TWI Technology Briefing 596 - March 1997
G J Carter and K Y K Chung*
FULL REPORT
Welding fume is the subject of legislation limiting the concentration to which workers may be exposed by inhalation. Compliance with the regulations is presently verified by measuring personal exposure using national procedures.
Background
To ensure uniformity of exposure measurement within Europe, a European Standard has been drafted for sampling airborne particles and gases emitted during welding and allied processes. It defines a test method for gravimetric determination of exposure to welding fume, and provides examples of samplers that may be used and how they might be positioned and secured in a worker's breathing zone. Advice is given on sampling in the presence of other airborne particles (
eg grinding dust) and on determination of exposure to individual fume constituents. The standard provides options in terms of the samplers and procedures used, but there are insufficient data to evaluate effects of these options on exposure measurement.
This work was to evaluate the effect of these sampling and procedural options during welding and grinding stainless steel, with attention to flux-cored arc and metal active gas welding processes. It is expected that information obtained here will be considered by the appropriate European standardisation committee when the draft standard is reviewed.
Objective
- To quantify the effects of sampling and procedural options described in a draft European Standard on measurements of welding fume exposure.
Experimental approach
The following aspects of the draft standard evaluated were the effect of:
- using different samplers
- positioning the samplers on either the right or left side of the face
- sampling welding fume in environments containing grinding dust
- using datasheet fume compositions rather than an analysis of the fume sample collected to calculate exposure to fume constituents and hence determine fume control requirements.
The evaluation procedure consisted of comparing fume exposures measured in the breathing zone of a breathing mannequin reference sampler with fume concentrations measured simultaneously as a result of inhalation through the mannequin's mouth. Inhalable dust samplers originating from UK, France, Denmark and Germany were tested (according to the appropriate national protocol), and a new sampler developed by the Health and Safety Executive to separate inhalable and respirable particles.
Generally, two of the same sampler type were evaluated together, so that the effect of mounting position (left or right of the mannequin's head) on exposure level could also be investigated.
Sampling was performed during welding of ASTM A312 304 stainless steel using 308 type wires for metal active gas (MAG) and gas-shielded flux-cored arc welding (FCAW) processes. Welding was carried out using a specially built test rig which maintained a fixed relationship between the torch and the mannequin.
The samplers were also tested for manual grinding of stainless steel to determine what effect the dust generated would have on gravimetric determinations of exposure to welding fume.
Fume from the samplers, the mannequin and a bulk fume sample generated in a fume box were analysed. Results were compared to manufacturers' datasheets.
Results and discussion
The samplers collected approximately the same amount of fume. For MAG welding, they oversampled by about 30% compared to the mannequin and by about 10% with FCAW. However, because the number of results was small and standard deviations were of the order of 10-20%, it is unlikely that significant differences in measurement of fume exposure levels will arise from using the specific samplers tested here. Approximately 70% of the fume was measured as 'respirable' using the HSE sampler. The effect of sampling position on measured exposure levels was variable. In five of eight tests performed the sampler nearest the weld (right side) provided the highest results, but the left side sampler provided the highest result on three other occasions.
The samplers collected grinding dust at approximately the same rate as the mannequin. Amounts of dust collected were significant, so that gravimetric measurement of welding fume exposures using samplers collecting inhalable particles will give rise to large errors.
Significant errors remained when using the HSE sampler, because 30% of the dust was measured as 'respirable'.
Large differences in composition existed between a bulk fume sample collected in a fume box, samples from the samplers and mannequin, and the datasheet analyses.
In many cases, the differences were not important because they occurred in elements which were not significant. Using the datasheet analysis in the MAG welding trials would have led to under-estimation of the risks and fume control requirements.
Main conclusions
- The samplers collected approximately the same amount of fume, and sampling efficiency was approximately the same for MAG and FCAW.
- Effect on exposure measurement of placing the samplers in different positions (left and right side of the head) was variable. Consequently, sampling position cannot be defined meaningfully in the sampling protocol.
- All samplers collected grinding dust. Therefore, gravimetric determination of welding fume exposure in atmospheres containing dust will be incorrect and high.
- Large differences existed between datasheet fume composition, analyses of bulk fume samples and analysis of fume from the samplers and the mannequin.
- The 'respirable' sample, collected using the HSE sampler in environments containing only welding fume, was 70% of total fume collected. In grinding dust environments this was 30% of total grinding dust.
Recommendations
The UK, French, Danish, German and HSE samplers are recommended for measuring exposures to welding fume in atmospheres not containing grinding dust particles. If other inhalable particles are present concurrently, then the results obtained will be incorrect and high.
When grinding dust is present, the HSE sampler is recommended. The measured 'fume' concentrations will still be high because 30% of the grinding dust will appear with the fume in the 'respirable' fraction. However, the error will be less than obtained using the other inhalable samples.
It should be noted that caution is necessary when using manufacturer's datasheet fume analyses to assess necessary fume control measures.
*Health and Safety Laboratory
Member Report No. 596-1997
Examination of the sampling protocol defined by draft European/International Standard prEN ISO 10882-1 when sampling airborne particles from stainless steel welding
