Determination of the capture efficiency of welding fume extraction devices

Status:

completed 10/2002

Aims:

The capture efficiency is the decisive criterion for welding fume extraction devices. It is currently measured by a number of widely differing methods. Experimental studies were to be conducted in order to determine whether a uniform assessment of capture elements is possibly when different test methods are employed. A suitable test method was to be established and a minimum value for the capture efficiency had to be defined in accordance with the state of the art.

Activities/Methods:

A representative cross-section of capture elements was selected in conjunction with the Metal and Surface Treatment expert committee of the institutions for statutory accident insurance and prevention, and with manufacturers of welding fume separators. Each capture element was subjected to four different test methods. The tests involving methods employing emission sources (tracers, fumes) were performed on test benches at the BG Institute for Occupational Safety and Health (BIA). The test benches consist of a cabin with a downstream funnel, dust measurement tunnel, and extraction equipment. The capture elements were positioned in the cabin as specified in the draft standard, and connected to a separate extraction system. The component of tracer gas or actual welding fumes which is not captured was measured in the measurement tunnel. The tests involving the other two test methods (air speed, air speed profile) were performed in the same cabin, but in this case without extraction. Disturbances resulting from interferent cross flows were thus excluded.

Results:

For welding fume extraction devices a minimum air velocity of 0.4 m/s is required at a defined point in front of the hood. In order to attain a capture efficiency of 60% for welding fumes, a certain volumetric airflow at the hood must be defined. Measurements were performed in a standardized test cabin for this purpose. A tracer gas may be employed as an alternative to welding fumes. For welding fume sources with fume extraction immediately behind the welding point, capture efficiencies of between 42% and 90% were achieved, depending upon the torch orientation. For welding fume classes W3 and W2, new filtration levels of 98% and 99% were defined, including statistical validation. For class W1 units, the extraction efficiency remains at 95%, as previously stated in the German test principles for welding fume extraction devices. This value includes the statistical validation, however. The results were adopted as new requirements in prEN ISO 15012 "Health and safety in welding and allied processes - requirements, testing and marking of equipment for air filtration", Parts 1 and 2.

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