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hes april 18 17Explosion Safety

Everything you need to know about how an explosion arise and how to protect your plant

An explosion is based on the availability of oxygen from the air, a source of ignition and a combustible substance. In the event of a dust explosion, the distribution of dust is another factor.

However, not every dust-air mixture is explosive. What matters is the mixing ratio. Specific explosion limits have been identified for every common type of dust, and within those limits you can expect an explosive mixing ratio. (Read More)

 

The lower explosion limit is the minimum concentration required to create an explosive atmosphere. The upper explosion limit specifies the point from which the mix is too rich, so that the atmosphere is no longer explosive.

There also needs to be an effective source of ignition: “An effective source of ignition is one where the relevant explosive atmosphere can cause an explosion.”

[TRBS 2152 Part 3, “Hazardous explosive atmosphere – avoiding the ignition of a hazardous explosive atmosphere”, page 2]

Common sources of ignition are hot surfaces, electric sparks and glowing embers, created in the process.  

Explosion safety precautions

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 an explosion protection. Preventive precautions are designed to prevent an explosive atmosphere and therefore to reduce the probability of an explosion. Wherever this is possible, combustible substances are replaced by substances that cannot produce an explosive mix. In addition, it is possible to overlay the substance-air mix with inert gases. This has the effect of lowering the content of oxygen from the air, so that no explosion can occur.

Additionally, preventive precautions concentrate on the avoidance of effective sources of ignition. This includes, for instance, the use of suitable equipment, protecting the product flow from impurities and monitoring the earthing of the system with a view to preventing electronic discharge.

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:

Flameless 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. This problem is often solved through the use of vent ducts, which channel the spread of an explosion to the outside. The disadvantage, however, is that it prevents any process-optimised plant design and is usually very expensive: the longer the distance between an explosion and its source, the higher the pressure which the vent duct and the plant need to withstand. This results in higher (production) costs for the vent duct.

Flameless venting, on the other hand, is an option that is both economical and effective. Different manufacturers use different technologies in flameless venting.

Let us have a look at one particular technology at this point: The special mesh filter that is used in a Q-Box or Q-Rohr efficiently cools down any flames, preventing both flames and pressure from emerging and ensures particulate retention. The typical increase in pressure and noise that accompanies an explosion within a building is reduced to an almost imperceptible minimum, thus protecting both humans and machinery. In addition to the special stainless steel mesh filter, the Q-Rohr and Q-Box each have an explosion vent with an integrated signalling system that alerts the process control system when the explosion vent has opened.

For more information visit:
www.rembe.com