The use of vortex hoods in masonry work (dust collection)

Status:

completed 07/2007

Aims:

Problems regarding dust collection have remained unsolved for many years in the area of masonry work. These include inadequately effective collection, particularly of very fine, respirable dusts; excessively complex technical solutions for wet collection (booths with water wall and slurry disposal), and unsuitable design concepts and the resulting inadequate protective action.

Small and medium-sized enterprises (the working of artistic and natural stone) and trade businesses (e.g. masonry businesses) are generally those affected.

New collection systems which have already proved effective in other areas of application (vortex hoods) are to be adapted for this area of use, in the first instance in order to improve dust collection. Use of the water bed for dust removal can be replaced by dry dust extraction, which is substantially more effective and easier to maintain. In addition to adaptation to the most diverse areas of application, the emphasis here lies upon optimization with regard to the purchase costs. In addition, dry dust extraction substantially reduces the operating costs, whilst at the same time increasing the dust collection and the filtration performance (return of purified air).

Activities/Methods:

For planning and creation of an installation suitable for use in practice, overviews of processing methods were produced, concepts for solutions developed in consideration of cost aspects, proven collection techniques adapted to the defined problem, a model workplace developed and erected, and standard methods developed for testing of the effectiveness.

In consideration of the new German Ordinance on Hazardous Substances (GefstoffV), the institutions for statutory accident insurance and prevention (BGs) see an urgent need for action. (It may be possible for criteria to be developed for specific processes or substances.)

The study project was performed in three phases: adaptation of existing, proven systems to the problem (pilot stage), implementation at a model workplace, and assessment/modification and description of the concepts for measures and of implementation of the results (testing in practice, publications, consideration of the results in bodies of regulations, etc.).

In the pilot phase, a model was developed in line with real-case specifications, fabricated, and its serviceability tested at Imtech's fluid laboratory. This stage was followed by comparative assessment with systems currently available for practical use. The assessment was performed, under reproducible conditions, at the dust testing facilities of the test body for dust filters (pilot plant at the IGF, the institute for hazardous substance research, in Dortmund) of the "Minerals and earths" expert committee. Improvements were observed, which were enhanced substantially further following a number of modifications to the test model. In certain working positions, however, completely satisfactory results were not achieved at this stage. Nevertheless, the vortex hood which was developed can be recommended for use in practice, as it already enables substantially improved dust conditions to be attained at the workplace. The results were documented and presented to a broad public at the "Stonetec 2007" trade fair in Nuremberg.

Results:

For dust collection in manual masonry work, a dust collection and filtration system was developed which studies have shown to be substantially more effective. With only a few exceptions, the dust values measured both at the worker and in the immediate vicinity were shown to lie below the limit values of 10 mg/m³ for inhalable dust and 3 mg/m³ for respirable dust. The studies were conducted in each case with sandstone (with a quartz content of 15% to over 30%) and granite (with a quartz content of approximately 17%). With a small number of exceptions, the measured values for fine quartz dust were also substantially below the present limit value of 0.15 mg/m³.

Under certain exceptional circumstances (the worker beginning the grinding process perpendicular to the direction of extraction, etc.), higher concentrations of dust may be emitted from the collection area and briefly lead to higher exposure levels.

This problem is to be resolved by further technical development. If necessary, this exceptional case must be resolved by organizational measures (instruction procedures). To date, the vortex hood has not been tested in practice. Introduction of the hood in practice necessitates measures on a varying scale; these primarily entail persuading businesses to use new vortex hoods in the future rather than the familiar wet-type suction walls of the past.

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