Investigations of static and dynamic stresses of flameproof enclosures

Flameproof enclosures house electrical equipment used in hazardous areas. To assess the ability of an enclosure to withstand pressure, a test - which is defined in IEC 60079-1 (2014) for the type of protection flameproof enclosures - has to be performed. Based on the maximum pressure measured after igniting explosive gas mixtures inside the enclosure, either a hydrostatic or a dynamic overpressure test has to be performed to verify the mechanical strength of the enclosure. Both tests are considered satisfactory if no permanent deformation or damage invalidating the type of protection can be detected. In this work, these two different test methods are compared and evaluated. The results show that the static and dynamic stress, and thus the two different test methods, cannot be considered equivalent. Especially in case of insufficient damping of the mechanical load, or if this load corresponds to the natural frequency of the enclosure, the dynamic stress is much more critical.