power supply, field device, termination. 

In the field, the topic of process control includes the selection and installation of sensors, transmitters, transducers, actuators, valve positioners, valves, variable-speed drives, switches and relays, as well as their air supply, wiring, power, grounding, calibration, signal conditioning, bus architecture, communications protocol, area classification, intrinsic safety, wired interlocks, maintenance, troubleshooting, and asset management. 

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. 

Items in seismic category 2 should follow the practice for design, installation and maintenance for nuclear applications. However, in the hypothesis in para. 2.18 (b) (interacting items), lower intrinsic safety margins than those specified in nuclear standards can be applied when the probability of interaction with items in seismic category 1 or 3 is considered very low. 

LG. Kegel, Foundation Fieldbus topologies for intrinsic safety (IS) installations, in Foundation Fieldbus End User Council Meeting Middle East, Pepperl+Fuchs GmbH, Maltaqa, 2007. 

Intrinsic Safety. Division I areas can also use intrinsically safe barriers to provide an "explosion-proof" installation. These barriers must be located and connected in accordance with the rules for intrinsically safe installations, such as ISA RP12.6. 

Since integrity is required for EE-C2 items and only limited (or, in some cases, no) functionality is required to prevent their interaction with Category 1 items, more simplified and less conservative criteria for design, installation and maintenance may be used, in some cases with a lower intrinsic safety margin than for EE-Cl items, in relation to their probability of being the initiator of an... 

The signaling relay (intrinsic safety) is controlled through a power supply galvanically isolated from the rest of the installation. This insulation helps to reduce the risk of wrongly recharging and activating in the case of a cable mpture. 

First, once designed, evaluated, and installed, the safety of the system cannot easily be degraded because the safety is in the design, not protection added afterward. In fact, the intrinsically safe electrical circuit will cease to fulfill the function for which it was designed long before it can become a hazard. This is due to the consideration which must be given to fault conditions. The only possible way for the circuit to become hazardous is if an unapproved or unauthorized component is substituted into the circuit. 

Computer hardware will require electrical earths and signal earths for intrinsic and nonintrinsic safety to be achieved. Wiring diagrams should be available as appropriate to site-specific installations. 

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. 

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