TY - JOUR
AU1 - Kokkonen,, Anna
AU2 - Väänänen,, Maija
AU3 - Säämänen,, Arto
AU4 - Pasanen,, Pertti
AB - Abstract Objective To shorten the time for airborne dust concentration to be reduced to a lower level after a renovation task has been completed, a short-term water misting method was assessed. A short-term water misting method is based on low water consumption to avoid harmful wetting of materials. The method is considered similar to a general ventilation method that dilutes work-generated airborne dust concentrations. Thus, short-term misting is not intended to replace the source control measures. Methods Airborne dust removal by the short-term water misting performed after dust generation was evaluated in a controlled laboratory settings by comparing PM10 decay and inhalable dust concentrations between a control and misting tests (average water flow = 0.22 l min−1) of 2 and 4 min. A portable handheld misting device was used. The practicability and effectiveness of the misting technique as a supplementary control measure was verified in the three field cases. Results In laboratory tests, reductions in airborne PM10 and inhalable dust were 30% and 28%, avoiding condensation of water to surfaces. In the field, inhalable dust concentrations were reduced by 86–95% after an hour from the misting, whereas ventilation alone was calculated to dilute dust concentrations by 18–39%. Average clean air delivery rates varied from 0.03 to 0.07 m3 s−1. Conclusions Short-term misting after a dust-generating task is an effective measure to control the airborne dust after dust-producing tasks in environments where an effective air exchange for dust removal is not a feasible alternative. The information obtained from the study is beneficial to construction and renovation project management personnel and field practitioners. construction, dust control, dust removal, inhalable dust, PM10 Introduction During construction and renovation works, particulate generation dynamics depend on several factors, for example, the characteristics of a processed material, work method, tooling, and the location of the dust emission (e.g. Tjoe Nij et al., 2003, 2004; Croteau et al., 2004; Flanagan et al., 2006; Akbar-Khanzadeh et al., 2010; Sauvé et al., 2013). High airborne dust concentrations are especially related to sawing and chipping tools, and grinders (Flanagan et al., 2006; Sauvé et al., 2013). In addition, particle size distributions vary between different task-based and tool-specific activities (Flanagan et al., 2006; Sauvé et al., 2013). When higher energy is involved, more particles and a smaller-scale size distribution are produced (World Health Organization (WHO), 1999). Thus, for example, surface grinding produces much greater dust emission due to a higher initial velocity than does drilling (Health and Safety Executive (HSE), 2017). Moreover, smaller particles are likely to disperse with air currents, especially when a task generates rapidly moving air streams (HSE, 2017). To prevent airborne dust release, water-based dust suppression techniques may be used in real time by wetting the material. However, conventional wet methods using running water have some disadvantages due to a high water consumption. These include safety issues, such as the risk of electric shocks, slurry formation, and slips caused by sludge (Croteau et al., 2004). Water misting on the tool alone or both material and tool during tasks has been suggested as a key dust control technique because it requires lower water flow rates and dries more quickly than running water (Brouwer et al., 2004; Beamer et al., 2005). However, some interior tasks are more susceptible to excess water spraying in real time. For example, the formation of slurry on the material is problematic in tuck-pointing, and water can leak into building structures, leading moisture damage (Beaudry et al., 2013). The control of airborne dust is difficult because fine particles can widely be dispersed via air currents within a construction site. Moreover, airborne dust particles may not be reduced below occupational dust exposure limit values despite the use of highly effective source control measures, such as on-tool local exhaust ventilation (LEV) during tasks (Meeker et al., 2009; Shepherd et al., 2009; Akbar-Khanzadeh et al., 2010; Carlo et al., 2010). When a dust-generating task is completed, some of the particles, nonetheless, remain airborne; here terminal setting velocity has a key role in particle removal in the absence of dust control measures. Particle removal by natural removal mechanisms alone is, however, very slow. By assuming spherical particles at normal temperature and pressure on a Stokes regime at room height of 2.5 m, gravitational settling time for particles of 1, 5,and 10 µm in diameter is over 23 h, 56 min, and 14 min, respectively. Large particles will settle more rapidly: e.g. particles of 25 and 50 µm diameter settle in 133 s and 33 s, respectively. To shorten the time for the dust concentration to be reduced to a lower level, a short-term water misting method was assessed in this study. The method is applied only after the work has been completed, and it is considered similar to a general ventilation method that dilutes the work-generated airborne dust concentrations. Thus, short-term misting is not intended to replace the source control measures. In the water misting technique, airborne dust particles can be collected by a moving water droplet as a result of inertial impaction and interception. However, water droplets do not come to contact with all dust particles with different sizes (Charinpanitkul and Tanthapanichakoon, 2011). The occurrence of a water droplet and particle collision depends on the size of the water droplet and the particle, their velocity difference, and their relative locations (Seinfeld and Pandis, 1998). A previous water spray study showed that a nozzle spray system delivering water droplets of 30–320 µm (average ~100 µm) had a total dust removal efficiency of 22–24% (Charinpanitkul and Tanthapanichakoon, 2011). The average dust particle size was 5 µm (range 2–10 µm). However, this finding was based on spraying water in real time during the dust generation. Fixed spray systems have also been used after dust generation in experimental water spray studies by Organiscak and Leon (1994), and Pollock and Organiscak (2007); both studies showed that the fixed systems could be effective in capturing airborne dust. With a short-term 3-min misting period after the dust generating was completed, the respirable dust concentration decreased ~70–90% from the reference concentration (Organiscak and Leon 1994). However, this finding may be an overestimation because the concentration decay curves of spray tests were not compared to a control decay without the spraying. Fixed water spray systems may not be practical to use in construction and renovation sites due to constantly changing work locations and tasks. Therefore, this study aims to evaluate the potential of short-term water misting with a portable handheld device to reduce airborne dust concentrations after dust-producing renovation tasks have been completed. First, the airborne dust removal was assessed through controlled laboratory tests. Laboratory tests were aimed at low water consumption to avoid harmful wetting of materials and safety risks related to running water techniques. Second, the practicality and effectiveness of the misting technique in dust control were verified in the field tests during actual renovation tasks. Materials and methods The evaluation of airborne dust reduction through short-term water misting was conducted in laboratory and field experiments by comparing PM10 decay and inhalable dust concentrations between the control and misting tests. PM10 as a smaller particle size fraction was chosen to monitor in real time to allow rapid observations on the effects of the short-term water misting on particle concentrations. It has been shown that dust particles generated from construction processes are largely in the inhalable size range rather than the respirable mass fraction (Shepherd et al. 2009). Therefore, inhalable dust was also measured to include the impact of short-term misting on larger particles. Water misting was performed with a handheld fogger B&G 2600 ULV Flex-A-Lite (B&G Equipment Company, Jackson, GA, USA). According to the instrument documentation, the droplet size can be adjusted to 20–35 µm or 56 µm; however, this was not measured. Distilled water at room temperature was used to avoid any optical measurement error during real-time particle monitoring regarding particles that may be contained in tap water. In control tests, the device was used without water to induce similar airflow as in the wet tests. This was carried out to obtain comparable air mixing between the control and misting tests. Laboratory tests Pretests were performed to optimize the water flow rate and misting period to avoid excessive wetting of surfaces. Pretests resulted in short, 2-min misting periods with on average water flow rate of 0.22 l min−1. In addition, 4-min misting periods were chosen to demonstrate the boundaries of misting time regarding the condensation of water to surfaces (i.e. achieving dew point). Laboratory tests involved control tests (N = 6), and misting tests with 2-min (N = 6) and 4-min (N = 2) water spray periods. The test room was an empty room (apart from test equipment) with dimensions 2.5 × 4.0 × 2.7 m (area 10 m2, volume 27 m3). The walls were made from gypsum board and the floors were tiled. The ventilation system removed the air via a wall-level exhaust in the upper part of the wall. The supply air was taken via door gaps. The air exchange rate averaged 0.3 ± 0.06 h−1 in the laboratory tests. The air exchange rate of each laboratory test was assessed by a tracer gas method where a tracer R134-a (1.1.1.2-tetrafluoroethane) was released into the test room and the concentration decay over time was monitored. Sampling was performed together with the analysis of tracer concentrations by the INNOVA 1303 Multipoint Sampler and Doser and 1412 Photo acoustic field gas monitor (LumaSense Technologies, Inc., Santa Clara, CA, USA). The air exchange rate was also evaluated from the relative humidity (RH) data obtained from the misting tests, being on average 0.3 h−1, similarly than that determined by the tracer gas method. However, the air exchange rates had a wider variation based on calculations from the RH data (0.05–0.9 h−1). RH was measured in real time with Hobo U12-013 (Onset Computer Corp., Bourne, MA, USA) with a logging interval of 10 s. Dust aerosol was introduced into the air at the center of the test room with a dust generator, Palas RBG 1000 (Palas GmbH, Karlsruhe, Germany), which can disperse a test powder in the range 0.1–100 µm diameter. The test dust used in laboratory tests was collected from the air with a portable construction site vacuum attached on-tool during concrete surface grinding. A mixing fan was used to disperse the generated dust into the test room air. Dust was generated for 45 min to obtain a concentration level (i.e. reference concentration) typical of construction tasks. Immediately after ending the dust emission, water misting of 2 or 4 min was performed. In the control tests, the misting device was used in the same manner as that in misting test, but only the airflow from the device was induced. Field tests Field tests were conducted at three renovation sites (Table 1) to trial the airborne dust reduction of the misting method in practice. Misting (average water flow rate 0.22 l min−1) was performed immediately after the dust-producing task was completed. A reasonable misting time (Table 1) was principally estimated based on the volumes of the rooms that were compared to the optimized misting period at the laboratory volume. Finally, the duration of misting was controlled by observation to avoid deposition of water to surfaces. Table 1. Study sites. Site Area (m2) Volume (m3) Misting time (min) Air exchange (h−1)a Task Tooling Concurrent tasks within the renovation site A 11 30 2 0.5 Surface grinding Handheld grinder with on-tool LEV No B 20 56 4 0.2 Concrete floor grinding and concrete drywall sanding Floor grinder with ventilation shroud, no LEV in drywall sanding Yes C 10 36 2 0.9 Concrete floor grinding Floor grinder with ventilation shroud Yes Site Area (m2) Volume (m3) Misting time (min) Air exchange (h−1)a Task Tooling Concurrent tasks within the renovation site A 11 30 2 0.5 Surface grinding Handheld grinder with on-tool LEV No B 20 56 4 0.2 Concrete floor grinding and concrete drywall sanding Floor grinder with ventilation shroud, no LEV in drywall sanding Yes C 10 36 2 0.9 Concrete floor grinding Floor grinder with ventilation shroud Yes LEV = local exhaust ventilation. aAir exchange rates in the field were calculated from the RH data obtained from the misting tests. View Large Table 1. Study sites. Site Area (m2) Volume (m3) Misting time (min) Air exchange (h−1)a Task Tooling Concurrent tasks within the renovation site A 11 30 2 0.5 Surface grinding Handheld grinder with on-tool LEV No B 20 56 4 0.2 Concrete floor grinding and concrete drywall sanding Floor grinder with ventilation shroud, no LEV in drywall sanding Yes C 10 36 2 0.9 Concrete floor grinding Floor grinder with ventilation shroud Yes Site Area (m2) Volume (m3) Misting time (min) Air exchange (h−1)a Task Tooling Concurrent tasks within the renovation site A 11 30 2 0.5 Surface grinding Handheld grinder with on-tool LEV No B 20 56 4 0.2 Concrete floor grinding and concrete drywall sanding Floor grinder with ventilation shroud, no LEV in drywall sanding Yes C 10 36 2 0.9 Concrete floor grinding Floor grinder with ventilation shroud Yes LEV = local exhaust ventilation. aAir exchange rates in the field were calculated from the RH data obtained from the misting tests. View Large In each study site, control and misting tests were carried out in the two similar-sized room next to each other (Table 1). At site B, test rooms were separated from other parts of the renovation area with plastic dust barriers at the doorways. In other sites, the test room doorways were not sealed. Test rooms of site C were more like open spaces, because they had two open doorways to adjacent rooms. Renovation sites were negatively pressurized against adjacent areas. Tools used with LEV were connected via flexible hoses to portable construction site vacuums with a HEPA filter to provide suction airflow for the tools. Portable LEV systems recirculated the filtered exhaust air back into the workspace. Air exchange rates of the test rooms were evaluated from the RH data of the misting tests, because the air exchange rates were similar in the laboratory tests according to the tracer gas method and RH measurement, although RH calculations were much more variable. While the accuracy of using RH to derive an air change rate is limited due to water evaporation, for our needs, an RH-based assessment gives a fair approximate of the real air change rate of the renovation sites studied. The air exchange was assumed to remain the same during the control tests. Measurements and data analysis PM10 particles The time-resolved mass concentration (mg m−3) of PM10 particles was measured with a DustTrak 8533 (TSI Inc., Shoreview, MN, USA) to assess the reference concentration (i.e. at the end of dust generation), dust decay of control and misting tests. A Diffusion Dryer 3062 (TSI Inc., Shoreview, MN, USA) was attached to the sampling line to minimize the optical measurement error of water mist. It was in use during both control and misting tests. The dust monitor was stationary, located at the center of the test room. In the field experiments, the dust monitor was placed close to dust-producing task. In the laboratory tests, the sampling duration was 90 min, and in the field, 67–111 min. The logging interval was 10 s. The detection limit of the dust monitor was 0.001 mg m−3. The results were corrected by the gravimetric sample (Mixed Cellulose Ester Membrane filter with a diameter of 37 mm and a pore size of 0.8 µm) collected by DustTrak 8533 (air flow 2.0 l min−1). The filters were dried in a desiccator 24 h before they were weighed under constant climatic conditions with static charge elimination. Three laboratory blanks were used to assess the weighing precision and limit of detection (LOD). LOD of the gravimetric analysis was determined as three times the standard deviation of the weight changes of the blank samples. All the samples were >LOD. The dust monitor was calibrated annually by manufacturers services (TSI Inc., Shoreview, MN, USA) prior to the measurements being taken. Inhalable dust Inhalable dust concentrations were assessed by collecting dust samples from the stationary sampling location with IOM-sampler (SKC Inc., Eighty Four, PA, USA). Dust samples were collected onto cellulose acetate filters (AAWP, diameter 25 mm, pore size 0.8 µm) by SKC 224 personal sampling pumps (SKC Inc., Eighty Four, PA, USA). The flow rate of the pumps was calibrated to 2.0 l min−1 prior the sampling. In the laboratory tests, one sampler was located 1.5 m from the dust-generating point and another sampler, 3 m from the dust-generation location. The latter sampling location was ~1.5 m away from the wall in which the exhaust ventilation device was positioned (upper level of the wall). Concentrations from the both sampling locations were calculated as mean concentration to obtain a representative concentration for the room air. During laboratory tests, dust samples were collected at the end of dust generation (i.e. the reference sample with 3-min sampling) and after misting (i.e. the dust decay phase). During the decay phase, inhalable dust samples were collected at four time points to observe dust decay and reduction in concentration over time. Sampling time points were 1–4, 6–11, 16–21, and 28–38 min from the end of the misting. Through preliminary testing, short sampling periods from 3 to 10 min were adjusted in the laboratory to suit the study purpose, although it is acknowledged that short sampling times are susceptible for sampling bias. In the field, one stationary sampler was placed ~1 m from the dust-generating task and inhalable dust sampling was carried out over the period of work activity (26 ± 12 min), and after water misting, for 60 min. The filters were dried in a desiccator 24 h before they were weighed under constant climatic conditions with static charge elimination. The balance used was capable of weighing to a precision of 1 μg. Two field blanks were used for every five samples collected. The LOD was determined in the same way as that described earlier for PM10. None of the field test samples was below LOD. However, laboratory tests had <LOD samples as follows: 3/60 (3%) of the control test samples, 6/60 (10%) of the 2-min misting test samples, and 6/20 (30%) of the 4-min misting tests. The values below the LOD were processed with NDExpo software (Flot 0.8.1, Montreal, Canada; http://www.expostats.ca/site/app-local/NDExpo/), which applies the robust regression on order statistics approach (Helsel, 2005). The software replaces the <LOD values with concentration estimates based on their rank among the set of detected values. The set of detected values used were separately for the control tests, misting of 2 min, and misting of 4 min. Dust reduction Decay concentrations were normalized with the reference concentration (i.e. the concentration prior the dust decay) for the calculations: NC= Ct, decayCreference , (1) where NC is normalized concentration (unitless), Ct, decay concentration during decay, and Creference concentration during dust generation. To assess how much PM10 and inhalable dust concentration had reduced (%) during misting tests, the normalized dust concentration ratio of misting tests (NCmisting) to control tests (NCcontrol) was determined: RRE=NC control−NC mistingNC control×100% , (2) where RRE is relative dust removal efficiency. For inhalable dust, the RRE was defined at the first time point after the misting period in the laboratory tests [equation (2)]. For the field tests, the RRE of inhalable dust was calculated over sampling period after the misting. Clean air delivery rate The efficiency of misting to reduce PM10 concentration was determined by the clean air delivery rate [CADR, (m3 h−1)]; Hak-Joon et al., 2012): CADR=V(kmisting−kcontrol) , (3) where V is the volume of the test room (m3), kmisting the decay rate obtained from misting tests (h−1) and kcontrol the decay rate (i.e. natural removal mechanisms) obtained from control tests (h−1). CADR results were also compared to the amount of water used. The decay rate k is the log-slope of the dust concentration decay curve, which is determined by the following equation (McCoy et al., 1985): k=lnC/C0t=−(Q/V+F/V) , (4) where C is the dust concentration (mg m−3) at time t (h), C0 the initial dust concentration (mg m−3), Q the ventilation flow (m3 h−1) through the test room, V the volume of the test room (m3), and F dust removal mechanisms (m3 h−1). Term Q/V is the decay rate (h−1) due to ventilating the chamber, and the term F/V (h−1) the sum of linear removal mechanisms, such as misting capture and background removal mechanisms of the test room including natural removal mechanisms. The sum of the terms Q/V and F/V are the (total) decay rate k. Results Relative humidity The mean RH during dust generation (the reference) and the misting phase is presented in Fig. 1A,B. In the laboratory, the RH increased on average 32%units with the 2-min misting periods, whereas the increase in RH was 47% units with the 4-min misting (Fig. 1A). Surfaces did not get wet with the shorter misting period. However, with 4-min misting, surfaces remained saturated over the dust sampling period. Similar water amounts were used in the laboratory and field experiments. With an elapsed 2-min misting period, the amount of water was 0.42 ± 0.09 l in the laboratory, and 0.39 l and 0.41 l in sites A and C, respectively. With a 4-min misting period, water was used 0.93 ± 0.05 l in the laboratory and 0.94 l at site B. After misting, the increase of RH compared to the reference value varied between 6.1 and 35% units in the field experiments (Fig. 1B). Materials did not get wet in the study sites. In theory (see Mollier diagram), the used water content during a 2-min misting in the prevailing laboratory conditions would have resulted in RH of 93%, somewhat higher than that observed in practice. Further, the maximum amount of water to avoid condensation to surfaces would be, in theory, ~0.5 l. In field experiments, the maximum amount of water to avoid wetting of materials would have been ~0.6 l in site A, 1.4 l in site B, and 0.7 l in site C. Figure 1. View largeDownload slide Relative humidity (RH; AM ± SD): (A) laboratory tests; (B) field experiments. Figure 1. View largeDownload slide Relative humidity (RH; AM ± SD): (A) laboratory tests; (B) field experiments. Dust reduction in the laboratory tests The water misting affected particle clearance during the misting and for a short period following that: the decay line is steeper during particle clearance (Fig. 2A). After that, the decay line changes to become parallel to the control decay line (slopes calculated to be 0.7 h−1 in these curves; Fig. 2A). Similar trend is shown for inhalable dust in Fig. 2B: the decay line is steeper between the reference and first decay sampling point than the decay line after that (for control and 2-min misting tests, slopes of 0.9 h−1 were calculated from curves between decay time points). In the test with 4-min misting periods (N = 2), the third and fourth decay points have uncertainty due to the <LOD samples. The reduction in normalized PM10 concentration was 30% and 62% with misting of 2 and 4 min, respectively (Table 2). Figure 2. View largeDownload slide Dust decays over time of control and misting tests in the laboratory: (A) PM10 (AM ± SD); (B) inhalable dust. Figure 2. View largeDownload slide Dust decays over time of control and misting tests in the laboratory: (A) PM10 (AM ± SD); (B) inhalable dust. Table 2. PM10 decay and reduction results in the laboratory and field. Test PM10 decay (h−1) Air exchange rate (h−1) NC [-] RRE of PM10 (%) Laboratory  Control 2.6 ± 0.7 0.3 ± 0.03 0.92 ± 0.02  Misting 2 min 10 ± 2.6 0.3 ± 0.05 0.65 ± 0.05 29.7  Misting 4 min 12 ± 0.6 0.4 ± 0.03 0.35 ± 0.02 61.8 Site A  Control 3.9 0.5 0.87  Misting 2 min 8.1 0.5 0.72 17.0 Site B  Control 3.2 0.2 0.82  Misting 4 min 7.5 0.2 0.57 28.9 Site C  Control 2.6 0.9 0.86  Misting 2 min 7.9 0.9 0.78 8.9 Test PM10 decay (h−1) Air exchange rate (h−1) NC [-] RRE of PM10 (%) Laboratory  Control 2.6 ± 0.7 0.3 ± 0.03 0.92 ± 0.02  Misting 2 min 10 ± 2.6 0.3 ± 0.05 0.65 ± 0.05 29.7  Misting 4 min 12 ± 0.6 0.4 ± 0.03 0.35 ± 0.02 61.8 Site A  Control 3.9 0.5 0.87  Misting 2 min 8.1 0.5 0.72 17.0 Site B  Control 3.2 0.2 0.82  Misting 4 min 7.5 0.2 0.57 28.9 Site C  Control 2.6 0.9 0.86  Misting 2 min 7.9 0.9 0.78 8.9 NC = normalized concentration [equation (2)]; - = unitless; RRE = relative dust removal efficiency. View Large Table 2. PM10 decay and reduction results in the laboratory and field. Test PM10 decay (h−1) Air exchange rate (h−1) NC [-] RRE of PM10 (%) Laboratory  Control 2.6 ± 0.7 0.3 ± 0.03 0.92 ± 0.02  Misting 2 min 10 ± 2.6 0.3 ± 0.05 0.65 ± 0.05 29.7  Misting 4 min 12 ± 0.6 0.4 ± 0.03 0.35 ± 0.02 61.8 Site A  Control 3.9 0.5 0.87  Misting 2 min 8.1 0.5 0.72 17.0 Site B  Control 3.2 0.2 0.82  Misting 4 min 7.5 0.2 0.57 28.9 Site C  Control 2.6 0.9 0.86  Misting 2 min 7.9 0.9 0.78 8.9 Test PM10 decay (h−1) Air exchange rate (h−1) NC [-] RRE of PM10 (%) Laboratory  Control 2.6 ± 0.7 0.3 ± 0.03 0.92 ± 0.02  Misting 2 min 10 ± 2.6 0.3 ± 0.05 0.65 ± 0.05 29.7  Misting 4 min 12 ± 0.6 0.4 ± 0.03 0.35 ± 0.02 61.8 Site A  Control 3.9 0.5 0.87  Misting 2 min 8.1 0.5 0.72 17.0 Site B  Control 3.2 0.2 0.82  Misting 4 min 7.5 0.2 0.57 28.9 Site C  Control 2.6 0.9 0.86  Misting 2 min 7.9 0.9 0.78 8.9 NC = normalized concentration [equation (2)]; - = unitless; RRE = relative dust removal efficiency. View Large PM10 decay rates were on average four to five times higher with the 2- and 4-min misting compared to control tests in the laboratory (Table 2), resulting in CADR of 0.06 ± 0.02 m3 s−1 and 0.07 ± 0.005 m3 s−1, respectively. CADR was 16 ± 4.8 and 19 ± 2.2 m3 of air per liter of water with the 2- and 4-min misting (Fig. 3A). Figure 3. View largeDownload slide Clean air delivery rate (CADR) of PM10 per amount of used water: (A) laboratory test (AM ± SD); (B) field experiments. Figure 3. View largeDownload slide Clean air delivery rate (CADR) of PM10 per amount of used water: (A) laboratory test (AM ± SD); (B) field experiments. In control tests, the inhalable dust decay rate was, on average, 5.7 ± 3.1 h−1, whereas after misting periods of 2 and 4 min, the decay rates were 13 ± 8.6 h−1 and 19 ± 21 h−1, respectively (Fig. 2B). The RRE of inhalable dust concentration was 28% with 2-min misting, whereas 4-min misting achieved RRE by 54% (Table 3). In the 4-min misting test, the first decay sample was, in reality, collected 2 min later than that in the control test (Fig. 2B). Thus, the dust reduction of 54% is somewhat overestimated. Table 3. Inhalable dust concentrations (AM ± SD) and dust reduction of misting in the laboratory tests. Laboratory test Concentration (mg m−3) RRE (%)b Reference Dust decaya 1–4 min 6–11 min 16–21 min 28–38 min Control 15.9 ± 7.6 10.4 ± 4.3 7.3 ± 4.1 6.0 ± 3.0 3.0 ± 1.9 Misting 2 min 15.2 ± 3.6 7.0 ± 4.2 5.0 ± 3.7 3.8 ± 3.4 2.4 ± 2.0 27.6 Misting 4 min 9.4 ± 2.5 2.7 ± 2.8 1.0 ± 0.9 1.3 ± 17 0.8 ± 0.6 53.8 Laboratory test Concentration (mg m−3) RRE (%)b Reference Dust decaya 1–4 min 6–11 min 16–21 min 28–38 min Control 15.9 ± 7.6 10.4 ± 4.3 7.3 ± 4.1 6.0 ± 3.0 3.0 ± 1.9 Misting 2 min 15.2 ± 3.6 7.0 ± 4.2 5.0 ± 3.7 3.8 ± 3.4 2.4 ± 2.0 27.6 Misting 4 min 9.4 ± 2.5 2.7 ± 2.8 1.0 ± 0.9 1.3 ± 17 0.8 ± 0.6 53.8 RRE = relative dust removal efficiency. aSampling time points presented from end of misting. bBased on normalized concentrations [data not shown, equation (2)] at time point 1–4 min after misting. View Large Table 3. Inhalable dust concentrations (AM ± SD) and dust reduction of misting in the laboratory tests. Laboratory test Concentration (mg m−3) RRE (%)b Reference Dust decaya 1–4 min 6–11 min 16–21 min 28–38 min Control 15.9 ± 7.6 10.4 ± 4.3 7.3 ± 4.1 6.0 ± 3.0 3.0 ± 1.9 Misting 2 min 15.2 ± 3.6 7.0 ± 4.2 5.0 ± 3.7 3.8 ± 3.4 2.4 ± 2.0 27.6 Misting 4 min 9.4 ± 2.5 2.7 ± 2.8 1.0 ± 0.9 1.3 ± 17 0.8 ± 0.6 53.8 Laboratory test Concentration (mg m−3) RRE (%)b Reference Dust decaya 1–4 min 6–11 min 16–21 min 28–38 min Control 15.9 ± 7.6 10.4 ± 4.3 7.3 ± 4.1 6.0 ± 3.0 3.0 ± 1.9 Misting 2 min 15.2 ± 3.6 7.0 ± 4.2 5.0 ± 3.7 3.8 ± 3.4 2.4 ± 2.0 27.6 Misting 4 min 9.4 ± 2.5 2.7 ± 2.8 1.0 ± 0.9 1.3 ± 17 0.8 ± 0.6 53.8 RRE = relative dust removal efficiency. aSampling time points presented from end of misting. bBased on normalized concentrations [data not shown, equation (2)] at time point 1–4 min after misting. View Large Dust reduction in the field In the field experiments, the normalized PM10 concentration reduced by 17% in site A, 29% in site B, and 9% in site C (Fig. 4A–C, Table 2). However, in site C, the scattering in the misting test decay line infers that the misting has acted as an air mover rather than actually removed the PM10 particles (Fig. 4C). The PM10 decay rate was similar, ~8 h−1 in all study sites, while the control decay rates varied between study sites (Table 2). CADRs were 0.03, 0.07, and 0.05 m3 s−1 in sites A–C, respectively. CADR varied between 11 and 17 m3 of air per liter of water (Fig. 4B). The highest CADR was obtained in site B, which had the greatest room volume (56 m3) compared to laboratory and other sites (27–36 m3). Figure 4. View largeDownload slide PM10 decays over time of control and misting tests in the field: (A) Site A; (B) Site B; (C) Site C. Figure 4. View largeDownload slide PM10 decays over time of control and misting tests in the field: (A) Site A; (B) Site B; (C) Site C. RRE of inhalable dust after an hour from the misting was 86–95% in sites A and B (Table 4). However, in site C, there was a substantially lower RRE of inhalable dust (3%). Table 4. Inhalable dust concentrations and dust reduction of misting in the field tests. Field test Concentration (mg m−3) RRE (%)b Reference Dust decaya Site A  Control 8.3 3.8 —  Misting 2 min 17 0.4 95.0 Site B  Control 18 11 —  Misting 4 min 38 3.2 85.8 Site C  Control 17 3.9 —  Misting 2 min 14 3.2 3.0 Field test Concentration (mg m−3) RRE (%)b Reference Dust decaya Site A  Control 8.3 3.8 —  Misting 2 min 17 0.4 95.0 Site B  Control 18 11 —  Misting 4 min 38 3.2 85.8 Site C  Control 17 3.9 —  Misting 2 min 14 3.2 3.0 RRE = relative dust removal efficiency. aDust decay over 60-min sampling period. bDecay based on normalized concentrations [equation (2)]. View Large Table 4. Inhalable dust concentrations and dust reduction of misting in the field tests. Field test Concentration (mg m−3) RRE (%)b Reference Dust decaya Site A  Control 8.3 3.8 —  Misting 2 min 17 0.4 95.0 Site B  Control 18 11 —  Misting 4 min 38 3.2 85.8 Site C  Control 17 3.9 —  Misting 2 min 14 3.2 3.0 Field test Concentration (mg m−3) RRE (%)b Reference Dust decaya Site A  Control 8.3 3.8 —  Misting 2 min 17 0.4 95.0 Site B  Control 18 11 —  Misting 4 min 38 3.2 85.8 Site C  Control 17 3.9 —  Misting 2 min 14 3.2 3.0 RRE = relative dust removal efficiency. aDust decay over 60-min sampling period. bDecay based on normalized concentrations [equation (2)]. View Large Discussion It is generally considered more effective to capture dust at source rather than from air. However, dust concentrations may not reduce below occupational exposure limit values despite the use of on-tool source controls that are used during tasks. Thus, it is reasonable to develop supplementary control techniques to use after tasks to improve the control of airborne dust. The study evaluated airborne dust removal by short-term water misting following the completion of dust-producing tasks. The results showed that the method substantially captured airborne dust during the misting period and for a short period after that. Despite this, there are some limitations in the feasibility of short-term misting, which are discussed later. Nevertheless, the performed short-term misting did not cause significant wetting of materials according to visual observations and RH measurements. Laboratory tests illustrated that the measured decrease in airborne PM10 dust was 30% in controlled laboratory conditions through avoiding water condensation on surfaces. In the field experiments, a slightly lower RRE of PM10 (9–29%) was achieved without wetting surfaces. Our results are lower than those observed by Organiscak and Leon (1994), who showed a respirable dust reduction of 70–90% with short-term water spraying used after dust generation. However, their findings are most likely overestimated because the results were not compared to a control decay without water spray, nor was the water amount reported. In addition, the different spray and misting systems and their characteristics most likely explain the less efficient dust removal in this study. Moreover, we measured PM10 particles, whereas they monitored the respirable fraction. Nevertheless, optically measured spray removal rates determined from instantaneous concentrations after a spray period resulted in a respirable dust decay rate of ~6–10 m3 min−1 (Organiscak and Leon, 1994). Our findings for the PM10 fraction in laboratory tests were similar: on average 4.5 ± 1.2 m3 min−1 with 2-min misting, and 5.6 ± 0.3 m3 min−1 with 4-min misting period. Our findings regarding the removal of airborne PM10 particles by water misting is not as efficient as capturing the particles at their source in real time by applying mist directly onto the material, as carried out in the study by Brouwer et al. (2004). They found a dust reduction of 73–85% during the cutting of concrete slabs and tiles with jackhammer (flow rates 0.17–0.19 l min−1, with hollow cone spray nozzles). However, this study showed a similar RRE of inhalable dust compared to removal efficiency of respirable dust found in the studies of Brouwer et al. (2004) and Beamer et al. (2005). They reported respirable dust removal of 63–86% (Brouwer et al., 2004; Beamer et al., 2005). Beamer et al. (2005) mounted the mist on a brick or saw blade with total water flow varying between 0.30–1.1 l min−1. The reason for a less effective dust capture from air than at source is that small airborne dust particles are able to escape from interactions with water droplets induced into air because they have low interceptional and inertia parameters (Charinpanitkul and Tanthapanichakoon, 2011). The removal of inhalable dust is likely to be more efficient than that of PM10 particles, as was seen in the field experiments. In the enclosed field cases A and B, the RRE of inhalable dust (an hour after misting) was substantially higher (86–95%) compared to PM10 results in the field. The reduction through ventilation alone was estimated to be 18–39% during the filter sampling period. Disparity between the PM10 and inhalable dust results can be explained by water droplets having been shown to achieve the highest removal for dust type, with higher fraction of larger than 7 µm particles (highest particle size 10 µm; Charinpanitkul and Tanthapanichakoon, 2011). If an aerosol distribution is such that most of the aerosol mass lies in the range of particles larger than 5 µm, then removal of dust particles by water droplets will be rapid (Seinfeld and Pandis, 1998). For very large particles (>20 µm), the collection efficiency of a water droplet approaches unity, whereas removal of particles 0.1–1 µm diameter, i.e. minimum collection efficiency regime, is expected to be relatively slow (Seinfeld and Pandis, 1998). Inhalable dust results obtained in the laboratory (28–54%) were notably lower than at the field. This difference is most likely explained by a measurement error related to short filter sampling times in the laboratory tests, and differences in the dust distributions between laboratory and field. The dispersion of a test dust during its generation may not be complete, especially in the case of hydrophilic materials. This may produce a particle size distribution that is larger than the size distribution of the original test particles (Hinds, 1999). Therefore, probable incomplete dispersion in the laboratory may have resulted in larger particles than those generated in the field tasks. Supplementary Figure 1 (available at Annals of Work Exposures and Health online) verifies that the mass fraction of smaller particles was less in the laboratory tests than at the field. Dust-capture effectiveness of the handheld misting device can also be discussed in terms of the CADR. The CADR of misting remains constant, but the reduction in airborne dust concentration depends on the volume of the room and air exchange rate. Therefore, for example, the CARD was notably higher in site B compared to that in site A (0.07 m3 s−1 versus 0.03 m3 s−1) with greater room volume (56 m3 versus 30 m3, respectively), although both the air exchange (0.2 versus 0.5 h−1) and difference between the misting and natural decay rates (4.3 versus 4.2 h−1) were similar. Overall, the absolute mean clean air delivery volumes varied between 4.1–6.7 m3 in 2-min misting tests and 16–18 m3 in 4-min misting tests. In terms of clean air provided to the room space, the effectiveness of the handheld misting device used in this study can, to an extent, be compared to portable air cleaners, which are used for control of contaminant exposure in residential settings. It is recognized however, that a misting device is used only a few minutes after dust generation, whereas residential air cleaners are operating continuously. Recent studies by Noh and Oh (2015), Peck et al. (2016), and Zuraimi et al. (2017) have tested typical filter-based air cleaners in controlled environment settings with room volumes (24–31 m3) similar to the present laboratory room volume (27 m3). Overall, the highest CADR obtained by the handheld misting device reached a similar level to the lowest CADR values of air cleaners reported by Noh and Oh (2015), Peck et al. (2016), and Zuraimi et al. (2017). They used test particles 0.03–5.0 µm diameter. This study indicates that the misting technique may not be suitable for renovation or construction sites, which have an effective air exchange rate (i.e. effective dilution). One study site had a poor RRE (3%) of inhalable dust, most likely explained by the fact that the test rooms were more like open spaces compared to other study sites. The test rooms had two open doorways to the adjacent rooms, which may have caused uncontrolled air currents, producing a more dilutive effect than in the enclosed rooms. The ventilation alone (with assumed perfect mixing) was calculated to reduce the normalized inhalable dust concentration by 59% during the filter-sampling period. It is speculated that the mist moved the air and airborne dust rather than capturing the dust, as Pollock and Organiscak (2007) noticed in their study. In addition, the mist may have been carried away via air currents. This possibility is supported by the findings of Swanson and Langefeld (2015) who observed a significant decrease in droplet concentration and increase in droplet size at the higher air speed of 3–6 m s−1 compared to lower ventilation with an air speed of 1 m s−1. Another practical limitation of the more effective use of the misting method in airborne dust clearance is the avoidance of harmful wetting of materials. This was demonstrated in the controlled environment with the longer misting time: higher dust reduction was achieved (PM10 62% versus 30%, inhalable fraction 54% versus 28%) but the dew point was reached and water condensation on surfaces occurred. On the other hand, in theory (see Mollier diagram), misting times could have been longer in the field experiments to avoid water condensation on surfaces: in site A and C ~1 min, and site B nearly 2 min longer. With the longer misting periods, a similar reduction in PM10 to those achieved in the laboratory would likely have been reached. Thus, it would be of important to optimize the misting time. Nevertheless, short-term misting resulted in substantially lower inhalable dust concentration (<1 mg m−3) compared to that without the misting (3 mg m−3), half an hour after misting in the laboratory. This benefit was also shown in the field: an hour after misting, a high reduction in inhalable dust concentrations assuming similar air exchanges (and air currents) between the control and misting test conditions (site A and B). In addition, the highest CADRs, varying from 0.06 ± 0.02 m3 s−1 to 0.07 ± 0.005 m3 s−1, were achieved in the enclosed laboratory and site B. In enclosed spaces, the mist does not transfer elsewhere. Our findings suggest that the misting technique is a suitable dust control measure to use in enclosed spaces without disturbing air currents. It is nonetheless acknowledged that in the sites studied, the air change rates were low and may not be typical for construction sites. Nevertheless, using the misting method does not replace the required air exchange achieved by the negative pressurization during renovation projects. In this situation, high air exchange rate itself causes dilution. Finally, some tasks have little information regarding the efficacy of the on-tool spraying systems (such as jackhammers; Beaudry et al., 2013), whereas some interior tasks are more susceptible to high water consumption when water spraying is conducted in real time. Thus, short-term misting after a task is a potential measure to control airborne dust. Moreover, care should be taken with water volume usage, not only due to the risks of moisture damage, but also because working on moist material has been associated with elevated dust exposure levels (Tjoe Nij et al., 2003). Table 5 summarizes task-based wet suppression efficacy to reduce respirable dust and respirable crystalline silica (RCS) concentrations in interior works. However, as many interior tasks produce large amounts of dust, information regarding both the exposure control methods and airborne dust control measures after tasks are still missing. The summary in Table 5 emphasizes future research needs to study task-specific misting applications and their dust removal efficacy. Particularly, information regarding RCS is missing in several of the high dust-producing tasks (Table 5). The evaluation of the task-specific efficiency of a short-term misting to control airborne respirable fraction should be carried out. Table 5. Summary of the task-specific respirable dust (Resp) and RCS concentrations performed indoors with using water suppression. Dust reduction efficiency (RE) by wet methods. Task Study site Water suppression system Associated time Water flow rate (l min−1) Water droplet size (µm) Dust particle size (µm) Resp concentration (mg m−3) Resp RE (%) RCS concentration (mg m−3) RCS RE (%) Reference Brick cutting Laboratory Water flow on tool and material Real time 3 N/A NM AM particle count 1.1 × 105 93a NM NM Beamer et al. (2005) Water spray on tool and material Real time 0.30.541.1 N/A NM AM particle count6.3 × 105 5.3 × 105 3.2 × 105 63a 67a 79a NM NM Concrete cutting Laboratory Water flow on tool Real time NM N/A NM 2.9–7.0 81–92 NM NM Tjoe Nij et al. (2003) Concrete dismantling On-site Water spray on tool Real time 0.17–0.19 N/A NM NM NM 0.02–0.4 64–86 Brouwer et al. (2004) Concrete grinding Laboratory Water flow on tool Real time 3 N/A NM AM 17 (7.8) 98 AM 1.4 (0.4) 98 Akbar-Khanzadeh et al. (2007) Laboratory Water flow on tool Real time NM N/A NM AM 2.7 (1.3) 93 AM 0.3 (0.2) 94 Akbar-Khanzadeh et al. (2010) On-site Portable short-term misting After work completed, 2-min misting 0.22 50–80 NM 0.4 (inhalable dust) 95 (inhalable dust)29 (PM10) NM NM Present study Concrete roofing tiles cutting Laboratory Water flow on tool Real time 0.13 N/A NM 0.4–0.6 98 NM NM Carlo et al. (2010) Drywall sanding On-site Wet sponge sander Real time N/A N/A N/A AM 1.85 (1.15) 60 NM NM Young-Corbett et al. (2009) Drywall sanding and concrete grinding On-site Portable short-term misting After work completed, 4-min misting 0.22 50–80 NM 3.2 (inhalable dust) 86 (inhalable dust)17 (PM10) NM NM Present study Stone cutting On-site Water flow on tool Real time 2 N/A NM 3.5–7.5 89–95 1.9–4.9 89–96 Cooper et al. (2015) On-site Water flow on tool and water curtain Real time 2.0 for blade, 8.0 for curtain N/A NM 1.8–6.0 95–97 0.2–0.7 98–>99 Test dust generation Laboratory Fixed hollow cone spray nozzle After dust generation, 3-min spraying NM NM MMD 5.4–6.1 6.7–17.4 70–90 NM NM Organiscak and Leon (1994) Test dust generation Laboratory Fixed hollow-cone, full cone, flat fan, and air-atomized spray nozzles After dust generation, spraying time not reported 1.8–3.2 50–300 100% <44 µm and 65% <10 µm NR 10–40 NM NM Pollock and Organiscak (2007) Test dust generation Laboratory Full cone spray nozzle Real time NM 30–320(mean 100) 2.0–10 (mean 5.0) NM 22–24c NM NM Charinpanitkul and Tanthapanichakoon (2011) 80–1000 (mean 360) NM 20–22c NM Test dust generation Laboratory wind tunnel ×3 hollow cone spray nozzles Real time 2.95/ nozzle NM 0.61.02.1 NM AM 21 (3.3)AM 60 (2.8)AM 90 (8.6) NM NM Tessum et al. (2014) Test dust generation Laboratory Portable short-term misting After dust generation, 2-min misting; after dust generation, 4-min misting 0.22 50–80 NM AM 7.0 (5.2) (inhalable dust)AM 2.7 (2.8) (inhalable dust) 28 (inhalable dust)30 (PM10)54 (inhalable dust)30 (PM10) NM NM Present study Task Study site Water suppression system Associated time Water flow rate (l min−1) Water droplet size (µm) Dust particle size (µm) Resp concentration (mg m−3) Resp RE (%) RCS concentration (mg m−3) RCS RE (%) Reference Brick cutting Laboratory Water flow on tool and material Real time 3 N/A NM AM particle count 1.1 × 105 93a NM NM Beamer et al. (2005) Water spray on tool and material Real time 0.30.541.1 N/A NM AM particle count6.3 × 105 5.3 × 105 3.2 × 105 63a 67a 79a NM NM Concrete cutting Laboratory Water flow on tool Real time NM N/A NM 2.9–7.0 81–92 NM NM Tjoe Nij et al. (2003) Concrete dismantling On-site Water spray on tool Real time 0.17–0.19 N/A NM NM NM 0.02–0.4 64–86 Brouwer et al. (2004) Concrete grinding Laboratory Water flow on tool Real time 3 N/A NM AM 17 (7.8) 98 AM 1.4 (0.4) 98 Akbar-Khanzadeh et al. (2007) Laboratory Water flow on tool Real time NM N/A NM AM 2.7 (1.3) 93 AM 0.3 (0.2) 94 Akbar-Khanzadeh et al. (2010) On-site Portable short-term misting After work completed, 2-min misting 0.22 50–80 NM 0.4 (inhalable dust) 95 (inhalable dust)29 (PM10) NM NM Present study Concrete roofing tiles cutting Laboratory Water flow on tool Real time 0.13 N/A NM 0.4–0.6 98 NM NM Carlo et al. (2010) Drywall sanding On-site Wet sponge sander Real time N/A N/A N/A AM 1.85 (1.15) 60 NM NM Young-Corbett et al. (2009) Drywall sanding and concrete grinding On-site Portable short-term misting After work completed, 4-min misting 0.22 50–80 NM 3.2 (inhalable dust) 86 (inhalable dust)17 (PM10) NM NM Present study Stone cutting On-site Water flow on tool Real time 2 N/A NM 3.5–7.5 89–95 1.9–4.9 89–96 Cooper et al. (2015) On-site Water flow on tool and water curtain Real time 2.0 for blade, 8.0 for curtain N/A NM 1.8–6.0 95–97 0.2–0.7 98–>99 Test dust generation Laboratory Fixed hollow cone spray nozzle After dust generation, 3-min spraying NM NM MMD 5.4–6.1 6.7–17.4 70–90 NM NM Organiscak and Leon (1994) Test dust generation Laboratory Fixed hollow-cone, full cone, flat fan, and air-atomized spray nozzles After dust generation, spraying time not reported 1.8–3.2 50–300 100% <44 µm and 65% <10 µm NR 10–40 NM NM Pollock and Organiscak (2007) Test dust generation Laboratory Full cone spray nozzle Real time NM 30–320(mean 100) 2.0–10 (mean 5.0) NM 22–24c NM NM Charinpanitkul and Tanthapanichakoon (2011) 80–1000 (mean 360) NM 20–22c NM Test dust generation Laboratory wind tunnel ×3 hollow cone spray nozzles Real time 2.95/ nozzle NM 0.61.02.1 NM AM 21 (3.3)AM 60 (2.8)AM 90 (8.6) NM NM Tessum et al. (2014) Test dust generation Laboratory Portable short-term misting After dust generation, 2-min misting; after dust generation, 4-min misting 0.22 50–80 NM AM 7.0 (5.2) (inhalable dust)AM 2.7 (2.8) (inhalable dust) 28 (inhalable dust)30 (PM10)54 (inhalable dust)30 (PM10) NM NM Present study MMD = mass median diameter; AM (SD) = arithmetic mean (standard deviation); N/A = not applicable; NM = not measured; NR = not reported. aBased on estimation of mass fraction. bRE of thoracic fraction 47%. cBased on real size distribution data and average size data. View Large Table 5. Summary of the task-specific respirable dust (Resp) and RCS concentrations performed indoors with using water suppression. Dust reduction efficiency (RE) by wet methods. Task Study site Water suppression system Associated time Water flow rate (l min−1) Water droplet size (µm) Dust particle size (µm) Resp concentration (mg m−3) Resp RE (%) RCS concentration (mg m−3) RCS RE (%) Reference Brick cutting Laboratory Water flow on tool and material Real time 3 N/A NM AM particle count 1.1 × 105 93a NM NM Beamer et al. (2005) Water spray on tool and material Real time 0.30.541.1 N/A NM AM particle count6.3 × 105 5.3 × 105 3.2 × 105 63a 67a 79a NM NM Concrete cutting Laboratory Water flow on tool Real time NM N/A NM 2.9–7.0 81–92 NM NM Tjoe Nij et al. (2003) Concrete dismantling On-site Water spray on tool Real time 0.17–0.19 N/A NM NM NM 0.02–0.4 64–86 Brouwer et al. (2004) Concrete grinding Laboratory Water flow on tool Real time 3 N/A NM AM 17 (7.8) 98 AM 1.4 (0.4) 98 Akbar-Khanzadeh et al. (2007) Laboratory Water flow on tool Real time NM N/A NM AM 2.7 (1.3) 93 AM 0.3 (0.2) 94 Akbar-Khanzadeh et al. (2010) On-site Portable short-term misting After work completed, 2-min misting 0.22 50–80 NM 0.4 (inhalable dust) 95 (inhalable dust)29 (PM10) NM NM Present study Concrete roofing tiles cutting Laboratory Water flow on tool Real time 0.13 N/A NM 0.4–0.6 98 NM NM Carlo et al. (2010) Drywall sanding On-site Wet sponge sander Real time N/A N/A N/A AM 1.85 (1.15) 60 NM NM Young-Corbett et al. (2009) Drywall sanding and concrete grinding On-site Portable short-term misting After work completed, 4-min misting 0.22 50–80 NM 3.2 (inhalable dust) 86 (inhalable dust)17 (PM10) NM NM Present study Stone cutting On-site Water flow on tool Real time 2 N/A NM 3.5–7.5 89–95 1.9–4.9 89–96 Cooper et al. (2015) On-site Water flow on tool and water curtain Real time 2.0 for blade, 8.0 for curtain N/A NM 1.8–6.0 95–97 0.2–0.7 98–>99 Test dust generation Laboratory Fixed hollow cone spray nozzle After dust generation, 3-min spraying NM NM MMD 5.4–6.1 6.7–17.4 70–90 NM NM Organiscak and Leon (1994) Test dust generation Laboratory Fixed hollow-cone, full cone, flat fan, and air-atomized spray nozzles After dust generation, spraying time not reported 1.8–3.2 50–300 100% <44 µm and 65% <10 µm NR 10–40 NM NM Pollock and Organiscak (2007) Test dust generation Laboratory Full cone spray nozzle Real time NM 30–320(mean 100) 2.0–10 (mean 5.0) NM 22–24c NM NM Charinpanitkul and Tanthapanichakoon (2011) 80–1000 (mean 360) NM 20–22c NM Test dust generation Laboratory wind tunnel ×3 hollow cone spray nozzles Real time 2.95/ nozzle NM 0.61.02.1 NM AM 21 (3.3)AM 60 (2.8)AM 90 (8.6) NM NM Tessum et al. (2014) Test dust generation Laboratory Portable short-term misting After dust generation, 2-min misting; after dust generation, 4-min misting 0.22 50–80 NM AM 7.0 (5.2) (inhalable dust)AM 2.7 (2.8) (inhalable dust) 28 (inhalable dust)30 (PM10)54 (inhalable dust)30 (PM10) NM NM Present study Task Study site Water suppression system Associated time Water flow rate (l min−1) Water droplet size (µm) Dust particle size (µm) Resp concentration (mg m−3) Resp RE (%) RCS concentration (mg m−3) RCS RE (%) Reference Brick cutting Laboratory Water flow on tool and material Real time 3 N/A NM AM particle count 1.1 × 105 93a NM NM Beamer et al. (2005) Water spray on tool and material Real time 0.30.541.1 N/A NM AM particle count6.3 × 105 5.3 × 105 3.2 × 105 63a 67a 79a NM NM Concrete cutting Laboratory Water flow on tool Real time NM N/A NM 2.9–7.0 81–92 NM NM Tjoe Nij et al. (2003) Concrete dismantling On-site Water spray on tool Real time 0.17–0.19 N/A NM NM NM 0.02–0.4 64–86 Brouwer et al. (2004) Concrete grinding Laboratory Water flow on tool Real time 3 N/A NM AM 17 (7.8) 98 AM 1.4 (0.4) 98 Akbar-Khanzadeh et al. (2007) Laboratory Water flow on tool Real time NM N/A NM AM 2.7 (1.3) 93 AM 0.3 (0.2) 94 Akbar-Khanzadeh et al. (2010) On-site Portable short-term misting After work completed, 2-min misting 0.22 50–80 NM 0.4 (inhalable dust) 95 (inhalable dust)29 (PM10) NM NM Present study Concrete roofing tiles cutting Laboratory Water flow on tool Real time 0.13 N/A NM 0.4–0.6 98 NM NM Carlo et al. (2010) Drywall sanding On-site Wet sponge sander Real time N/A N/A N/A AM 1.85 (1.15) 60 NM NM Young-Corbett et al. (2009) Drywall sanding and concrete grinding On-site Portable short-term misting After work completed, 4-min misting 0.22 50–80 NM 3.2 (inhalable dust) 86 (inhalable dust)17 (PM10) NM NM Present study Stone cutting On-site Water flow on tool Real time 2 N/A NM 3.5–7.5 89–95 1.9–4.9 89–96 Cooper et al. (2015) On-site Water flow on tool and water curtain Real time 2.0 for blade, 8.0 for curtain N/A NM 1.8–6.0 95–97 0.2–0.7 98–>99 Test dust generation Laboratory Fixed hollow cone spray nozzle After dust generation, 3-min spraying NM NM MMD 5.4–6.1 6.7–17.4 70–90 NM NM Organiscak and Leon (1994) Test dust generation Laboratory Fixed hollow-cone, full cone, flat fan, and air-atomized spray nozzles After dust generation, spraying time not reported 1.8–3.2 50–300 100% <44 µm and 65% <10 µm NR 10–40 NM NM Pollock and Organiscak (2007) Test dust generation Laboratory Full cone spray nozzle Real time NM 30–320(mean 100) 2.0–10 (mean 5.0) NM 22–24c NM NM Charinpanitkul and Tanthapanichakoon (2011) 80–1000 (mean 360) NM 20–22c NM Test dust generation Laboratory wind tunnel ×3 hollow cone spray nozzles Real time 2.95/ nozzle NM 0.61.02.1 NM AM 21 (3.3)AM 60 (2.8)AM 90 (8.6) NM NM Tessum et al. (2014) Test dust generation Laboratory Portable short-term misting After dust generation, 2-min misting; after dust generation, 4-min misting 0.22 50–80 NM AM 7.0 (5.2) (inhalable dust)AM 2.7 (2.8) (inhalable dust) 28 (inhalable dust)30 (PM10)54 (inhalable dust)30 (PM10) NM NM Present study MMD = mass median diameter; AM (SD) = arithmetic mean (standard deviation); N/A = not applicable; NM = not measured; NR = not reported. aBased on estimation of mass fraction. bRE of thoracic fraction 47%. cBased on real size distribution data and average size data. View Large Conclusions The study indicated that short-term water misting after a dust-producing task is an effective measure to control the dispersal of airborne dust. The method is an appropriate one to supplement on-tool source control measures, because misting substantially captures the airborne dust that has not been captured in real time by source controls. Short-term misting is, however, feasible in those indoor environments where effective air exchange is not possible to arrange. The performed short-term misting did not soak the materials; therefore, it is a safer technique for materials relative to running water applications. The short misting periods applied in this study may be considered as a ‘safety margin’ to avoid moisture damage to materials. To further develop the method, in addition to assessing visible condensation, the moisture content of materials should be assessed in order to maximize the airborne dust removal by the misting technique. The knowledge gained from this experimental study and previous theoretical studies of the spray characteristics provide a basis to develop more effective handheld misting techniques. Finally, as in the case of all wet methods, surface cleaning (e.g. vacuuming) after short-term misting is required to prevent the once settled dust being released in the air again and redispersed. Funding The Finnish Work Environment Fund (112249) funded the work described in this article. Acknowledgement The authors thank Joanne Enstone, MPhil, for linguistic editing of this article. The authors declare no conflict of interest relating to the material presented in this article. Its contents, including any opinions and/or conclusions expressed, are solely those of the authors. References Akbar-Khanzadeh F , Milz S , Ames A et al. (2007) Crystalline silica dust and respirable particulate matter during indoor concrete grinding - wet grinding and ventilated grinding compared with uncontrolled conventional grinding . J Occup Environ Hyg ; 4 : 770 – 9 . Google Scholar Crossref Search ADS PubMed Akbar-Khanzadeh F , Milz SA , Wagner CD et al. (2010) Effectiveness of dust control methods for crystalline silica and respirable suspended particulate matter exposure during manual concrete surface grinding . J Occup Environ Hyg ; 7 : 700 – 11 . Google Scholar Crossref Search ADS PubMed Beamer BR , Shulman S , Maynard A et al. (2005) Evaluation of misting controls to reduce respirable silica exposure for brick cutting . Ann Occup Hyg ; 49 : 503 – 10 . Google Scholar PubMed Beaudry C , Dion C , Gérin M et al. (2013) Construction workers’ exposure to crystalline silica literature review and analysis. Report R-771 . ISBN: 978-2-89631-659-5 (PDF). Montréal, Québec, Canada : Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST). pp. 1 – 108 . Available at http://www.irsst.qc.ca/media/documents/PubIRSST/R-771.pdf?v=2018-11-15. Accessed 15 November 2018. Brouwer D , Spee T , Huijbers R et al. (2004) Effectiveness of dust control by atomization of water sprays on handheld demolition and soil compacting equipment . TtA ; 4 : 68 ‒ 74 . Carlo RV , Sheehy J , Feng HA et al. (2010) Laboratory evaluation to reduce respirable crystalline silica dust when cutting concrete roofing tiles using a masonry saw . J Occup Environ Hyg ; 7 : 245 – 51 . Google Scholar Crossref Search ADS PubMed Charinpanitkul T , Tanthapanichakoon W (2011) Deterministic model of open-space dust removal system using water spray nozzle: effects of polydispersity of water droplet and dust particle . Sep Purif Technol ; 77 : 382 ‒ 8 . Google Scholar Crossref Search ADS Cooper JH , Johnson DL , Phillips ML (2015) Respirable silica dust suppression during artificial stone countertop cutting . Ann Occup Hyg ; 59 : 122 – 6 . Google Scholar PubMed Croteau G , Flanagan M , Camp J et al. (2004) The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding . Ann Occup Hyg ; 48 : 509 ‒ 18 . Google Scholar PubMed Flanagan ME , Seixas N , Becker P et al. (2006) Silica exposure on construction sites: results of an exposure monitoring data compilation project . J Occup Environ Hyg ; 3 : 144 – 52 . Google Scholar Crossref Search ADS PubMed Hak-Joon K , Bangwoo H , Yong-Jin K et al. (2012) Efficient test method for evaluating gas removal performance of room air cleaners using FTIR measurement and CADR calculation . Build Environ ; 47 : 385 ‒ 93 . Google Scholar Crossref Search ADS Health and Safety Executive (HSE) . (2017) Controlling airborne contaminants at work. A guide to local exhaust ventilation (LEV). HSG258. TSO part of Williams Lea Tag. Available at http://www.hse.gov.uk/pUbns/priced/hsg258.pdf. Accessed 3 October 2018. Helsel D (2005) Nondetects and data analysis: statistics for censored environmental data. In Scott M , Barnett V , editors. Hoboken, NJ : Wiley Interscience . pp. 1 – 250 . Hinds W (1999) Aerosol technology. Properties, behavior, and measurement of airborne particles . 2 nd edn. John Wiley & Sons, Inc. , Hoboken, NJ . McCoy JF , Schroeder WE , Rajan SR et al. (1985) New laboratory measurement method for water spray dust control effectiveness . Am Ind Hyg Assoc J ; 46 : 735 ‒ 40 . Google Scholar Crossref Search ADS Meeker JD , Cooper MR , Lefkowitz D et al. (2009) Engineering control technologies to reduce occupational silica exposures in masonry cutting and tuckpointing . Public Health Rep ; 124 ( Suppl. 1 ): 101 – 11 . Google Scholar Crossref Search ADS PubMed Noh KC , Oh MD (2015) Variation of clean air delivery rate and effective air cleaning ratio of room air cleaning devices . Build Environ ; 84 : 44 ‒ 9 . Google Scholar Crossref Search ADS Organiscak J , Leon M (1994) Influence of coal type on water spray suppression of airborne respirable dust . Aerosol Sci Technol ; 21 : 110 ‒ 8 . Google Scholar Crossref Search ADS Peck RL , Grinshpun SA , Yermakov M et al. (2016) Efficiency of portable HEPA air purifiers against traffic related combustion particles . Build Environ ; 98 : 21 ‒ 9 . Google Scholar Crossref Search ADS Pollock D , Organiscak J (2007) Airborne dust capture and induced airflow of various spray nozzle designs . Aerosol Sci Technol ; 41 : 711 ‒ 20 . Google Scholar Crossref Search ADS Sauvé JF , Beaudry C , Bégin D et al. (2013) Silica exposure during construction activities: statistical modeling of task-based measurements from the literature . Ann Occup Hyg ; 57 : 432 – 43 . Google Scholar PubMed Seinfeld J , Pandis S (1998) Atmospheric chemistry and physics. From air pollution to climate change . New York : John Wiley & Sons, Inc . Shepherd S , Woskie S , Holcroft C , Ellenbecker M (2009) Reducing quartz and dust exposures in construction during use of powered concrete-cutting hand tools: efficacy of local exhaust ventilation on hammer drills . JOEH ; 6 : 42 ‒ 51 . Google Scholar PubMed Swanson JG , Langefeld O (2015) Fundamental research in water spray systems for dust control . Min Tech ; 124 : 78 ‒ 82 . Google Scholar Crossref Search ADS Tessum MW , Raynor PC , Keating-Klika L (2014) Factors influencing the airborne capture of respirable charged particles by surfactants in water sprays . J Occup Environ Hyg ; 11 : 571 – 82 . Google Scholar Crossref Search ADS PubMed Tjoe Nij E , Hilhorst S , Spee T et al. (2003) Dust control measures in the construction industry . Ann Occup Hyg ; 47 : 211 – 8 . Google Scholar PubMed Tjoe Nij E , Höhr D , Borm P et al. (2004) Variability in quartz exposure in the construction industry: implications for assessing exposure-response relations . J Occup Environ Hyg ; 1 : 191 – 8 . Google Scholar Crossref Search ADS PubMed World Health Organization (WHO) . (1999) Hazard prevention and control in the work environment: airborne dust . Geneva : WHO/SDE/OEH/99.14 . Young-Corbett DE , Nussbaum MA (2009) Dust control effectiveness of drywall sanding tools . J Occup Environ Hyg ; 6 : 385 – 9 . Google Scholar Crossref Search ADS PubMed Zuraimi MS , Vuotari M , Nilsson G et al. (2017) Impact of dust loading on long term portable air cleaner performance . Build Environ ; 112 : 261 ‒ 9 . Google Scholar Crossref Search ADS © The Author(s) 2018. Published by Oxford University Press on behalf of the British Occupational Hygiene Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
TI - The Evaluation of Short-Term Water Misting of Room Air in Reducing Airborne Dust after Renovation Work
JF - Annals of Work Exposures and Health (formerly Annals Of Occupational Hygiene)
DO - 10.1093/annweh/wxy096
DA - 2019-02-16
UR - https://www.deepdyve.com/lp/oxford-university-press/the-evaluation-of-short-term-water-misting-of-room-air-in-reducing-VCQ6lfRt9c
SP - 242
VL - 63
IS - 2
DP - DeepDyve
ER -