The basics of dust-explosion protection - STAHL - #13

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4.3 Constructional Explosion Protection

Constructional explosion protection is a method of avoiding the hazardous effects of explosions and/or of limiting the effects of an explosion to a safe level by the use of:

> Explosion-resistant design limits an explosion to the inside of pressure-resistant vessels or pressure-shockresistant vessels -which, however, also means that connected equipment such as tubes/pipes and decoupling measures must meet the same conditions. Explosion-pressure resistant vessels or apparatus are those that can withstand many times the expected explosion pressure without being permanently deformed. Explosion-pressure shockresistant vessels or apparatus are constructed so that they can withstand the expected explosion pressure without breaking; however, permanent defor­mations may be a result. In this case, then, the robustness of the material may be brought closer to its limits.

> Explosion relief (defined pressure relief by means of bursting discs, venting panels or explosion doors, etc.) This measure is intended to prevent the build-up of excessively high explosion pressure in the interior of vessels by the timely release through defined openings. This measure addresses only the effects of the explosion, and can be implemented without additional control mechanisms. As soon as the static response ejection process from the protected apparatus into the surrounding area begins. Apart from the flame and shock wave,

this ejection process from the relief apertures associated with the explosion pressure relief also contains burnt and unburnt combustible substances. It must always be checked whether the consequences of the explosion in the loca­tion in question can be controlled.

Explosion suppression This process is generally used in vessels and production equipment for which an explosion pressure exceeding the explosion pressure resistance of the system in question is predicted. The explosion is suppressed in its initial stages, before a hazardous rise in pressure can take place. To accomplish this, an extinguishing agent is used in the protected area within fractions of a second of the explosion being detected. For the suppression of an explosion (use of extinguishing agent) it is mandatory that the explosion be detected promptly. In the case of explosions that begin slowly, the initial pressure rise is not sufficient for its timely identification. Additional measures such as optical flame detectors or supplementary pressure detectors may be necessary.

Explosion barriers (prevention of explosion propagation, explosion decoupling). Isolation as an explosion protection measure allows the explosion to reach full force, but prevents it from propagation into other, unpro­tected parts of the system. This is accomplished by mechanical barriers which immediately block connecting routes, or by a chemical ex­tinguishing barrier.

R.STAHL Explosion protection