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Transport efficiency and deposition velocity of fluidized spores in ventilation ducts

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Abstract

Experiments with dry, fluidized spores were conducted in a test apparatus to delineate the extent of spore contamination and deposition behavior under normal airflow conditions within a ventilation system. The surrogate biological warfare agent used in experiments was the spore-forming bacterium Bacillus atrophaeus. Viable-spore-counting methods were used in the study because they provide the most important number for estimating human health effects. Three common ventilation duct materials were evaluated: flexible plastic, galvanized steel, and internally insulated fiberglass. Transport efficiency ranged from 9 to 13% in steel and fiberglass ducts; transport efficiency was far less (0.1–4%) in plastic duct. Results showed that the deposition of surrogate biological warfare agent was significantly different in the three duct materials evaluated. All experimentally determined, dimensionless deposition velocities were in the range of theoretical predictions for dimensionless roughness, k +=10. All were 10–100 times greater than the velocities predicted for ducts with smoother surfaces, k +=0.1. For plastic duct, greater dimensionless deposition velocities were likely the result of charge forces between spores and surface. However, for the steel duct, a relatively large dimensionless deposition velocity was unexpected. These findings imply that building contamination will likely vary, depending on the specific type of duct material used throughout an affected area. Results of this study may aid in refining existing particle-transport models and remediation activities.

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Abbreviations

ANOVA:

Analysis of variance

APS:

Aerodynamic particle sizer

B. anthracis :

Bacillus anthracis

BG:

Bacillus globigii (B. atrophaeus)

BWA:

Biological warfare agent

C:

Coulomb

CFU:

Colony forming unit

C s :

Cunningham slip factor

D :

Duct diameter

d :

Particle diameter

HEPA:

High-efficiency particulate air (filtration system)

HVAC:

Heating, ventilating, and air conditioning (system)

k + :

Dimensionless roughness

L :

Duct length

PB:

Phosphate buffer

PBS:

Phosphate-buffered saline

R e :

Reynolds number

RH:

Relative humidity

SD:

Standard deviation

TSA:

Trypticase soy agar

V d :

Particle deposition velocity

U a :

Velocity in the duct

η:

Kinematic viscosity

u * :

Friction velocity

ρ:

Particle density

τ:

Particle relaxation time

ν:

Viscosity

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Acknowledgements

The authors wish to thank Don Schwartz, Joe Shinn, John Van Fossen, Souheil Ezzedine, and Kent Wilson. Work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.

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Authors and Affiliations

  1. Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA, 94550, USA

    Paula Krauter & Arthur Biermann

  2. West Desert Test Center, U.S. Army Dugway Proving Ground, Dugway, UT, 84022, USA

    Lloyd D. Larsen

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  1. Paula Krauter
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  2. Arthur Biermann
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  3. Lloyd D. Larsen
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Correspondence to Paula Krauter.

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Krauter, P., Biermann, A. & Larsen, L.D. Transport efficiency and deposition velocity of fluidized spores in ventilation ducts. Aerobiologia 21, 155–172 (2005). https://doi.org/10.1007/s10453-005-9001-z

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