What protection systems should be used for devices operating in explosion hazard zones?

Dusted and polluted air is a serious problem. If not properly controlled, it may lead to dangerous consequences for the people, causing respiratory diseases, and for the processing machines. Processing machines when operating in dusted and badly ventilated production halls may cause fire or even explosion. Therefore, in order to create a safe work place for the people and for the machines, every air filtrating device and machine has to be equipped with adequate protective systems.

Dusted air and explosion – what is the relation?

Some dusts are combustible, they burn fast and rapidly – such as dust produced in wood processing. At the same time, combustible dusts can hang in the air for a long time. When the dust concentration in the air happens to be between the upper and lower explosivity limit, then the explosion atmosphere occurs. In such conditions, any ignition soruce is enough for the dust cloud to catch fire and explode. The consequences of such hazard are usually tragic. It is however, possible to avoid explosion, if the dust concentration in the air is either below the lower or above the upper limit of explosivity – in the first case, there is too little dust to be ignited, in the second case, there is not enough oxygen for the dust to burn.

Protection systems for air filtration installations

In order to minimize the risk of explosion in a production plant, the key solution is to install an efficient dust collecting system. One needs to remember, however, that the filtration system itself is also at risk of explosion and fire, therefore, it has to be equipped with adequate protection devices which either prevent or minimize the consequences of explosion or fire. Here are some of them:

• exhaust hoses with grounding – hoses used in dust collectors for conveying dusted air – they are made of durable poluretane with copper coated steel spiral. The hoses are grounded in order to dissipate electrostatic charges that may be produced by the friction of the dust inside the hose. This way any sparking and ignition source are elminated.
• explosion isolation flap valves – installed on pipes conveying dirty air to the filtrating device. In case of explosion the flap gets closed by the shock wave and cuts off the flame and fire from spreading to other parts of the system.
• explosion vents – (also called decompression panels) their task is to relieve or vent the explosion into a safe area. When explosion occurs, the panels open directing the pressure and flame of the explosion into a safe area outdoors. The area into which the explosion is directed should be without access for people and at appropriate distance from other buildings and installations in order to prevent additional fire or explosion. In case when there is not enough space to map such area, it is possible to use flameless venting system, which can be also used interior or close to other buildlings.

What kind of protection should be employed?

The appropriate selection of protective systems should be based on a thorough analysis in which, among other factors, the characteristics of the production plant and dust type are considered. The next step is to determine the risk in accordance to the ATEX directive, which defines three explosion risk zones:

All protective measures should be selected in order to minimize the risk of explosion. Solutions offered by Filtrowent are produced in compliance with the ATEX directive.