Precautionary measures and regulations
Explosive substances must also be disposed of safely. This presupposes, first, a precise knowledge of the properties of fine-particle dust such as powder, flour, wood or metal dust. The more that is known about its combustibility and explosive behaviour, the more meaningful and purposeful the protective measures that can be taken. They include vacuuming up combustible dusts (except for dust with an extremely low minimum ignition power of ME < 1mJ). Only vacuums that comply with what is known as the ATEX Directive (94/9 EC of 2003) may be used for this. This Directive sets out inter alia the requirements for the characteristics of appliances for use in areas where there is a risk of explosion. It distinguishes between gas-ex and dust-ex areas, and categorises the equipment to be used for each.
Even machines with dust-ex protection cannot be used everywhere because areas where there is a risk of explosion place different demands on vacuums, depending on the extent of the potential risk. So the ATEX Directive defines different groups of appliances and categories of risk.
Group l machines are for use in underground mines (M1 and M2: M = Mining), while Group 2 machines are approved for use in non-mining areas. Both groups are subdivided into three risk categories, “very high,” (1), “high,” (2) and “normal.” (3). The ATEX requirements for vacuums are defined in line with these groups and risk categories.
Risk categories 1 and 2 (dust-ex areas of Zones 20 and 21) are usually permanently installed vacuum devices.
Mobile vacuums come into risk category 3. They may be used in dust-ex areas in Zone 22, where a dusty atmosphere capable of exploding occurs only rarely and for a short time (inter alia mills, warehouses, the pharmaceuticals industry, the chemical industry, the food industry, the electrical industry and the paper and powder processing industry). Since explosive dust in Zone 22 areas may also develop a toxic effect, the requirements for the filter efficiency of vacuums are the same as for dust classes M and H.
Machines approved for Zone 22 are identifiable by their B1 labelling according to DIN EN 60335-2-69 Annex AA. These machines have at least classification B1M or B1H and have been designed and built in accordance with protection class IP 54 (DIN 40050). In order to neutralise dangerous and explosive dusts, in some of these vacuums the hazardous substance vacuumed up is drawn through a water bath, whereas water-reactive substances must be vacuumed up and filtered dry. Some vacuums can now do both.
Challenge and solution
Choosing an appropriate vacuum is not an easy task. Essentially, the choice always depends on the risk assessment. The vacuum manufacturer should give good advice as a matter of course, drawing attention to technical details of the machine. Nowadays, a good vacuum has an effective filter cleaning system that shakes the filter out automatically, filter bags that are easy to use and can be disposed without allowing dust to escape, and locks that prevent erroneous operation of the vacuum. Users who pay attention to the operating instructions will always achieve the best possible cleaning result.Dr Marcel Schoch Freelance Journalist