RESUSPENSION OF ALLERGEN-CONTAINING PARTICLES UNDER MECHANICAL AND AERODYNAMIC DISTURBANCES FROM HUMAN WALKING

Transcription

1 RESUSPENSION OF ALLERGEN-CONTAINING PARTICLES UNDER MECHANICAL AND AERODYNAMIC DISTURBANCES FROM HUMAN WALKING C. Gomes 1, J. Freihaut 1,, W. Bahnfleth 1 1 Indoor Environment Center, Architectural Engineering Department Pennsylvania State University University Park, PA 16802, USA Abstract The number of people suffering from asthma in developed countries has doubled in the past 20 years. 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 significant fractions of populations in North America, Europe, and Japan. In the U.S., asthma related deaths are in excess of 5000 per year for the ~6% of the population having the disease. Health care and productivity related costs due to distress and lost time are in excess of $12 billion per year in the United States. Indoor allergen related diseases are believed inhalation sensitized and developed, suggesting an aerobiological pathway of allergen-containing carrier particles from reservoir to occupant respiration. But these pathways are not well understood or quantified. 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 distributions 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. Corresponding author. Tel.: ; fax: address: jfreihaut@engr.psu.edu@psu.edu (J.D. Freihaut). 1

2 Keywords: Particle resuspension, Human activity, Allergens, Bio-aerosols, Asthma 1. 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, approximately 5-6 % of all Americans suffer from asthma and approximately 5000 people die each year of asthma related complications. The economic burden of this illness in the United States is estimated at $12.7 billion dollars per year (Anonymity 2005). Symptoms of asthma may be triggered in genetically predisposed individuals and developed in non-atopic individuals by exposure to allergens. Common indoor allergens are specific protein structures associated with cat and dog fur and saliva, cockroach and dust mite droplets and body parts, mice urine, as well as some fungi. These sources contribute allergens to the reservoir dusts of building surfaces, either as standalone particulates or, upon disintegration, as adherents to inert dust particles in carpets, upholstery, and other reservoir surfaces. When disturbed and aerosolized by human activity the contaminated reservoir dusts release carrier particles containing allergens available for inhalation exposure, sensitizing and developing asthma in susceptible individuals. Allergen concentrations on home floors as well as allergen concentrations in the air for both quiescent and disturbed conditions have been measured and their ranges are represented in Table 1 (Custis et al. 2003; Custovic et al. 1997; Custovic et al. 1996; Custovic et al. 1998; Custovic et al. 1999a; Custovic et al. 1995; Custovic et al. 1999b; Custovic 1998; de Blay et al. 1991; de Blay 1991; de Blay et al. 1997; Platts-Mills et al. 1986; Platts-Mills 1996; Tovey et al. 1981; Woodfolk 1993). A comprehensive examination of the literature dealing with indoor allergen 2

3 exposures from personal exposure and monitoring perspective is reported by O Meara and Tovey (O'Meara 2000). However, difficulties in assessing airborne levels of specific allergens in buildings containing significant allergen concentrations in dust reservoirs has made establishing inhalation risk factors difficult. Consequently, risk factors for sensitization and disease development are based on allergen concentrations in reservoir dusts only, as indicated in Table 2. The lack of understanding of the aerobiological pathways and controlling aerosolization parameters and how these vary with indoor allergen type and particle size is of considerable significance: "At present the question of how allergen particles enter the lungs is not resolved, and this issue is of considerable importance since it may well define the distribution of "inflammation" and airway obstruction." (NAS 2000) " the threshold measurement proposed...was for the maximum concentration of...allergen in dust samples...clearly, this is not a measurement of the allergen entering the respiratory tract, but it appears to be the best index of exposure. (Platts-Mills 2000) and, It is difficult to know the relationship between such measurements (reservoir allergen concentrations) and what is actually deposited in the upper and/or lower respiratory tract of an individual. (O'Meara 2000) Developing an understanding of the phenomena behind human-activity induced aerobiological resuspension of allergens is of significance. 3

4 Initial studies examining the impact of human activity on particle resuspension were conducted in the 1960 s with radioactive dusts deposited on the floor of nuclear facilities. The resuspension factors from these and more recent studies were summarized by the US Nuclear Regulatory Commission (NRC 2002) and values ranged from 6x10-8 to 7x10-4 m -1. Sehmel (Sehmel 1980) presented a summary of particle resuspension factors caused by mechanical disturbances 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 and extrapolated resuspension factors from the nuclear material studies had limited application. Due to the increase of indoor dust-related respiratory diseases, as well as the emergence of actual and potential attacks on civilian populations in which the use of aerosol or particulate delivered contaminants are employed, several studies on indoor particle resuspension have been performed (Buttner 2002; Ferro 2004; Hambraeus et al. 1978; Karlsson 1999; Karlsson 1996; Matsumo 2003; Thatcher 1995; Weis 2002). Table 3 summarizes relevant findings. However, the field study nature of many of the investigations limited the investigators ability to systematically vary parameters. Environmental conditions, such as humidity, were rarely considered or controlled to isolate and systematic parametric investigations - floor type, dust type and load, contaminant concentration in dust loads - have been quite limited, leading to difficulties in interpreting limited data. Laboratory studies with microbes have also been limited (Buttner 2002; Karlsson 1999; Karlsson 1996), making it difficult the developing of mitigation strategies. 4

5 This report describes the development of an experimental and analytical methodology to examine particle surface-to-air aerosolization from reservoirs subjected to human-related disturbances. The purpose is to establish a data bank detailing particle resuspension as a function of floor vibrations, transient air flow disturbances of reservoirs and transient electrostatic fields caused by human activity, such as walking. The methodology was tested relative to vibration and aerodynamic particle reservoir disturbances by conducting a set of resuspension experiments using carpet and linoleum flooring loaded with reference quartz particles, Bacillus Subtilis spores, and laboratory produced roach and dust mite allergen carrier particles produced from natural sources - roach fras and spent dust mite culture. 2. Experimental methodology Experiments were conducted in a laboratory experimental chamber (400x200x200 mm) with temperature, relative humidity and supply air particulate control. Typical indoor linoleum and carpet, 9x9 cm, flooring samples were uniformly loaded with a concentration of particles of known size and contaminant distribution. The selected surface samples are subjected to computer controlled levels of aerodynamic air-swirls and field measured, walking-induced mechanical vibration disturbances, simulating the disturbance conditions associated with human walking. Resuspended particles are carried by a particle-free, sweep flow, monitored by an optical particle counter to provide time resolved particle size distribution Floor disturbance reproduction Due to the lack of understanding of the effect of human walking on particle resuspension, it is desirable to isolate each gait-induced disturbance (mechanical, 5

6 aerodynamic and electrostatic) to the degree possible to determine their respective impact. Building floor vibration acceleration generally falls between 0 and 5% of g (gravitational acceleration) with frequencies ranging from 4 to 20 Hz (Chui 1988; Hanagan 2003; Hanagan 1996; Hu 1994; Hurst 1970). Levels higher than 70% of g, however, have been reported (Hu 1994). Although not large enough to overcome particle weight, such vibration frequencies may be sufficient to induce a lift-off drag force vector which breaks particle surface adhesion, making particles susceptible to convection by local, turbulent eddies introduced by footsteps. A simple drag force analysis on ideal spherical particles under Stokes regime reveals that vibration induced vertical motion causes a drag force of the same magnitude of weight force for 10 µm particles and 3 orders of magnitude higher for 0.3 µm size particle. Thus, although surface vibration is insufficient in itself for particle resuspension it can play an initiator role in human-activity caused particle resuspension. The mechanical vibration disturbance of the floor was simulated with a system that reproduces field collected floor vibration data caused by human walking. The system, controlled by a LabView control and data acquisition system (vs. 7.1), generates the desired controlled vibration signal which, after being amplified (Wilcoxon Amplifier-PA7F), is reproduced by a Wilcoxon F4 shaker. The vibration generated is calibrated with an accelerometer (PCB 393A03) which transmits a signal to a Siglab system (DSP Technology, Inc, model 20-22) to be monitored. To understand the walking-related airflow motion and induced swirls near the floor, experiments were developed in a close environmental chamber using CO 2 6

7 vapor released over the floor (Gomes 2004). Large scale eddies, as lit by a florescent visible light, were cm in diameter and horizontal air velocity topped at m s -1. Although difficult to reproduce an exact representation of the air stream/turbulence pattern visualized, these observations permitted the simulation of the gait induced aerodynamic disturbance. The observed swirl simulation was achieved with the impingement of six, 45 inclined, small air jets positioned around and over the flooring sample in the test chamber, which induced an average horizontal air velocity of 1.5 m s -1 as measured with hot-wire anemometer (Solomat 510e/127MS). Electrostatic voltage built up by shoe-floor tribology interactions can reach values higher than 10,000 volts (Robinson-Hahn 1995) and can potentially interfere with surface-to-air particle aerosolization, in particular on electrostatic susceptible organic based material. This phenomenon, to be incorporated in future research, is believed to have an important role on indoor particle resuspension process for some particle types. Figure 1 shows the mechanical and aerodynamic floor disturbance signal used. The 16 second, vibration and air swirl signals, is divided into three phases. The first phase simulates a person walking towards a particular floor location while sufficiently far away as to not cause any airflow disturbance at the particle reservoir. In this stage, only the vibration signal is activated. In the second phase, which lasts from second s four to five, the signals simulate the person passing over the floor particle reservoir location, perturbing the dust-containing reservoir surface both mechanically and aerodynamically. Therefore, both disturbance signals are activated. In the third phase, the person walks away and, as in the first 7

8 phase, only vibration is transmitted to the floor location and only the mechanical signal is activated. The amplitude of the mechanical signal can be altered, achieving different acceleration intensities Sampling Sampling was performed by an optical particle counter (Sensors Inc., Semtech PM- 300) that monitors scattered light for seven particle size bins in the 0.3 µm to 2.0 µm range and counts all particles greater than 2.0 µm as one bin. This system allows for the determination of resuspension rates by counting the number of particles resuspended from the floor by unit of sampled air volume and for each size bin. Resuspension rate (RR) is then found as the fraction of a surface species removed in unit time. 2 1 surface removal rate (# /( m.min)) RR (min ) = 2 surface concentration (# / m ) The peak resuspension rates presented in this report are values determined for the period of one second when the highest particle concentration was observed. The average resuspension rates are values integrated over every second of the measuring period for two minutes Allergen carrier particle dusts from parent source materials Roach allergen carrier particles were produced from German cockroach fras associated with a roach colony. Bla g 1 and Bla g 2 are common allergens, among others, associated with German cockroaches. Dust mite carrier particles were produced from spent dust mite culture provided by Dr. Martin Chapman of Indoor Biotechnologies Corporation. Specific milling and sieving sequences are followed in preparing the dusts. The allergen containing powders, once produced, are particle size characterized via optical particle counting and impactor train 8

9 separation techniques. Specific allergen contents of the different carrier particle size cuts are determined by enzyme linked, immunoassay techniques (ELISA) (Chapman 2003). The roach and mite allergen carrier particle powders are part of a more extensive sample bank of allergen carrier particles which include dog and cat allergen carrier particles. The purpose of the sample bank is to have sufficient amounts of reservoir dusts of known particle size, allergen content, surface and tribology properties to, enabling systematic investigations of resuspension behavior, filtration properties, and allergen denaturing approaches for different allergen carrier particles. The particles are prepared from concentrated fras, fur or culture source materials to insure allergen levels in produced particles are relatively constant and of sufficient levels to be determined straightforwardly by ELISA techniques. Allergen levels in dust samples collected directly from building reservoirs are quite variable from location to location, vary with particle size distribution of a particular location, and many times are of such low levels in the integrated dust samples that allergen determinations have significant uncertainties. 3. Experiments and results On a first set of experiments 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, exterior plastic grass carpet (100% UV stabilized olefin) and linoleum, were utilized. The floor samples were uniformly loaded with 50 mg ( 6.2 g m -2 ) of dust. During resuspension experiments, the temperature was kept between 26 C and 28 C and the relative humidity kept constant at 45%. Three sets of floor 9

10 disturbance were implemented: (1) floor vibration (peak of 20% of g), (2) air swirl (1.5 m s -1 horizontal air velocity) and (3) a combination of both. For comparison, clean flooring samples were tested to the same set of disturbance and revealed no particle resuspension. The dust utilized had the characteristics represented on Table 4. Resuspension rates were only determined for particles bigger than 2 µm. The disturbance was repeated continuously for a total of 10 minutes. 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, gradually returning to the chamber background particle concentration values. Beyond the second minute, even with dust remaining in the floor samples, there was little further particle resuspension. Figure 2 shows a typical profile of a time resolved air particle concentration curve during a resuspension experiment. Figure 3 shows average and peak resuspension rates determined for all the 12 possible combinations of dust type, floor type and disturbance, on a one replication setting experiment. Average resuspension rates measured in these experiments ranged from 10-7 to 10-3 min -1 while peak resuspension rates ranged from 10-5 to 10-2 min -1. Despite the four order of magnitude range, these values fall between field measured values found in the literature review. 10

11 An analysis of variance (statistic package: Minitab 14) showed a significant impact of air-swirl disturbance (p-value=0.000), floor type (p-value=0.019) and dust type (p-value=0.001); and no significant effect for the vibration disturbance (pvalue=0.984) on particle resuspension rates. Air-swirl disturbances impacted particle resuspension one to three orders of magnitude greater than the vibration disturbances. Resuspension rates for linoleum were greater than for carpet for both quartz and roach dust, with one order of magnitude difference for the quartz particles. This observation may be explained by the higher exposure of the dust to air streams flowing over the linoleum smoother surface as compared to the obstructed fibrous carpet flooring. For the same type of disturbance, the roach dust resuspension rates were times greater than the resuspension rates for the quartz dust. This higher rate of resuspension may be explained by the smaller density of the roach particle (d 1) compared to the quartz dust (d=2.65) and/or by the chemical and electrostatic properties of these two different dusts. Instant resuspension rates were in general 10 to 100 times higher than their respective average values. A second set of experiments included dust mite, Bacillus Subtilis spore dust (an anthrax simulant) and standard reference quartz. The dust mite powder was milled and sieved to a size distribution of 70% above 10 µm and 30% below 10 µm as revealed by an Andersen cascade impactor train. The optical particle counter measurements ( µm and bigger than 2.0 µm) are shown on Table 5. Screening 2k factorial experiments (Montgomery 2005) were designed to identify the main factors impacting particle resuspension. The factors and levels were selected (Table 6) based on previous research. Due to the screening nature of these experiments, not all of the 64 runs (2 6 ) were needed. A fractional factorial analysis 11

12 (2 6-2 ) was adequate and enabled collection of information on the main effects that would be obtained from running all 64 experiments. Dust mite and spores were compared to quartz in two independent sets of statistical 2k factorial, 16-runs experiments. The disturbance was again repeated continuously to last a total of 10 minutes. Resuspension occurred only for the first two minutes and air particle concentration curve was similar to the one shown on Figure 2. Table 7 shows the p-values for the quartz & dust mite experiments, reflecting the impact of each factor on resuspension rate for the eight different particle size bins. Air swirl intensity impacted significantly on resuspension (confident level <5%) for all particle size below 2 µm and even marginally for particles above 2 µm. Dust load (0.5 g m -2 vs. 2.5 g m -2 ) marginally impacted resuspension (confidence level of <13%) for all particle sizes below 2 µm. Table 8 shows two minute averaged resuspension rates for low and high level of air swirl intensity and dust load. Resuspension rates peak values were, in general, one order of magnitude higher than the respective two minutes average value. There is a direct relationship between resuspension rate and air velocity as suggested by Figure 4. Resuspension rates are consistently higher for higher level of air swirl intensity by one to two orders of magnitude. Alternatively, there is a reverse relationship between resuspension rate and dust load. Here, resuspension rates are consistently lower (up to one order of magnitude) for higher levels of dust load. As the dust load increases, the ratio of particles resuspended from the 12

13 available dust load on the surface tends to decrease. Nevertheless, it is observed that more particles are resuspended for higher dust loads. Figure 4 does not reference particle type, floor type, humidity and floor vibration intensity. No general consistent significance was detected for these factors and, therefore, the curves were averaged over these factors. Dust type (quartz vs. dust mite) impacted resuspension rate for some particle sizes but not for others. The resuspension rate was in general smaller for dust mite particles. This observation is distinct from the previous roach dust observations when the lighter roach particles were observed to be resuspended easier than the heavier quartz particles. Floor type showed a slight impact on resuspension for particle size µm but not enough consistency is observed with the other particle sizes. Vibration (2% vs. 60%) and humidity (40% vs. 70%) had no significant impact on resuspension of these particle types. The second factorial analysis was performed with a different organic material (spore material instead of dust mite) and same organic standard reference quartz dust. All the other factors (air swirl, floor type, dust load, vibration and humidity) were kept the same and at the same levels. Table 9 shows the p-values for the quartz & spores experiments. As before, air swirl level continues to significantly impact resuspension (confident level <0.5%) for all particle sizes, including particles bigger than 2 µm. Again, 13

14 there is a direct relationship between resuspension and air swirl velocity as was observed on Table 8 and Figure 4. Dust type (quartz vs. spores) and floor type (linoleum vs. carpet) showed a marginal impact on resuspension (confident level of <20%) for some particle sizes. Resuspension was more evident for spores particles and carpet flooring when compared with quartz and linoleum. The former observation is qualitatively consistent with the quartz-roach experiments observations, where resuspension was more evident for roach particles. Dust load (0.5 g m -2 vs. 2.5 g m -2 ) did not show a consistent and significant effect on resuspension as it did during the quartz-dust mite experiments. In the two cases that dust load had a marginal impact on resuspension ( µm and µm), an opposite relation-ship was observed: resuspension rate was higher for higher surface dust load. Consistent with previous observations, vibration did not show any significant impact on particle resuspension. The relative humidity (40% vs. 70%) showed no significance for particle size smaller than 2.0 µm. However, some effect was observed for particle size bigger than 2 µm with the tendency to increase resuspension for higher humidity levels. Table 10 shows two minutes averaged resuspension rates. As before, the resuspension rates peak values were, in general, one order of magnitude higher than the respective two minutes average value. 14

15 Figure 5 (top) shows a consistent direct relation-ship between resuspension and air swirl velocity. Figure 5 (bottom) shows that, for all particle sizes, resuspension rates were higher for carpet than linoleum. This observation disagrees with those from the quartz-roach experiments, where resuspension was higher for linoleum. The reason is not totally understood. A possible reason may be related to differences in carpet material fibers. The former used exterior cut low pile grass carpet and the latest used interior low pile carpet. The grass carpet had larger fibers and could provide larger surfaces for particle adhesion than the much smaller fibers of the interior carpet. Nevertheless, this topic needs to be further investigated. As it was noticed for the quartz-dust mite experiments, the resuspension rates were higher for the particle size range between 0.3 and 0.39 µm. A cross-comparison between the two sets of experiments (quartz-dust mite and quartz-spores) performed at the risk of going beyond the scope of these two 2k analysis, reveals the relative higher resuspension rates for spores compared to dust mite for all particle sizes (Figure 6). These rates were determine for 1.5 m s -1 air swirl intensity (higher level) and averaged for all other factors. The combination of both data sets resulted in no evidence of any other significant factors besides air swirl velocity. Resuspension rates for spores are consistently higher than dust mite and quartz across the whole particle size spectrum. The reasons for the almost two orders of magnitude difference between spores and dust mite resuspension is still not understood. Scanning microscope images show no significant difference on particle shape for both dusts and, with almost identical densities, the physical 15

16 properties of both dusts are very similar. This fact suggests that differences in surface electrical and/or chemical properties may be the reason for the distinct aerosolization behavior and should, therefore, be further investigated. Quartz is consistently less susceptible to be resuspended than spores but slightly more than dust mite. Since the density difference of quartz to the other dusts are very similar, the heavier weight of quartz does not seam to be a plausible reason for the distinct resuspension behavior. The fact that quartz resuspension rates situated in-between the values measured with dust mite and spores, suggests that there may also be a surface property and shape explanation for the differences in particle reentrainment behavior. 4. Discussion and conclusions An instrumented, controlled chamber is utilized wherein systematically varied induced floor vibration and air swirls are imposed on a reservoir surface previously loaded with a concentration of particles of known size and contaminant distribution. The imposed vibration and aerodynamic disturbances simulate those induced near a floor surface by walking. Air suspension of particles from the surface is tracked by particle-size resolved optical particle counter. 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. Peak particle resuspension rates were, in general, one order of magnitude higher than their respective average values. Average resuspension rates ranged from 10-7 to 10-3 min -1. Despite the four order of magnitude range, these values fall between field measured values found in the 16

17 literature review. More and systematic experiments are needed to determine more reliable data, with consequent comparison with field experiments. However, the values obtained are consistent with the literature data. Factorial and variance statistic analysis were applied to identify the factors that influence particle resuspension. The factors introduced were floor type, dust type, surface dust load, humidity and floor disturbance intensity (both vibration and air swirl). Consistent in all the experiments performed, air swirl intensity, induced by six air swirlers over the samples, was the major factor influencing particle resuspension, with two orders of magnitude different between 0.4 m s -1 and 1.5 m s -1 air velocity. German roach allergen containing dust particles were more easily resuspended than quartz dusts, believed due to lower particle density. Bacillus Subtilis spore dust particles revealed higher resuspension rates than dust mite allergen containing particles for the same conditions, which may be explained by differences in particle surface properties. Aside from the differences in roach and quartz dusts, dust type differences generally showed only marginal impact on resuspension. Dust loading showed some significance when quartz and dust mite were compared, having an inverse influence on resuspension rates, decreasing for higher loads of dust. Although of some significance, the floor surface type influence was unclear and needs further systematic investigation. Vibration levels were both below gravitational acceleration and, alone, had little effect on particle re-suspension to the bulk sweep flows. Nevertheless, vibration is a factor that should not be discarded since it appears to play a significant role in 17

18 initiating particle dislodging, a condition necessary for particle resuspension into bulk flows. The 30% difference on the relative humidity did not cause any noticeable variation on particle resuspension. Since no humidity effect was observed for these type of particles, wherein no transient electrostatic field disturbance is included, humidity does not induce capillary film surface adhesion in the given humidity range. The effect of particle residual charge as well as the effect of differences in tribologyrelated properties of particles, reservoirs and clothing on particle resuspension behavior when subjected to transient electrostatic field disturbances are to be investigated in future experimental configuration. In conclusion, the laboratory methodology presented here has been demonstrated to be a useful tool to gather reliable information on particle resuspension. The controlled environmental and disturbance conditions, the flexibility to generate different types of disturbances (including future electrostatic disturbances), the flexibility to use different flooring and dust types, such as allergen containing dust and surrogate CBW dusts make it a potentially useful tool for particle resuspension research and development of exposure risk models of resuspension. Acknowledgements The authors thank the Pennsylvania State University Institutes of the Environment and the Indoor Environment Center for financial support. 18

19 References Anonymity, Center of Disease Control and Prevention, Department of Health and Human Science, Asthma: data and surveillance, ASHRAE, Thermal Environmental Conditions for Human Occupancy. ANSI/ASHRAE Standard Buttner, M. P., Cruz-Perez, P., Stetzenback, L.D., Garrett, P.J., Luedtke, A.E., Measurement of airborne fungal spore dispersal from three types of flooring materials. Aerobiologia 18, Chapman, M. D., Pediatric Allergy: Principles and Practice, Indoor allergens. Elsevier Science. Chui, Y. H., Smith, I., A serviceability criterion to avoid human discomfort for lightweight wooden floors. Symposium Workshop on Serviceability of Buildings, Ottawa, Custis, N., J. Woodfolk, J. Vaughan and T. Platts-Mills, Quantitative measurement of airborne allergens from dust mites, dogs, and cats using an ion charging device. Clinical and Experimental Allergy 33(7), Custovic, A., R. Green, A. Fletcher, A. Smith, A. C. Pickering, M. D. Chapman and A. Woodcock, Aerodynamic properties of the major dog allergen Can f 1: distribution in homes, concentration, and particle size of allergen in the air. American Journal of Respiratory and Critical Care Medicine 155,

20 Custovic, A., R. Green, S. Taggart, A. Smith, C. Pickering, M. Chapman and A. Woodcock, Domestic allergens in public places II: dog (Can f 1) and cockroach (Bla g 2) allergens in dust and mite, cat, dog and cockroach allergen in the air in public buildings. Clinical and Experimental Allergy 26, Custovic, A., A. Simpson, H. Pahdi, R. Green, M. Chapman and A. Woodcock, Distribution, aerodynamic characteristics, and removal of the major cat allergen Fel d 1 in British homes. Thorax 53(33-38). Custovic, A., B. Simpson, A. Simpson, C. Hallam, M. Craven and A. Woodcock, 1999a. Relationship between mite, cat, and dog allergens in reservoir dust and ambient air. Allergy 54(6), Custovic, A., S. Taggart, R. Niven and A. Woodcock, Evaluating exposure to mite allergens. Journal of Allergy and Clinical Immunology 96(1), Custovic, A., H. Woodcock, M. Craven, R. Hassall, E. Hadley, A. Simpson and A. Woodcock, 1999b. Dust mite allergens are carried on not only large particles. Pediatric Allergy and Immunology 10(4), Custovic, A. S., A., Pahdi, H., Green, R., Chapman, M., Woodcock, A., Distribution, aerodynamic characteristics, and removal of the major cat allergen Fel d 1 in British homes. Thorax 53(33-38). de Blay, F., M. D. Chapman and T. A. E. Platts-Mills, Airborne Cat Allergen (Fel d 1) - Environmental Control with the cat in situ. American Review of Respiratory Diseases 143,

21 de Blay, F., Heymann, P.W., Chapman, M.D. and Platts-Mills, T.A.E., Airborne dust mite allergens: comparison of group II allergens with group I mite allergen and cat allergen Fel d 1. Journal of Allergy and Clinical Immunology 88(6), de Blay, F., J. Sanchez, G. Hedelin, A. Perez-Infante, A. Verot, M. Chapman and G. Pauli, Dust and airborne exposure to allergens derived from cockroach (Blattella germanica) in low-cost public housing in Strasbourg (France). Journal of Allergy and Clinical Immunology 99(1), Ferro, A. R., Kopperud, R.J., Hildemann. L.M., Source strengths for indoor human activities that resuspend particulate matter. Environmental Science and Technology 38(6), Gomes, C. S., Resuspension of allergen-containing particles subject to mechanical and aerodynamic disturbance - introduction to an experimental controlled methodology. University Park, PA (USA), Pennsylvania State University. Hambraeus, A., S. Bengtsson and G. Laurell, Bacterial contamination in a modern operating suite. Importance of floor contamination as a source of airborne bacteria. Journal of Hygiene, Cambridge 80(2), Hanagan, L. M., Raebel, C.H.,Trethewey, M.W., Dynamic measurements of in-place steel floors to assess vibration performance. Journal of Performance of Constructed Facilities, ASCE, Hanagan, L. M., Rottmann, C. and Murray, T.M., Control of floor vibrations. Structures Congress XIV,

22 Hu, L., Smith, I. Chui, Y., Vibration analysis of ribbed plates with a rigid intermediate line support. Journal of Sounds and Vibration 178(2), Hurst, H. T., Lezotte, H.R., A comparison of vibrational characteristics of wooden floors. Building Science 5, Karlsson, E., Berglund, T., Stromqvist, M., Nordstrand, M, and Fangmark, I., The effect of resuspension caused by human activities on the indoor concentration of biological aerosols. Journal of Aerosol Science 30(Suppl1), S Karlsson, E., Fangmark, I. Berglund, T., Resuspension of an indoor aerosol. Journal of Aerosol Science 27(Suppl. 1), S441-S442. Matsumo, G., Anthrax powder: state of the art? Science 302, Montgomery, D. C., Design and Analysis of Experiments. Wiley. NAS, Clearing the air: asthma and indoor air exposures. National Academy Press, Washington, D.C. NRC, Re-evaluation of the indoor resuspension factor for the screening analysis of the building occupancy scenario for NRC's license termination rule (Draft Report for Comment), US Nuclear Regulatory Commission Office of Nuclear Material Safety and Safeguards. O'Meara, T. a. T., E., Monitoring personal allergen exposure. Clinical Reviews in Allergy and Immunology 18,

23 Platts-Mills, T. A., P. W. Heymann, J. L. Longbottom and S. R. Wilkins, Airborne allergens associated with asthma: particle sizes carrying dust mite and rat allergens measured with a cascade impactor. Journal of Allergy and Clinical Immunology 77(6), Platts-Mills, T. A. E., Indoor Air and Human Health, Estimation of allergen concentration in indoor environments: prediction of health-related effects. CRC Lewis Publishers, New York. Platts-Mills, T. A. E., Indoor Air Quality Handbook, Allergens derived from arthropods and domestic animals. McGraw-Hill, New York. Robinson-Hahn, D., ESD flooring: an engineering evaluation. Electrical Overstress/Electrostatic Discharge Symposium Proceedings, Sehmel, G. A., Particle resuspension: a review. Environment International 4, Thatcher, T. L., Layton, D.W., Deposition, re-suspension and penetration of particles withing a residence. Atmospheric Environment 29(13), Tovey, E., M. Chapman, C. W. Wells and T. Platts-Mills, The distribution of dust mite allergen in the houses of patients with asthma. American Review of Respiratory Diseases 124, Weis, C. P., Intrepido, A.J., Miller, A.K. Cowin. P.G., Durno, M.A. Gebhardt, J.S., Bull, R., Secondary aerosolization of viable bacillus anthracis spores in a contaminated US senate office. JAMA 288(22),

24 Woodfolk, J. A., et. al., The effect of vacuum cleaners on the concentration and particle size distribution of airborne cat allergen. Journal of Allergy and Clinical Immunology 91(4),

25 Figure Captions Figure 1: Floor vibration and air swirl disturbance signals Figure 2: Typical resuspended air particle concentration profile Figure 3: Average and peak resuspension rates Figure 4: Average resuspension rates [min -1 ] Figure 5: Average resuspension rates [min -1 ] Figure 6: Resuspension rates [min -1 ] 25

26 Table Table 1: Reservoir and air allergen concentration Allergen Origin Floor Air Quiescent Disturbed Bla g 1 German Roach 0-14,000 U g U m -3 Bla g 2 German Roach 0-2,000 U g U m -3 Can f 1 Dog µg g ng m ng m -3 Fel d 1 Cat µg g ng m ng m -3 Der p 1 Dust Mite µg g ng m ng m -3 26

27 Table 2: Risks relative to allergen concentration in reservoir dusts Risk of Sensitization Mite Group 1 Fel d 1 Can f 1 Bla g 1 Bla g 2 for Atopic Children µg g -1 µg g -1 µg g -1 U g -1 µg g -1 High > >8 >1 Medium Low <0.3 <0.2 or >20 <0.2 or >20 <0.6 <<0.08 (Chapman 2003) 27

28 Table 3: Summary of particle resuspension studies Source Experimental Ambient Settings Conditions Resuspension Particle Size Hambraeus Bacteria particles T=NR a 2.5x10-3 m µm et al. Hospital RH=NR a 2.0x10-4 m µm 1978 Vinyl floor Ventl=off 1.2x10-3 m µm No air leakge Thatcher Inert dust T=NR a 1.65x10-8 min µm et al. Residential Bldg RH=NR a 7.33x10-9 min µm 1995 Carpet, wood and 3.00x10-7 min µm vinyl floor 1.38x10-6 min µm 6.33x10-6 min µm 5.67x10-7 min -1 >25 µm Karlsson Experimental rm T=NR a 8.0x10-2 m µm et al. Grass Pollen RH=NR a 7.8x10-2 min µm 1996 NR floor Karlsson Experimental rm T=NR a 1.8x10-5 min µm et al. Freeze dried spores RH=NR a 2.45x10-5 min µm 1999 PVC floor Buttner Experimental rm HVAC, HEPA Vinyl, Comm Crpt et al. Penicillium Chr. 5 Pa pressz m µm 2002 Vinyl and carpet T=NR a Resitl carpet RH=NR a m µm Ferro Single family T 20 C mg (min.pr) -1 el al. NR dust RH=NR a PM2.5 PM Wood floor 1.27x x10-1 Rug 3.05x x10-1 a) NR - Not reported 2.00x x

29 Table 4: Quartz and German roach dust size and allergen distribution Quartz Dust [ρ=2650 Kg m -3 ] German Roach [ρ 1000 Kg m -3 ] Diameter [µm] Distribution Diameter [µm] Distribution Aerodynamic Optical Opt. Avg Mass Number Aerodynamic Optical Opt. Avg Mass Number % 0.72% >9.0 >9.0 > % 32.41% % 2.00% % 17.38% % 6.24% % 13.60% % 22.98% % 25.40% % 68.06% % 11.21% Bla g 1: 3930 U/g dust Bla g 2: 897 µg/g dust 29

30 Table 5: Quartz, dust mite and spores size distribution Quartz [ρ=2650 Kg m -3 ] Mite [ρ=1140 Kg m -3 ] Spores [ρ 1000 Kg m -3 ] Size [µm] Number Mass Number Mass Number Mass % 0.27% 15.42% 0.04% 11.53% 0.04% % 0.32% 27.53% 0.15% 18.65% 0.14% % 0.39% 13.11% 0.14% 15.35% 0.23% % 0.26% 9.36% 0.13% 15.13% 0.29% % 0.72% 13.31% 0.58% 17.93% 1.06% % 1.40% 4.57% 0.60% 7.97% 1.42% % 1.80% 3.62% 1.25% 4.07% 1.92% > % 94.84% 13.09% 97.11% 9.37% 94.90% 30

31 Table 6: Factors potentially impacting resuspension rate Factor Low level High level Air swirl 0.4 m s m s -1 Dust type Reference Quartz Mite or spores Floor type Linoleum Carpet (d) Dust load (a) 0.5 g m g m -2 Vibration (b) 2% g 60% g Humidity (c) 40% 70% Table notes: (a) The low level (0.5 g m -2 ) was taken from Thatcher and Layton (Thatcher 1995) for floor load measure in a California home. The high level was chosen to be half way from 0.5 g m -2 and the 6.2 g m -2 used on the preliminary quartz-roach dust resuspension experiments. (b) The low level is a typical building floor acceleration and the high level is a non-typical, but occasionally observed, short-term floor acceleration in wood frame floors. (c) Comfortable humidity levels ranges between 30% and 60% (ASHRAE 2004). For technical limitations it was not possible to drop the humidity level below 40% and this humidity is used as the low level. For the humidity high level it was used a higher than 60% since higher humidity levels are normally found in residential buildings. (d) Typical indoor low pile carpet (100% olefin). 31

32 Table 7: Resuspension rate p-values quartz vs. dust mite Particle size [µm] Air swirl Dust type Floor type Dust load Vibration Humidity > Note: p-values below (confident level <20%) are highlighted in bold font. 32

33 Table 8: Average resuspension rates [min -1 ] Particle size [µm] 0.4 m s m s g m g m g m g m E E E E E E E E E E E E E E E E E E E E E E E E E E E E-06 > E E E E-06 33

34 Table 9: Resuspension rate p-values quartz vs. spores Particle size [µm] Air swirl Dust type Floor type Dust load Vibration Humidity > Note: p-values below (confident level <20%) are highlighted in bold font. 34

35 Table 10: Average resuspension rates [min -1 ] Particle size [µm] 0.4 m s m s -1 Linoleum Carpet Linoleum Carpet E E E E E E E E E E E E E E E E E E E E E E E E E E E E-05 > E E E E-05 35