Constructive Measures of Explosion Protection

Explosions can occur in process plants. They may endanger humans and the environment. If explosions cannot be prevented or rendered sufficiently improbable by measures of preventative explosion protection, constructive measures of explosion protection must be considered. They do not prevent explosions but offer protection. In particular we can apply [12]  

Furthermore, the propagation of the explosion pressure to adjacent parts of the plant must be prevented by explosion isolation or explosion suppression. 

Explosion-proof design implies that all structures potentially affected by an explosion can withstand the maximum pressure and the maximum pressure rise caused by a confined explosion. Details on confined explosions of flammable gases are found in Sect. 2.1.1.10 and of flammable dusts in Sect. 2.4.6. In considering this it must be kept in mind that the initial pressure of an explosion can be above atmospheric depending on process conditions. This leads to a corresponding increase of the maximum pressure. Explosion-proof design is an example for a passive safety measure. 

With explosion pressure relief the maximum possible explosion pressure is lowered by opening a relief vent after explosion initiation. This can be a bursting disc, explosion panel or explosion vent, with the latter allowing repeated use. In extreme cases the side wall or the roof of the industrial hall may serve as vent opening. By explosion relief the confined explosion becomes a partially confined one with a corresponding lower maximum pressure. Pertinent calculation procedures can be found in [12, 13]. 

In process plants apparatuses are connected by pipes. Therefore pressure waves generated by an explosion in an apparams can cause pressure loads in other apparatuses. In order to avoid this, isolation of apparatuses can be achieved by flame arresters (or other devices). They are described below following [14—16]. These impede the propagation of an explosion and hence reduce its consequences (level 4 of Table 4.1). They can be applied to mixtures of flammable gases or vapours with oxidants (usually the oxygen in air) or mixtures of dusts and oxidants. 

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A hazard analysis, for example a HAZOP study (vid. Sect. 9.1.2.3, serves to identify the necessary preventative or protective safety measures. Constructive measures of explosion protection are necessary if the occurrence of flammable atmospheres and sources of ignition cannot be totally avoided. 

When speaking about explosions, preventive and constructive measures are discriminated. This is also done in the case of protection against dust explosions. When discussing the preventive measures which have the task to eliminate the chance of a possible event actually occurring, the question of substance substitution is the first to be asked. If a dust explosible substance can be replaced by one which does not have this property, this substitution is the most effective measure. The probability that this exchange is possible in practice is, however, comparatively low. 

The chosen explosion protective measures must also remain effective during startup and shutdown of the plant, as well as during disturbances. If this goal can not be achieved by these preventive measures, then constructive measures are used, for example ... 

Tertiary or constructive explosion protection comprises structural and other measures by which the consequences of an explosion can be reduced. 

Primary measures are tending to eliminate hazard potentials or to protect from risks by using intrinsically safe measures of construction and design. Such risks could be the appearance of explosive atmospheres, pressure overload or overheating. In addition the primary measures reduce the preventive maintenance... 

If explosions cannot be excluded for sure, technical measures which limit the effects of an explosion to a harmless extent (no personal injuries, tolerable damages to property) (tertiary or constructive explosion protection). 

Containment (Explosion-Pressure-Resistant Design for Maximum Explosion Overpressure) An explosion-resistant construction is understood to mean the possibihty of designing vessels and equipment for the full maximum explosion ove (pressure, which is generally of the order P = 9 bar. The explosion-resistant vessel can then be designed as explosion pressure resistant or explosion pressure shock resistant. This protective measure is generally employed when small vessel volumes need to be protected, such as small filter units, fluidized-bed dryers, cyclones, rotaiy valves, or mill housings. 

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