Wednesday, November 09, 2005

Ultrafine [dare we say nano] particles in an industrial setting

Occupational Hazards isn't a peer reviewed journal, but it here reports some cutting edge research on particle exposure in the occuaptional environment, which in turn provides information for exposures at home.

Direct-fired gas heaters prove to be a major source of ultra fine particles.

The major finding was, regardless of mass "Number concentrations of ultrafine particles inside the facility ranged from 15 to 150 times greater than outside the facility and were highly dependent on season. "Even in the assembly area where number concentrations were lowest, ultrafine particles were on average 15 times greater inside the facility than outside, regardless of the season."

Maybe 50 years ago, particle counting, collected via impinger, was the way to assess particle exposure. Sizing was visual. Then, balances got better, and mass collected on a filter became the measure. Cyclones or impacters provided sizing. Personal, breathing zone samples became feasible.

Now there are instruments which give real time, size specific particle counts, although personal samples are not yet feasible.

Particle number is plausibly the best measure for contact effects in the respiratory system - the number of spots impacted or phagocytic cells affected.

So now we identify a new and major source of particles, direct fired gas heaters. It's time to bioassay these particles in the rat, along with the effluent from a natural gas powered internal combustion engine.

Study: Gas-Burning Heaters Cause Ultrafine Particle Spike in Engine Plant - 10/10/2005

Research has shown that "hot" processes such as welding and high-speed machining can generate ultrafine particles (particles with a diameter less than 100 nanometers) that may be harmful to workers' health. But a new study of nanoparticle levels in an Indianapolis engine machining and assembly plant concludes that a major source of nanoparticle emissions was the exhaust from its gas-burning heating system.

Researchers involved in the study found the greatest ultrafine particle number concentrations in the block-head-rod area, and they believe that the majority of ultrafine particles generated in that area came from direct-fire, natural gas burners that heated the supply air.

Researchers observed a nearly 1,000-percent spike in number concentration of ultrafine particles in the supply air when the heating system was operating compared to when it was turned off…


Ultrafine Particles 'Prevalent' Throughout Facility

  1. Repeat analysis showed that these ultrafine particles "persist in the workplace over long time periods."

Mass Concentration Not a Good Indicator of Number Concentration

Overall, the study concludes that mass concentration was not a good indicator of number concentration.
"Mass concentration was low (less than 0.2 mg per cubic meter) where direct-fire heaters produced the greatest number concentration (more than 1 million particles per cubic centimeter)," Peters says. "Consequently, to the extent that health effects are related to ultrafine number exposures, current mass-based regulations may not be sufficient to protect workers in these areas."

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