EXTRACTION INSTALLATIONS AND ATEX IN WOODWORKING
An explanation, especially for woodworkers
WHAT IS ATEX?
Atex is the everyday name of the European Directive 2014/34 / EU, which provides frameworks for dealing with explosion hazards. (Atex is a contraction of the French Atmosphères Explosibles.) It lays down, among other things, how the explosion risk can be divided into classes and categories and what the minimum risk reduction level should be in those cases. In other words, a formalization of the subject of explosion risk. In fact, the Atex Directive consists of two different Directives, Atex 153 and Atex 114.
Atex 153 is a workplace guideline. It describes how a (wood processing) company should deal with the dangers of dust explosions in the workplace and workplaces are divided into danger zones of increasing severity (so-called Atex zones). Atex 153 is included in the Working Conditions Act and therefore has consequences for all companies that work with combustible materials, including wood processing. In the context of the RI&E, they have to make an inventory of whether there is a risk of explosion somewhere in the company (click here for an explanation). If so, one will have to deal with the formalities of Atex 153, such as drawing up an Explosion Safety Document. Various branch organizations in the wood sector provide extensive and adequate information about this.
Atex 114 is a product guideline. This sets requirements for equipment that is intended to be used in explosive atmospheres, ie Atex zones. This concerns products which in themselves are an ignition source, usually electrical components. These must be approved by a body designated by the EU (Notified Body) and then receive an Atex certificate, which states in which danger zone the product can be used. If there are no Atex zones (according to Atex 153) in a company, then no Atex equipment (according to Atex 114) is required. In other words, equipment that is not in an Atex zone is not covered by the operation of Atex 114.
EXPLOSION SAFETY OF EXTRACTION EQUIPMENT
Since, as explained here, there are no Atex zones in the average timber company, Atex 114 is unusable in determining the explosion risk of extraction present there, whether it is inside or outside. Simply put: you cannot get an Atex certificate from an extractor. Then we have a problem with the risk assessment of extraction equipment, because it is quite clear that there is indeed a risk of explosion. However, this danger is not in the components used, but in the dust-filled interior of the device.
How should the explosion risk of wood extraction then be assessed? This question is particularly important with indoor extractors. Can a dust explosion occur in such an extraction unit and if so, how can safety in the workplace be guaranteed? Explosion protection experts tend to divide the interior of the device into Atex zones. That is allowed, but it makes little sense, because no ignition sources are built into those internal Atex zones. Naturally, this has been taken into account in the design. Atex 114 therefore offers no solution here either.
In practice, a dust explosion in the appliance will be the result of an internal fire, which in turn results from the suction of external sparks, for example from a sawed-through nail or a jammed sanding belt. (The energy of a spark in itself is not enough to ignite a wood dust cloud, flames are needed for that). It is not technically possible to prevent such a thing from happening and the extraction unit will therefore have to be constructed in such a way that the consequences of both a fire and an explosion are manageable. The Atex guidelines cannot help with how this should be done, but fortunately European standards are available to us.
For outdoor installation there is the standard NEN-EN 12779. Because there is no outdoor workplace, the explosion safety requirements are mainly limited to preventing an explosion from entering the device. This includes explosion check valves, U-turn diversions with explosion relief and facilities for extinguishing a fire. After all, fire almost always precedes an explosion.
The most important requirements at a glance:
- The device must be completely closed and operate at negative pressure (open extractors, such as one-bag extractors with filter element, may no longer be supplied)
- The dust-containing part of the interior must be limited in volume. This can only be achieved by keeping the filter surface as small as possible and - very important - using the outside of the filter elements as the dust side.
- Pressure shock resistant construction (200 millibar). Due to the limited dimensions of the extractor, no explosive flame front can form, at most a violent combustion with a pressure of up to 200 millibar. The construction of the extractor must be calculated and tested for this.
- An autonomous extinguishing system must be installed.
This is all the case with the new DM series from Riedex, however much of the equipment manufactured in the Netherlands traditionally does not meet this requirement. We are therefore proud to be able to state that Riedex is the first Dutch manufacturer to supply indoor extraction entirely in accordance with the new standard NEN-EN 16770.
Ried, July 2019,