Mistakes in flameless explosion protection can lead to danger and damage, explains Tomáš Wyka.
The first thing to know is that flameless venting is not regular explosion venting. Explosion venting is a favourite method in the explosion protection market. Why? Its function is simple, effective and it’s easy to install and replace. A pressure-sensitive membrane installed on protected technology opens in the event of an explosion. Flame, heat and pressure are released outside to the safety zone and technology is protected. So, what exactly is flameless venting? Flameless explosion venting is a safety measure used in industrial settings to mitigate the risks associated with dust explosions. It involves the controlled release of pressure, flame, and heat from an explosion without allowing flames or burning materials to escape and cause secondary fires or further damage.
Flameless devices are used to facilitate controlled explosion venting in scenarios where the presence of flames and the force generated during explosion venting could pose risks to personnel and infrastructure. The difference between traditional explosion venting and flameless venting is one extra part. The venting panel is equipped with a flame-quenching device to avoid transmitting flames into the surroundings.
So, will I get a flameless venting device if I add a flame-quenching element to my existing explosion venting device? The answer is resolutely no.
Two separate devices
Explosion venting devices and flameless explosion venting devices are two separate protection devices with specific norms, regulations and certification. European norm EN 16009 recognises several flame-quenching elements, such as ribbon, parallel plates, ceramic or mesh/gauze type. The mesh or gauze flame quenching element is one of the most used safety devices in various applications to prevent flame and heat transmission. It consists of multiple layers of mesh material with varying wire diameter and mesh size.
When a deflagration (rapid combustion) event occurs in an enclosed space, pressure and heat build up. The venting device releases this pressure and heat into the flame quenching element. The large wire surface area of the mesh allows for efficient heat absorption. The absorbed heat is dissipated throughout the mesh, effectively cooling it down below the ignition temperature. By keeping the temperature of the mesh below the ignition point, the flame cannot propagate through the mesh.
Know what you are working with
If you are considering flameless venting devices or any other explosion protection device in general, you must know your dust, your material and its explosion characteristics. That is the alfa and omega to any well-designed explosion protection. For the successful application of flameless venting, the heat of combustion of the material is an important parameter because it determines the amount of heat produced during the combustion of that material. There is a difference between heat from organic dusts and metal. If the heat of combustion is too high, the amount of heat transferred will not be sufficient to provide flameless venting, and flame extinguishment will not be successful.
When flameless venting is applied to dusts with relatively low melting points, such as resins, for instance, the powder can melt at deflagration temperatures, and on cooling, the solidified product blocks the mesh of the flameless device. In an extreme case, this would prevent effective venting. Examples of such dusts are plastics, resins and some types of coal. Very similar phenomena can also be observed with coarse and fibrous dusts, where their particles are different in size. The size of particles and their type (organic, metal, fibrous, coarse) plays a crucial role when choosing proper explosion protection. And it all comes down to the efficiency of a flameless venting device. Dust characteristic is not the only one you need to focus on. The volume of the protected vessel is another important parameter to consider, but not only volume itself but also the shape. This may present a challenge to many customers as they need to be able to evaluate if a recommended device is truly the best option for them.
The importance of KST
One way to see if a flameless venting device suits your production process is to know which Kst has your material. Kst value is one of the most used parameters in dust explosion protection. It has three main categories, which are called ST classes. We have ST1, ST2, ST3 classes, which help us categorise the effects of an explosion. Other parameters, such as MIE and MIT (minimum ignition energy and temperature) are often mentioned in regard to explosion protection. The lower the MIE, the higher the risk of explosion, as a minimal amount of energy input can trigger a dust cloud explosion. MIT, on the other hand, is the lowest temperature of a hot surface that will cause ignition of a dust cloud and propagate flame.
Explosions become more dangerous and violent with each ST class. Major explosion protection manufacturers have their devices categorised according to these three ST classes. If you are considering flameless venting for your facility, always check to which Kst is the offered product suitable and that it has valid certification according to the proper standard. Flameless venting devices are more complex devices requiring much more information for correct assessment and efficiency.
Tomáš Wyka is technical director of RSBP.