Post on 27-Dec-2015
Slide 1Carlos Gomes – Bin Hu – James Freihaut
MindBend 2005
Resuspension of allergen-containing particles under mechanical and aerodynamic forces from human walking - Introduction to an experimental
controlled methodology
Bin HuCarlos Gomes
Advisor: James Freihaut
Indoor Environment CenterDepartment of Architectural Engineering
Pennsylvania State University
April 09, 2005
Slide 2Carlos Gomes – Bin Hu – James Freihaut
Asthma related statistics 18 million Americans (6% of US population) affected 5,000+ death per year in the US 13 billion USD per year Continues to increase
Research Motivation
http://aspe.hhs.gov/sp/asthma/overview.htm
Slide 3Carlos Gomes – Bin Hu – James Freihaut
Particles-allergen Resuspension
dp
5-10nm
Allergen
Carrier particle
0.1-50m
Allergen Type Animal/PlantCarrier size
rangeTime to settle in a
room
Der p 1Der f 1
House Dust Mite
10-25m 30 minutes
Bla g 1, g 2, Per a 1
Cockroaches >10m 30 minutes
Fel d 1 Cats50% >9m50% <9m
24 to 48 hours
Can f 1 Dogs Same as cat Same as cat
Amb a I, Bet v I Pollen 15-25m 30 minutes
Carrier particleParticle sizeSurface Properties• Chemical functional groups• Charge distribution• MorphologyEnvironmental Conditions• %RHReservoir Perturbation
Slide 4Carlos Gomes – Bin Hu – James Freihaut
Particle Resuspension
Reservoir-air aerosolization pathways
Mechanical• Shoe Friction• Floor Vibration
Aerodynamic• Velocity• Turbulence
Electrostatic• Human built up to 10,000 V
Adhesion + Gravitational• Van der Waals
Relationship among Force components and Resuspension - Not Understood
ElectrostaticFieldVibration
Air Currents
+
__ __ __ __
+
+
Friction
RF[m-1]=Cair/Cfloor
RR[min-1]=G/(A.Cfloor)
Slide 5Carlos Gomes – Bin Hu – James Freihaut
Aero-Electro-MechanicalRe-suspension
10-10 10-8 10-6 10-4 10-2
Aerodynamic DrivenRe-suspension
Resuspension Factor, “Constant,” (m-1)
Thatcher, et. al. (1995) 1- 25 µm
Buttner, et. al (2002)1.8 x 3.5 µm fungal spores
Karlsson, et.al.(1996)6.0 x 4.0 µm spores
Hambraeus, et. al. (1978)Residential
Nuclear storage studies (1960’s)
Resuspension-Review
Findings - Resuspension depends on:• Types of activities• Intensity activities• Reservoir dust load• Type of flooring• Particle size• Type of allergen• Relative Humidity ?
Sehmel, G.A., 1980, “Particle Resuspension: A Review,” Environment Int., 4, 107-127Nicholoson, K.W., 1988, “ A Review of Particle Resuspension,” Atmospheric Environment, 22, 12, 2639-2651
Limitations of previous studies: • Wide range of conditions and particles type• No control or characterization of ambient conditions,
floor surface type, dust types, reservoir dust load, activity intensity
• Particle size relationships among airborne and reservoir sources frequently not given
Consequences• Not possible to use literature data to make inhalation
dose-risk analysis in building simulations and achieve acceptable certainty in trends.
• Need controlled condition investigations with well characterized perturbations, reservoirs and time-resolved airborne measurements.
Slide 6Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Controlled: Temperature &
Relative HumidityParticle Free Air
Sampling
AllergenContent
CascadeImpactor
ELISAAnalysis
Resuspension Chamber
Physical and aerodynamic analysis of:• Known Particle Size• Known Particle Allergen Content• Known Surface Properties
Perturbance:• Vibration• Air Puffs• Electrostatic
Research Process
ParticleCounters
Slide 7Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
• Overall dimensions: 400x200x200 mm
• Test plate dimension: 100x100 mm
• Controlled Ambient Conditions
• Controlled particulate matter
• Incorporates mechanical and aerodynamic perturbances
Experimental Chamber
Slide 8Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Floor samples
• Representative of residential buildings
• Hardwood, carpet, linoleum
Controlled Surfaces Properties
Slide 9Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Calibrated dust• Quartz, aluminum oxide,
polymer, silica, etc
Allergen dust• Roach body parts• Cat hair• Dog hair• Dust mite
Controlled Dust Properties
Known properties
• Density
• Particle size distribution
• Allergen concentration
Slide 10Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Floor vibration
Vibration Signal
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0
Time (sec)
Am
plit
ud
e
Simple functions:
• Sinusoidal, square, triangular, etc.
Floor vibration due to human walking
• Measured in the field
Slide 11Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Air-puff
Air motion due to human walking• Published information inexistent
• Walking experiment with CO2 vapor
• Visible horizontal air velocity 1-1.5 m/s
1.5 m/s0.5 – 1.0 m/s
1.0-1.5 m/s
Slide 12Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Sampling Equipments
Optical Particle Counter
• 0.3 – 2+m, 8 bins
Cascade Impactor
• 0.4 – 9+m, 8 stages
• Particle shape
• Allergen concentration
• Determination of resuspended particle size distribution
• Particle size resolved allergen concentration
ELISAAnalysis
Slide 13Carlos Gomes – Bin Hu – James Freihaut
Resuspension Research
Methodology put together and tested
Experiments
• Test the methodology
• 26ºC, 45%RH
• Calibrated quartz and roach dust
• Carpet and linoleum
• Vibration, air-puff, vib.+air
• 12 experiments
Slide 14Carlos Gomes – Bin Hu – James Freihaut
Research – Experiments Results
Experimental observations:
• Resuspension in first two minutes
• Air had greater impact than vibration
• Higher resuspension rates on linoleum than carpet
• Roach dust is easier to resuspend than quartz
Carpet Linoleum
Quartz
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
Vibr Air Vibr+Air
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
Vibr Air Vibr+Air
Roach dust
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
Vibr Air Vibr+Air
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
Vibr Air Vibr+Air
Maximum:RR=3.22x10-3 min-1
RF=8.06x10-5 m-1
Slide 15Carlos Gomes – Bin Hu – James Freihaut
Conclusions and Recommendations
Conclusions:
• Valuable tool to create a database of RR&RF for particle resuspension, e.g. allergens, spores responsible for risk of disease development.
• First results are consistent with the literature review.
• Re-suspension parameters used in activity-based inhalation exposure risk models imbedded in building air flow simulations.
Recommendations:
• Improve floor disturbance characterization and expand floor disturbance to include an electrostatic field.
• Large chamber and field studies to validate the surface disturbance re-suspension data, models.
• Develop rapid field tests – swab swipe for hard, smooth surfaces and vacuum filtering for rought surfaces – to determine reservoir source strengths at site
10-2
Sehmel, G.A., 1980, “Particle Resuspension: a review”, Environment International, Vol.4, pp.107-127
10-10
Gomes and Freihaut 2004
10-6 10-3
Resuspension Factor Comparison
RF [m-1]