Explosion protection intrinsic safety

Classification and marking of intrinsically safe apparatus concerning explosion groups (I, IIA, IIB, IIC) and temperature classes (T1-T6) are organized in the same way as for, e.g., flameproof enclosure - d (see Tables 4.1 and 4.2, Chapter 4, and Chapter 5 for marking). Some special features, however, which are of importance for type of protection intrinsic safety - i only, will be explained in the following. 

Transmitters are used to record different physical quantities, e.g. temperature, presssure, flow, level, pH value and so on. The mechanical design corresponds to requirements at the place of duty. Due to the small power demand, type of protection intrinsic safety - i is an obvious choice in the field of explosion protection in most cases. 

The term intrinsic has a meaning similar to that of inherent, but the common usage of intrinsic in the chemical industry usually means a protection technique related to electricity. Intrinsic safety is based on the restriction of electrical energy to a level below which sparking or heating effects cannot ignite an explosive atmosphere (Lees,2 p. 513). 

Only in the field of data transmission, communications, remote controlling and monitoring, has the very small energy amount, when switching electric circuits, formed a very useful basis for a special type of explosion protection, the so-called intrinsic safety as given in IEC 60079-11 and EN 50020. 

In the history of explosion protection of electrical apparatus, remote monitoring and controlling has become more and more the domain of intrinsic safety - i... 

In principle, intrinsically safe apparatus do not need an enclosure since explosion protection is inherent due to the design of the circuitry. In cases where intrinsic safety - i - may be adversely affected by any access to live parts (e.g. infallible creepage distances in air), an enclosure ensuring an IP code of (at least) IP 20 (according to IEC 60529) shall be fitted. 

In most cases, an intrinsically safe circuit is put into practice so that a safety barrier or an Ex i-isolator or an Ex i-input/output is connected to measuring devices or positioning elements (sensors, actuators) located in a hazardous area via a cable (see Fig. 6.217). Hence, explosion protection cannot be purchased ready for use for the most part, but it has to be put into practice by the planner and electrician. Only in cases where apparatus and cables are... 

An assessment for certification can be performed on the basis of simulations only, due to the complexity of the relations pointed out above. The software developed for it enables qualified statements concerning the power distribution on cables including bus connections. Here, concerns of explosion protection are taken into account. The aim of these investigations is a statement valid in general for the intrinsic safety at different bus configurations. 

Intrinsic safety combined with other types of explosion protection... 

Safety equipment and interface Fire/explosion with detection and protection, chemical reactivity, mitigation system, enclosure class, intrinsic safety circuits, etc. 

A protection technique based upon the restriction of electrical energy within the apparatus and in the interconnecting wiring, exposed to an explosive atmosphere, to a level below that which can cause ignition by either sparking or heating effects. Because of the method by which intrinsic safety is achieved it is necessary that not only the electrical apparatus exposed to the explosive atmosphere, but also other (associated) electrical apparatus with which It Is Interconnected, Is suitably constructed. 

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