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Vacuum systems and portable vacuums for potentially explosive areas
Several routes, one objective

In areas that carry a risk of dust explosion, vacuum systems and portable vacuums have an important job to do. At the same time, they require special measures to protect them against the explosion hazard. There are various technical options available for achieving this.

The author: Gerald Scheffels Freelance technical journalist

Clean and safe: this maxim applies to all production and storage areas subject to a risk of dust explosion. This is because dust deposits can be stirred up by a draught, for example, forming an explosive mixture with atmospheric oxygen if they are sufficiently concentrated. This risk can occur anywhere where organic materials are processed, manufactured, packed or stored in such a way that dust is produced.
The link between cleanliness and safety has meanwhile also been enshrined in standards and directives. Atex Directive 137 (1992/92/ EC), also known as the Workplace Directive, explicitly requires operators to keep the production environment clean and makes the classification of areas into zones dependent on the level of cleanliness. This means that if dust deposits are avoided in potentially explosive atmospheres, the hazard class is lower and the measures to be taken, for instance regarding explosion protection, are less onerous. This cuts costs – and reduces the risk of explosion.
The Ordinance on Industrial Health and Safety (BetrSichV), which enforces the requirements of Atex Directive 137 in Germany, adopts exactly the same approach. It holds operators accountable and requires them to produce an explosion protection document setting out the possible risks and the measures implemented to minimise those risks. This requirement is by no means disproportionate when it comes to dust explosion protection. Experts estimate that there are over ten times more dust explosions than gas explosions. Against this background, it is clearly essential in many production sectors in the interests of safety to give some thought to cleanliness – or more accurately to the avoidance of dust deposits. There are three main options here.
The first is to use closed installations which do not allow dust to escape. As this is not always entirely possible, however, the second option is to extract the dust directly at the point of source (use of dust extractors in accordance with EN 60335-2-69). Since this option is likewise not usually one hundred per cent successful, the third option is regular and thorough vacuuming of dust deposits – not only from the floor but also from machinery, piping and walls. EN 60335-2-69 refers to the “use of industrial vacuums” in this connection. The applicable standard thus provides for both meth-ods of removing hazardous dusts.
Making explosive dusts harmless
Modular systems which can be adapted precisely to the specific operating conditions, and which in all cases comply with the applicable dust explosion protection regulations, are available for direct point-of-source extraction and for vacuuming alike.
These systems harness some ingenious technologies for making explosive dusts harmless. One example is the upstream wet separator from Ruwac. The way it works is quite simple: the vacuumed material is channelled through a liquid and extinguished if it is an ignition source. Alternatively, a compact spark trap, which renders the sparks harmless by purely mechanical means, can be used in many applications. This is the recommended option for grinding aluminium and magnesium, for instance (the dusts from which are likewise combustible).
Hazardous dust vacuum systems from Ruwac are designed on a modular basis to allow individual configuration. Users requiring portable industrial vacuums for areas carrying a risk of dust explosion can choose from standard models which – again because of their modular design – can similarly be adapted to specific conditions. This range also includes the DS 1220 FS series, which was developed specifically for extracting fine and very fine dusts and is also available in an explosion-proof version.
Portable vacuums or static system
In each case the user also has to make a basic decision whether to use portable vacuums or a static vacuum system designed for use in a potentially explosive atmosphere. With static systems a network of pipes is installed in the facility, with connection points to which vacuum accessories can be connected. As soon as an accessory is attached, the central vacuum unit switches on automatically. This type of system is particularly cost-effective in larger and multi-level facilities (e.g. mills) as well as in applications requiring very frequent or even continuous vacuuming. Ruwac’s modular system allows users to choose between these two options.
The industry thus offers several different ways of implementing the “clean and safe” maxim and hence of minimising the risk of dust explosions. Case studies show that even in complex applications such as waste disposal facilities, effective dust explosion protection can be achieved with relatively simple, purely me-chanical means. However, experience in the design and construction of this type of safety-related equipment is essential, and the function and operating status of the equipment should be continuously monitored by means of a control system.
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