IS & Ex


Ex-rated instruments for explosive atmospheres

March 2019 IS & Ex

In many industries, there are certain areas that are classified as hazardous or Ex areas. This is an area that contains, or may contain, combustible substances such as gas, vapour or dust. Typical hazardous areas include coal mines, grain silos, chemical and petroleum plants, offshore and onshore oil and gas rigs, oil refineries, pharmaceutical plants and paint shops.

During the coal mining process, byproducts in the form of coal dust and methane are produced. The build-up of either of these can be extremely dangerous. Even a tiny spark can set off a disastrous explosion. Similarly, grain silo dust ignited by a spark, has led to tragic explosions.

Safety measures in hazardous areas

In order for ignition to occur, two things are needed: the combustible atmosphere as described above, and a trigger i.e. a spark or flame. Remove one or both of these conditions and an explosion cannot occur.

Removing combustible dust and vapour

Ventilation equipment can dilute or remove dangerous substances from an enclosed area and as a result reduce the risk of explosion. This method is extensively used in the mining and chemical industry.

No trigger

Apart from ‘No Open Flame’ signs, precaution must be taken to prevent electrical equipment from being a source of ignition. A simple electrical switch, for example, can generate an electrical spark every time it is thrown – depending on the type of load. This spark may be enough to act as a trigger for an explosion in a hazardous area. In a similar fashion, sparks can be created by portable electronic devices. In order for devices to be safe for use in hazardous areas, safety precautions have to be built into the design.

Intrinsically safe (IS) instruments

There are several aspects in the design of IS electronic devices, of which reducing or eliminating switch sparking is but one. Other considerations include, fast fuses, controlling component temperatures, eliminating tight component spacing that could lead to a short circuit, and reducing circuit current and energy storage.

R&C Instrumentation is geared to supply a considerable range of intrinsically safe instruments, for instance the Raytek MT4-IS handheld non-contact thermometer for the temperature range -18 to 400°C, the Raytek Mi3-IS 4-wire system fixed pyrometer and the Raytek TX-IS 2-wire loop powered system fixed pyrometer.

As part of the recently launched range of vibration sensors, there is also a wide range of ATEX IEC and Ex certified versions available. Additionally, due to a special request from a mining client, there is now the UT390B+IS laser distance meter available from stock.

For more information contact R&C Instrumentation, +27 11 608 1551, [email protected], www.randci.co.za



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