The most important explosion safety systems at a glance
12 February 2021
Which protective system is the right one for my application? Depending on the results of the hazard and risk analysis, a number of proven precautions need to be taken. They are divided into explosion prevention and explosion protection.
Preventive precautions are designed to prevent an explosive atmosphere and therefore to reduce the probability of an explosion.
Protective precautions involve reducing the impact of a possible explosion to a more moderate level, so that the resulting damage is less severe. This includes conventional venting through the use of explosion vents, flameless venting, explosion isolation and explosion suppression. This kind of explosion safety is a vital necessity in virtually all plants, because...
• it is in the nature of the relevant processes that there can almost never be any absolute or complete avoidance of effective sources of ignition,
• inerting tends to be too expensive and/or impossible due to the nature of the processes involved. Other preventive precautions may be helpful in parts, but cannot usually eliminate the risk of an explosion completely.
As protective precautions are of such high relevance, we shall briefly outline the most common safety systems at this point:
Conventional venting through the use of explosion vents
If a plant is situated outside buildings or if parts of a plant are next to an outer wall, one frequent safety precaution is to install explosion vents. Such precautions are usually applied, for instance, to stationary silos, filters and elevators situated outside of buildings. If an explosion occurs, the explosion vent protects the system by opening. This reduces any overpressure within the vessel, and the explosion is released to the outside. As virtually no processes are the same, there are numerous types of explosion vents which differ in shape and material and also in their resistance to temperature, pressure and vacuum. Even processes with considerable hygiene requirements can be equipped with explosion vents today.
Flameless explosion venting
If a plant is situated within a building, however, explosion vents are not suitable for pressure relief purposes, as the safety area around them is inadequate to relieve the emerging dust and flames. Such an arrangement would pose an enormous safety risk to humans and machinery.
Flameless venting is a solution that is both economical and effective. Different manufacturers use different technologies in flameless venting.
In a production facility the individual parts of the plant are always connected by pipelines. The purpose of explosion isolation is to ensure that the pressure and the flames cannot propagate and so that any adjoining parts of the plant are protected. A distinction is made between active and passive isolation systems.
An active system is alerted to an explosion at an early stage, when an explosion begins to develop. This is done through sensors or detectors which register the rise in pressure or the formation of flames and respond by activating the relevant isolator, e.g. a quench valve.
Passive isolation, on the other hand, responds purely mechanically to the spreading or loss of pressure, on account of its structural characteristics. This also applies to explosion valves.
In addition to the methods mentioned so far, another constructional precaution is explosion suppression. It means eliminating the explosion at its very onset. This is made possible by detectors which register the presence of sparks or flames through sensors and immediately trigger the opening of tanks containing an extinguishing agent (also installed in the system). A highly effective extinguishing agent is released within milliseconds, nipping the explosion in the bud straight away. If required, an explosion suppression system can also be used for explosion isolation purposes.
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