Emissions of hazardous substances from machines

Status:

completed 12/2002

Aims:

The problem was to identify the best approach to measure and assess emissions of hazardous substances (dusts, gases, fog etc.) from machines. The investigation was based on the standards series EN 1093 "Safety of machinery - Evaluation of the emission of airborne hazardous substances" and especially on Part 2 "Tracer method" and Part 3 "Bench test method". The project had a planned running time of several years and brought together eight research institutes from six European countries. The aim of the total project was to define test standards for specific machine groups, so called C standards, so that machines can be tested under reproducible conditions and all test organisations will get the same results for the same machines.

Activities/Methods:

A first step was aimed to determine the central test parameters, using reference sources of dusts and gases. Among these parameters counted the position of the emission source in the test chamber, the air velocity, the form and length of the measuring tunnel, adequate measurement points and instruments etc. These parameters set the framework for standardised test conditions under which a number of simple machines emitting dusts and gases were investigated on test benches in different European countries. The aim consisted in defining test standards for specific groups of machinery so that tests on these machines are everywhere conducted under reproducible conditions and always yield the same results. Manufacturers of machines are thus given the opportunity to demonstrate compliance with the basic requirements of the Machinery Directive in terms of pollutant emissions.

Results:

A large number of permutations were studied with regard to air speed, dust source positioning, and number of measurement filters, in order to optimize emission measurements on the different test benches of European OSH institutions. The following four settings were favored for measurement of dust emissions: emission measurement with the greatest possible number of measurement filters distributed evenly over the channel cross-section; positioning of the dust source in the direction of the chamber funnel and at a distance of 2 metres from it; positioning of the dust source at mid-height of the chamber or above, and an air speed within the measurement chamber of 0.5 m/s or higher. Each method has its advantages and disadvantages: The emission measurement with the greatest possible number of measurement filters requires a compromise between the number of measurement filters (a more accurate measurement of the dust distribution profile) and the justifiable cost. In accordance with VDI 2066 Part 1, "Measurement of particulate matter in flowing gases, gravimetric determination of dust load - overview", the cross-sectional area of a rectangular measurement channel must be divided into sub-rectangles of equal size, upon the diagonal intersections of which the measurement filters are to be placed. Either four or nine sub-rectangles and filterpositions could therefore be employed. In most cases five filters were used and the fifth filter was placed at the center of the channel cross-section. If the mean value is calculated from the results yielded by these five measurement filters, the above measurement standard is violated. The effect of the resulting deviation at the dust profiles measured was however so low that this method of determining the mean is acceptable. The increase in the distance between the dust source and the chamber funnel results in more even dust distribution where particles are small, owing to the longer dwell time and where particles are larger it results in higher sedimentation losses. The system was optimized for low sedimentation losses. The sedimentation losses can be reduced further when the blast from the dust source is directed towards the measurement channel and the vortexing in the measurement channel is intensified by the generation of further air turbulences at the start of the measurement channel. The system was also optimized for low sedimentation losses through different positions in height of the dust sources. The dust sources studied were positioned at three heights (at one-quarter, half and three-quarters of the chamber height). Whereas a higher sedimentation loss occurred at the lowest height, particularly where larger particles were concerned, the other two heights yielded results delivered virtually the same result when averaged over all measurement filters. The increase in air speed seems problematic because a favorable dust transport is ensured from the dust source to the measurement filter, it also deconcentrates the free dust strongly. In addition, the air speed of 0.5 m/s does not correspond to industrial practice. The effect of the machine exhaust is also reduced, as the dust is transported away too quickly from the intake on the machine. This setting should not therefore be employed in future standardization activity.

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