A glimpse at the ongoing development of standards

The corresponding standard (IEC 60079-1) must be permanently revised to ensure the best possible testing of the enclosure properties for the Ex d type of protection in accordance with the state of the art. The NEXdGEN project will determine the influencing factors and their effect on material stress. The PTB is in charge of the project and is responsible for the design, execution and evaluation of the tests. We are providing test specimens and performing the same measurements at the R. STAHL laboratory. The tests will be evaluated jointly and the results will be incorporated in the next version of the standard.

One of the tests carried out as part of the NEXdGEN project is the determination of the reference pressure. Here, the maximum explosion pressure inside the Ex d enclosure is determined. For safety reasons, tests of this kind must be carried out in our Ex d test facility in our laboratory.

During the test, a specified explosive air-gas mixture is introduced into the test enclosure, ignited and the resulting pressure inside the enclosure is determined. Apart from an audible "click", which may vary in volume, nothing is heard here during the test. The determined maximum explosion pressure (reference pressure) serves as the basis for dimensioning the enclosure.

With regard to the Ex d type of protection, in addition to the test for the reference pressure, the test for non-transmission of an internal ignition is probably one of the most interesting tests in the laboratory. Here it is demonstrated that all joints in the enclosure safely prevent the propagation of the explosion to the outside. For this purpose, the same explosive gas mixture is introduced into the Ex d enclosure and into the direct vicinity of the enclosure – i.e. into the test boiler – during the test. If the gas mixture inside the test enclosure is ignited and the surrounding gas mixture is not ignited, the enclosure is flameproof.

In order to cause ignition transmission, we deliberately expand a joint in an Ex d enclosure. The joint width of the plane joint between the enclosure and cover is chosen so that it is large enough to ensure that the internal explosion is propagated to the outside. This illustrates the effect on a potentially explosive environment outside the enclosure. This explosion generates a loud bang.

Images of the course of an explosion from the inside of the Ex d enclosure into the interior of the test facility, taken using a high-speed camera that takes 1000 images per second: