Airborne Particles in Welding

AIRBORNE PARTICLE SAMPLING AT A WELDING FACILITY IN THE USA

Airborne particles in the size range from 2nm to 30μm were sampled using the Aero Select at a flow rate of 20 l/min at a welding facility in the USA. Particles fractionated into sizes according to 12 separate size “bins”. By analysing the amount of substance of interest in each of the size bins it was possible to derive the mass size distribution over the entire aerosol particle size range. Chemical analysis of the samples was carried out using ICP to identify the size distributions of various materials.

Figure 3.1 shows an aerosol mass size distribution, fa(D), of Zn sampled at a welding facility in 2008. The distribution has a broad mode in the micron size range and a large maximum centred at 10 nm. The majority of the Zn mass (82%) is found to be in the nano range. The nano range mode is centred at about 10 nm. A wider mode or possibly two modes are located at the sub-micron and micron ranges. The total mass concentration of Zn in the air is 2,020ng/m3, which is much lower than the mass concentration of atmospheric background aerosol particles.

Figure 3.2 shows an aerosol mass size distribution fa(D) of Al sampled in the same welding site. The distribution has a broad mode in the micron size range and a small maximum centred at ~3 nm. This is a typical multi-modal distribution similar to the results observed earlier for lead in the work place (Gorbunov et al., 2009). The total amount of Al in the nano-range (D<100nm) is about 3%. The total mass concentration of Al in the air is 1,390ng/m3, much lower than the mass concentration of background aerosol particles (20,000-100,000ng/m3).

These are typical size distributions obtained over the full-size range. The distributions exhibit three main features: 1. the majority of the distributions are bi-modal and have a distinct mode in the nano-range, 2. the mass fraction of nanoparticles (1nm < 100nm).

equivalent-mass-concentrations-of-materials-in-the-air-and-deposited-in-the-respiratory-tract

Table I: Equivalent mass concentrations of materials in the air and deposited in the respiratory tract according to various metrics and the TSP for the background aerosol.

 

zn-aerosol-particle-mass-size-distributions

Figure 3.1: Zn aerosol particle mass size distributions dm/dLogD in ng/m3 measured at a welding facility in the USA. White bars represent aerosol in the air, grey bars represent size distribution corresponding to particles deposited in the entire respiratory system, and dark bars represent the size distribution corresponding to particles deposited in the alveolar and trachea bronchial range.

 

al-aerosol-particle-mass-size-distributions

Figure 3.2: Al aerosol particle mass size distributions dm/dLogD in ng/m3 obtained at the welding facility. White bars represent aerosol in the air, grey bars represent size distribution corresponding to particles deposited in the entire respiratory system, and dark bars represent the size distribution corresponding to particles deposited in the alveolar and trachea bronchial range.

 

REFERENCES:

B. Gorbunov, N. D. Priest, R. B. Muir, P. R. Jackson and H. Gnewuch (2009) A Novel Size-Selective Airborne Particle Size Fractionating Instrument for Health Risk Evaluation. Ann Occup Hyg, Vol. 53, No. 3, pp. 225–237.

Frank E. Pfefferkorn, Dhimiter Bello, Gilbert Haddad, Ji-Young Park, Maria Powell, Jon Mccarthy, Kristin Lee Bunker, Axel Fehrenbacher, Yongho Jeon, M. Abbas Virji, George Gruetzmacher, and Mark D. Hoover. Characterization of Exposures to Airborne Nanoscale Particles During Friction Stir Welding of Aluminum. Ann Occup Hyg, (Jul 2010) Vol 54, No. 5, pp. 486–503.

Acknowledgement: Dr D. Belo for supplying the size distributions.