Two-Zone Model Application to Breathing Zone and Area Welding Fume Concentration Data

Abstract

This study assessed a professional pipefitter/welder performing shielded metal arc welding on carbon steel under field conditions. The resulting breathing zone (near field) and area (far field) welding fume concentration data were applied to the two-zone model for the purpose of determining field-derived personal exposure emission (generation) rates during actual welding work. The study is unique in that one welder was evaluated under high production conditions for 2 days at two different welding locations: a boiler room and a breezeway. Samples were collected and analyzed for total particulate following NIOSH Method 0500 and for select metals following NIOSH Method 7300. Breezeway average personal breathing zone sample total particulate concentrations ranged from 2.89 mg/m³ to 4.38 mg/m⁽³⁾, Fe concentrations ranged from 0.53 to 0.63 mg/m³, and Mn concentrations ranged from 0.10 to 0.12 mg/m³. The boiler room average personal breathing zone sample total particulate concentrations ranged from 4.73 mg/m³ to 5.90 mg/m³, Fe concentrations ranged from 0.48 to 0.85 mg/m³, and Mn concentrations ranged from 0.06 to 0.16 mg/m³. Average arc times ranged from 20 to 25% of the total sampling time. Both tracer gas and anemometer techniques were used to estimate ventilation of the boiler room. The steady-state form of the two-zone model was applied to long-term and short-term sample total particulate, Fe, and Mn concentrations obtained during welding in the boiler room and breezeway. The average generation rate in the boiler room was 39.2 mg/min for TP, 6.4 mg/min for Fe, and 1.3 mg/min for Mn. The average generation rate in the breezeway was 40.0 mg/min for TP, 6.6 mg/min for Fe, and 1.2 mg/min for Mn. The field-based generation rates were considerably lower than laboratory-derived published emission rates of between 280 and 650 mg/min for TP. This study emphasizes the need for field-derived welding fume generation rates and showed the personal breathing zone and area sample concentrations can be described by the two-zone model in a way that may help the industrial hygienist estimate exposures.

[Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resource: Tables detailing the personal breathing zone and average area sample results for breezeway welding and boiler room welding, two-zone modeling results, and boiler room welding personal breathing zone and area sample results with mixing fans on.]

Keywords:

• exposure assessment
• generation rate
• model
• tracer gas
• welding

ACKNOWLEDGMENTS

The authors wish to thank the team of professionals that assisted with the field activities for this exposure assessment. This study was funded by companies involved in the welding industry, including the following manufacturers of welding consumables: Lincoln, Hobart, ESAB, Eutectic, and Sandvik. The pipefitter was performing a routine and scheduled field project and was paid by his employer. One of the authors (FB) has designed and evaluated the effectiveness of numerous ventilation systems and testified as an expert in cases involving welding exposures.

Notes

^A Average values are presented here. Those values below the method detection limit were not included in the analysis.

^A Data presented are unweighted averages of all short- and long-term area samples.

^B Data presented are unweighted averages of all short- and long-term area samples.

^A Mixing fans created destratification of the welding plume, resulting in higher sample results than when fans were off.