1. No category

RESUSPENSION OF ALLERGEN-CONTAINING PARTICLES UNDER
MECHANICAL AND AERODYNAMIC DISTURBANCES FROM
HUMAN WALKING - INTRODUCTION TO AN EXPERIMENTAL
CONTROLLED METHODOLOGY
C. Gomes1,*, J. Freihaut1,*, W. Bahnfleth1
1
Indoor Environment Center, Architectural Engineering Department, Pennsylvania State
University
University Park, PA 16802, USA
ABSTRACT
Epidemiological evidence indicates that common environmental allergens found in building
reservoirs are strongly associated with the development of bronchial hyper-reactivity (BHR)
or asthma, affecting up to half the population in North America and Europe. Although they
are rarely life threatening, these diseases cause much distress and lost time from school and
work. These diseases are believed inhalation sensitized and developed, suggesting an
aerobiological pathway of allergen-containing carrier particles from reservoir to occupant
respiration. This study presents and develops a controlled and characterized method to explore
the influence of human walking on the aerosolization of allergen-containing particles. Time
resolved particle size distribution and allergen content are measured for particles resuspended
from representative samples of flooring materials and for different sets of floor disturbances
in an environmentally controlled experimental chamber. Initial results, when placed in the
context of previous investigations, indicate the method can be utilized to develop a database
for particle resuspension rates.
INDEX TERMS
Particle resuspension, Resuspension rates & factors, Allergens, Bio-aerosols, Asthma
INTRODUCTION
Epidemiological studies indicate continuing significant increases in health care and
hospitalization of patients for respiratory system related diseases such as asthma. According
to the Center for Disease Control and Prevention (Anon), approximately 6% of all Americans
suffer from asthma and approximately 5,000 people die each year of asthma or related
complications. The economic burden of this illness in the United States is estimated at $12.7
billion dollars per year (Anon A). Symptoms of asthma may be triggered in genetically
predisposed individuals and developed in non-atopic individuals by exposure to allergens.
Common indoor allergens are found in cat and dog fur or saliva, cockroach and dust mite
droplets and body parts. After disintegrating, these materials adhere to inert dust in carpets,
upholstery, and other reservoir surfaces making allergens available for secondary
aerosolization when disturbed by human activity (walking, vacuum cleaning, etc.). Specific
allergens associate with different ranges of carrier particle sizes (NAS 2000) and, after reentrainment, can stay airborne for relatively long periods of time as respirable particles.
•
Corresponding author email: [email protected], [email protected]
The first studies examining the impact of human activity on particle resuspension were
conducted in the 1960’s with radioactive material from the floor of nuclear facilities. The
resuspension factors from these studies and from more recent ones were summarized by the
US Nuclear Regulatory Commission (NRC 2002) and ranges from 6x10-8 to 7x10-4 m-1.
Sehmel (1980) presented a summary of particle resuspension factors caused by mechanical
disturbance from indoor human activities (walking and sweeping) and outdoor activities
(pedestrian walking and vehicular traffic), ranging from 1x10-10 to 3x10-2 m-1. Until the
1990’s, occupancy-related particle resuspension in residential and offices buildings was
seldom explored. Extrapolated resuspension values from the previously nuclear material
studies had very limited application. More recently, due to the increase of particulate-related
respiratory diseases (in particular asthma) and the emergence of CBW attacks on civilian
populations, several studies on indoor particle resuspension have been performed (Table 1,
Weis et al. 2002, Matsumoto 2003). Table 1 summarizes relevant findings.
Table 1. Summary of Particle Resuspension Studies
Source
Hambraeus
et al.
1978
Thatcher
et al.
1995
Location
Hospital
Operation
Room
V=112 m3, A=35 m2
Residential Bldg
1st floor
V=360 m3
A=150 m2
Floor
Type
Vinyl
Carpet
Wood
Vinyl
Karlsson
et al.
1996
Experimental
Room
A=20 m2
NR
Karlsson
et al.
1999
Experimental
Room
V=45 m3
A=15 m2
PVC
Buttner
et al.
2002
Experimental
Room
Resemb. residentl
4.0x4.0x2.2 m
Single family
home
Vinyl
Com. carpet
Resid carpet
Ferro
el al.
2004
Wood
Rug
Ambient
Conditions
T=NR
RH=NR
Ventl=off
No air leakge
T=NR
RH=NR
Dust
Bacteria-carrying
particles
dp=3-6 µm
ρ=NR
Inert dust
ρ=1 g/cm3 (assm)
Floor Load
1.5x103
1.6x103
3.4x104
cfu/m2
Average
39 µg/cm2
Grass Pollen
6x4 µm
dm=6.3 µm
ρ=1 g/cm3 (assm)
Freeze dried spores
Bacillus Subtilus
1.8x0.9 µm
davg,aglom=12 µm
ρ=1.3 g/cm3
Penicillium
Chrysogenum
Spores
1.8x3.5 µm
NR
2.6x107 #/m2
T=NR
RH=NR
1 person walking
at 0.7 m2 table
1 hour
1x108 #/m2
or
120 mg/m2
T=NR
RH=NR
1 person walking
4 persons walking
75 steps/min
1x106 cfu/m2
1x107 cfu/m2
HVAC, HEPA
5 Pa pressz
T=NR
RH=NR
T≈20°C
RH=NR
Walking in
prescribed pattern
1 minute
NR
Activity
4 persons walking,
30 min
Mopping, 10 min
Hair dry jet, 10 min
4 persons
walking and
Sitting
Walking on wood
Vacuum on wood
Dance on wood
Resuspension
Resusp.
Part. Size
2.5x10-3 m-1
2.0x10-4 m-1
1.2x10-3 m-1
1.65x10-8 min-1
7.33x10-9 min-1
3.00x10-7 min-1
1.38x10-6 min-1
6.33x10-6 min-1
5.67x10-7 min-1
8.0x10-2 m-1
7.8x10-2 min-1
3-6 µm
3-6 µm
3-6 µm
0-0.5 µm
0.5-1.0 µm
1-5 µm
5-10 µm
10-25 µm
>25 µm
6.3 µm
6.3 µm
1.8x10-5 min-1
2.45x10-5 min-1
12 µm
12 µm
Vinyl, Comm Crpt
10-5-10-4 m-1
Resitl carpet
10-3-10-2 m-1
mg/(min.pr)
PM2.5
1.27x10-1
3.05x10-1
2.00x10-2
2-3 µm
2-3 µm
PM5
4.93x10-1
5.45x10-1
1.00x10-1
NR - Not reported; assm - assumed
Allergen concentrations on home floors as well as allergen concentration in the air for
quiescent and disturbed conditions have also been measured and their ranges are represented
in Table 2 (Blay et al. 1997, Custovic et al. 1997, Custovic et al. 1999, Lidia and Salthammer
2003).
Table 2. Reservoir and air allergen concentration
However, the absence of controlled parameters in the experiments of previous studies limits
their application in the health risk assessment. Environmental conditions, such as humidity,
were rarely considered or controlled to isolate their importance in particle resuspension.
Systematic parametric variation, such as floor type, dust type and load, contaminant
concentration in dust load, have not been performed, leading to difficulties in interpreting
available data. Although it is generally accepted that floor disturbance mechanisms are
mechanical, aerodynamic and electrostatic in nature, there is no consensus, explanatory theory
for particle resuspension that can predict the effects of floor surface disturbances on particle
re-entrainment.
This report describes the development of an experimental and analytical methodology to
examine particle surface-to-air aerosolization when reservoirs are subjected to human-related
disturbances. The purpose is to establish a data bank detailing particle resuspension as a
function of floor vibrations and transient near surface air flows, characteristic of human
walking. This methodology was tested by conducting a set of resuspension experiments using
carpet and linoleum flooring loaded with reference quartz and German roach dusts.
RESUSPENSION CHAMBER METHOD
Experiments are conducted in a constructed experimental chamber (400x200x200 mm) with
temperature and relative humidity control. Dust samples are prepared containing various types
of allergen (Bla g 1, Bla g 2, Der p 1, Der p 2, Can f 1 and Fel d 1) separated into precise
particle size (8 bins from 0.4 to >9.0 µm) and allergen concentration ranges. The prepared
dust is uniformly deposited on typical building floor samples (size: 90x90 mm) using
designed particle disperser equipment. The selected surface samples are subjected to
computer controlled levels of aerodynamic and mechanical disturbances, simulating the
disturbance conditions associated with human walking. Resuspended particles are carried by a
particle-free cross air flow and sampled by both optical particle counters (Sensors Inc.,
Semtech PM-300) and a Cascade Impactor (Andersen Mark II, Series 20-800). This air flow
sample provides time resolved particle size distribution and size resolved samples to be tested
for allergen concentration using ELISA assay techniques (Chapman et al. 2000).
The aerodynamic disturbance was simulated with the impingement of six small air jets over
the flooring sample. To understand the walking-related airflow motion nearby the floor,
experiments were developed in a close environmental chamber using CO2 vapor released over
the floor (Gomes 2004). These experiments provided the range of horizontal air velocity and
the visualization of large scale air turbulence resulting from a human walking. The
mechanical disturbance was simulated with a system that replicates field collected floor
vibration data caused by human walking. Floor vibration acceleration generally falls between
0 and 5% of g (gravitational acceleration) with frequencies ranging from 4 to 20 Hz (Hurst
and Lezotte 1970, Chui and Smith 1988, Hanagan et al. 1996, Hanagan et al. 2003). However,
it is not uncommon to find accelerations higher than 70% of g (Hu et al. 1994). Electrostatic
built-up voltage caused by the shoes/floor interaction can reach values higher than 10,000
volts (Robinson-Hahn 1995) and can potentially interfere with surface-to-air particle
aerosolization, in particular organic or organic-containing material. This phenomenon is not
presently incorporated on this research, but will be include in the near future.
RESULTS
Calibrated quartz particles (Particle Technology Limited, Crushed Quartz #10, United
Kingdom) of known density, size distribution and composition are used to establish a basis of
comparison for resuspension behavior with laboratory-produced, German roach dust particles.
Two types of flooring, plastic carpet (100% olefin) and linoleum, were utilized. The floor
samples were uniformly loaded with ≈50 mg of the two types of dust. The temperature was
kept in between 26°C and 28°C and the relative humidity kept constant at 45%. Three sets of
floor disturbance were implemented: (1) floor vibration, (2) air puff and (3) combination of
both. For comparison, clean flooring samples were tested to the same set of disturbance and
revealed no particle resuspension. Figure 2 shows the vibration and aerodynamic floor
disturbance signal used.
Floor Disturbance Signals
Floor acceleration x 9.807 [m/s 2]
0.2
0.15
Person
approximating
Person
passing
0.1
Person
w alks aw ay
Air Puff
Floor
Vibration
0.05
0
-0.05
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
Tim e (sec)
-0.1
-0.15
-0.2
Vibration
-0.25
Vibration
&
Air puffs
Vibration
Figure 2. Floor vibration and air puff disturbance signals
The dust utilized had the characteristics represented on Table 3.
Table 3. Quartz and German roach dust properties
The disturbance lasted 10 minutes, but significant particle resuspension occurred only for the
first two minutes. After the disturbance had begun, a practically instantaneous burst of
resuspended particles was observed. As the disturbance continues, the resuspended particle
count decreased exponentially for about two minutes, returning to the chamber background
particle concentration values. Beyond the second minute, even with dust over the floor
samples, there was little further particle resuspension. Figure 3 shows the peak and average
resuspension factors (RF) and rates (RR) measured.
1.0E-02
1.0E-04
Quartz-Carpet
1.0E-05
Quartz-Linoleum
1.0E-06
Roach-Carpet
1.0E-07
Roach-Linoleum
Peak RR [min -1]
Peak RF [m -1]
1.0E-03
1.0E-08
Quartz-Carpet
1.0E-04
Quartz-Linoleum
1.0E-05
Roach-Carpet
1.0E-06
Roach-Linoleum
1.0E-07
Vibration
Air-puff
Vib+Air
Vibration
1.0E-04
Air-puff
Vib+Air
1.0E-03
1.0E-05
Quartz-Carpet
1.0E-06
Quartz-Linoleum
1.0E-07
Roach-Carpet
1.0E-08
Roach-Linoleum
1.0E-09
Avg RR [min-1]
Avg RF [m-1]
1.0E-03
1.0E-04
Quartz-Carpet
1.0E-05
Quartz-Linoleum
1.0E-06
Roach-Carpet
1.0E-07
Roach-Linoleum
1.0E-08
Vibration
Air-puff
Vib+Air
Vibration
Air-puff
Figure 3. Peak and average RF and RR Results
Vib+Air
The average RF and RR are values integrated over every second of the measuring period for
two minutes after the disturbance started. The peak RF and RR are values determined for the
period of one second when the highest particle concentration was observed by the OPC.
DISCUSSION AND CONCLUSIONS
Peak RF and RR measured in these experiments ranged from 10-6 to 10-3 m-1 and 10-5 to 10-2
min-1, while average RF and RR ranged from 10-8 to 10-4 m-1 and 10-7 to 10-3 min-1,
respectively. Despite the four order of magnitude range, these values fall between field
measured values found in the literature review.
The main observations derived from the experiments performed were: (1) for a continuous
disturbance, resuspension was only observed during the first two minutes with an initial burst
of particle reentrainment followed by an exponential decrease to undetectable value; (2) airpuff disturbances had a much higher impact on dust resuspension than the vibration
disturbances; (3) particles were more easily resuspended from linoleum flooring than from
carpet flooring; (4) German roach dust was more easily resuspended by air streams than
quartz dust.
The methodology presented has been demonstrated and proven to be a valuable tool to gather
reliable information on particle resuspension. The controlled environmental and disturbance
conditions, the flexibility to generate different types of disturbances (including a future
electrostatic disturbance), the broad range and flexibility of air sampling, the flexibility to use
different flooring and different dust such as allergen containing dust and surrogate CBW dusts
make it a potential useful tool for particle resuspension research and thereby contribute to the
development of exposure risk models.
ACKNOWLEDGEMENTS
The authors thank the Pennsylvania State University Institutes of the Environment and the
Indoor Environment Center for financial support.
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