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Inherently safe despite higher pressure

In current investigations at PTB the concept of intrinsically safe has been expanded to higher temperatures and pressures. As a result chemical industries can utilize electrical devices certified for operation in higher than atmospheric ambient conditions in the future.

In such a spark-test apparatus device tungsten wires scratch along a rotating cadmium disc and produce electrical sparks – until an explosion is ignited in the surrounding gaseous mixture.

An electrical device is termed or intrinsically safe if it is impossible to ignite an explosion with the device despite the possibility of electrical sparks. In this regard intrinsically safe means the possible maximum energy in an electrical circuit is limited so that occurring sparks are not provided with enough energy to ignite an explosive mixture of flammable gases and air. Such gaseous mixtures are very customary in chemical and petrochemical industries.

Minimum ignition curves are crucial to the attribute intrinsically safe. Such curves mark the temperatures and ambient conditions at which an ignition probability of 10-3 is established. In this context PTB has investigated the ignition behaviour of electrical sparks and the resulting explosions at higher temperatures and pressures. The relevant limiting curves for different gaseous mixtures have been determined with a spark-test apparatus device at ambient conditions at atmosphere and above. With the obtained results PTB can now test and legally certify intrinsically safe devices for temperatures up to 100 °C and pressures up to 5 bar.

The advantages for producers of electrical devices and subsequently for the chemical industry are unequivocal: producers could not guarantee the safe operation of their devices beyond the certified range and – in case the devices were deployed at all – the chemical industry was forced to take the liability at their own risk. The new results on inherent safety by PTB relieve the chemical industry from this risk burden.

Contact at PTB:

Phone: +49-531-592-0