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]