Annals of Occupational Hygiene - Advance Access

Airborne Nanoparticle Exposures while Using Constant-Flow, Constant-Velocity, and Air-Curtain-Isolated Fume Hoods

Tsai, S.-J., Huang, R. F., Ellenbecker, M. J. — Fri, 20 Nov 2009 05:19:32 PST

Tsai et al. (Airborne nanoparticle exposures associated with the manual handling of nanoalumina and nanosilver in fume hoods. J Nanopart Res 2009; 11: 147–61) found that the handling of dry nanoalumina and nanosilver inside laboratory fume hoods can cause a significant release of airborne nanoparticles from the hood. Hood design affects the magnitude of release. With traditionally designed fume hoods, the airflow moves horizontally toward the hood cupboard; the turbulent airflow formed in the worker wake region interacts with the vortex in the constant-flow fume hood and this can cause nanoparticles to be carried out with the circulating airflow. Airborne particle concentrations were measured for three hood designs (constant-flow, constant-velocity, and air-curtain hoods) using manual handling of nanoalumina particles. The hood operator's airborne nanoparticle breathing zone exposure was measured over the size range from 5 nm to 20 µm. Experiments showed that the exposure magnitude for a constant-flow hood had high variability. The results for the constant-velocity hood varied by operating conditions, but were usually very low. The performance of the air-curtain hood, a new design with significantly different airflow pattern from traditional hoods, was consistent under all operating conditions and release was barely detected. Fog tests showed more intense turbulent airflow in traditional hoods and that the downward airflow from the double-layered sash to the suction slot of the air-curtain hood did not cause turbulence seen in other hoods.

Evaluation of an Electrically Heated Vest (EHV) Using a Thermal Manikin in Cold Environments

Wang, F., Lee, H. — Mon, 09 Nov 2009 03:57:25 PST

We studied the heating efficiency of an electrically heated vest (EHV), its relationship to the microclimate temperature distribution in a three-layer clothing ensemble, and the effect of an EHV on the clothing's total thermal insulation by both theoretical analysis and thermal manikin measurements. The heat losses at different ambient conditions and heating states were recorded and the heating efficiency of the EHV was calculated. It was found that the EHV can alter the microclimatic temperature distribution of the three-layer clothing ensemble. The EHV can provide an air temperature of 34°C around the manikin's torso skin. The highest temperature on the outside surface of the EHV was around 38°C, which indicates that it is safe for the consumer. The higher the heating temperature, the lower the heating efficiency obtained. This was due to much more heat being lost to the environment, and hence, the heat gain from the EHV was smaller. The heating efficiency decreased from 55.3% at 0°C to 27.4% at –10°C when the heating power was set at 13 W. We suggest adjusting the heating power to 5 W (step 1) at an ambient temperature of 0°C, while at –10°C using 13 W (step 3) to provide the consumer a thermal comfort condition.

Comparison of Direct and Indirect Methods of Measuring Airborne Chrysotile Fibre Concentration

Eypert-Blaison, C., Veissiere, S., Rastoix, O., Kauffer, E. — Wed, 07 Oct 2009 07:38:15 PDT

Transmission electron microscopy observations most frequently form a basis for estimating asbestos fibre concentration in the environment and in buildings with asbestos-containing materials. Sampled fibres can be transferred to microscope grids by applying either a direct [ISO (1995) Draft International ISO/DIS 10312. Ambient air. Determination of asbestos fibres. Direct transfer transmission electron microscopy procedure. Geneva, Switzerland: International Standardization Organization] or an indirect [AFNOR (1996) Détermination de la concentration en fibres d'amiante par microscopie électronique à transmission—Méthode indirecte. Cedex, France: AFNOR, p. 42; ISO (1997) Draft International ISO/DIS 13794. Ambient air. Determination of asbestos fibres. Indirect-transfer transmission electron microscopy procedure. Geneva, Switzerland: International Standardization Organization] method. In the latter case, ISO Standard 13794 recommends filtering calcination residues either on a polycarbonate (PC) filter (PC indirect method) or on a cellulose ester (CE) membrane (CE indirect method). The PC indirect method requires that fibres deposited on a PC filter be covered by a carbon layer, whereas in the CE indirect method, the CE membrane has to be directly processed using a method described in ISO Standard 10312. The purpose of this study was to compare results obtained using, on the one hand, direct preparation methods and, on the other hand, PC indirect or CE indirect methods, for counting asbestos fibres deposited on filters as a result of liquid filtration or air sampling. In direct method-based preparation, we observed that an etching time of 6–14 min does not affect the measured densities, except for fibres <1 µm deposited by liquid filtration. Moreover, in all cases, the direct method gives higher densities than the PC indirect method because of possible fibre disappearance when using the carbon evaporator implemented in the PC indirect method. The CE membrane used for sample preparation in the CE indirect method is collapsed prior to passing it through the carbon evaporator, so the fibres are less likely to disappear at this stage. We then note that the resulting fibre densities for chrysotile-loaded filters prepared using the direct method are close to those obtained with filters prepared using the CE indirect method. Our study therefore shows that, under the implemented experimental conditions, the PC and CE indirect preparation methods described in ISO Standard 13794 are not equivalent.

Quantitative Plasma Biomarker Analysis in HDI Exposure Assessment

Sun, 04 Oct 2009 19:24:30 PDT

Quantification of amines in biological samples is important for evaluating occupational exposure to diisocyanates. In this study, we describe the quantification of 1,6-hexamethylene diamine (HDA) levels in hydrolyzed plasma of 46 spray painters applying 1,6-hexamethylene diisocyanate (HDI)-containing paint in vehicle repair shops collected during repeated visits to their workplace and their relationship with dermal and inhalation exposure to HDI monomer. HDA was detected in 76% of plasma samples, as heptafluorobutyryl derivatives, and the range of HDA concentrations was ≤0.02–0.92 µg l^–1. After log-transformation of the data, the correlation between plasma HDA levels and HDI inhalation exposure measured on the same workday was low (N = 108, r = 0.22, P = 0.026) compared with the correlation between plasma HDA levels and inhalation exposure occurring ~20 to 60 days before blood collection (N = 29, r = 0.57, P = 0.0014). The correlation between plasma HDA levels and HDI dermal exposure measured on the same workday, although statistically significant, was low (N = 108, r = 0.22, P = 0.040) while the correlation between HDA and dermal exposure occurring ~20 to 60 days before blood collection was slightly improved (N = 29, r = 0.36, P = 0.053). We evaluated various workplace factors and controls (i.e. location, personal protective equipment use and paint booth type) as modifiers of plasma HDA levels. Workers using a downdraft-ventilated booth had significantly lower plasma HDA levels relative to semi-downdraft and crossdraft booth types (P = 0.0108); this trend was comparable to HDI inhalation and dermal exposure levels stratified by booth type. These findings indicate that HDA concentration in hydrolyzed plasma may be used as a biomarker of cumulative inhalation and dermal exposure to HDI and for investigating the effectiveness of exposure controls in the workplace.

Dermal and Inhalation Exposure to Methylene Bisphenyl Isocyanate (MDI) in Iron Foundry Workers

Sat, 26 Sep 2009 00:04:06 PDT

Diisocyanates are a group of chemically reactive agents, which are used in the production of coatings, adhesives, polyurethane foams, and parts for the automotive industry and as curing agents for cores in the foundry industry. Dermal and inhalation exposure to methylene bisphenyl isocyanate (MDI) is associated with respiratory sensitization and occupational asthma. However, limited research has been performed on the quantitative evaluation of dermal and inhalation exposure to MDI in occupationally exposed workers. The objective of this research was to quantify dermal and inhalation exposure levels in iron foundry workers. Workers involved in mechanized moulding and mechanized production of cores were monitored: 12 core makers, 2 core-sand preparers, and 5 core installers. Personal breathing-zone levels of MDI were measured using impregnated filter sampling. Dermal exposure to MDI was measured using a tape-strip technique. Three or five consecutive tape-strip samples were collected from five exposed skin areas (right and left forefingers, left and right wrists, and forehead). The average personal air concentration was 0.55 µg m^–3, 50-fold lower than the Swedish occupational exposure limit of 30 µg m^–3. The core makers had an average exposure of 0.77 µg m^–3, which was not significantly different from core installers’ and core-sand preparers’ average exposure of 0.16 µg m^–3 (P = 0.059). Three core makers had a 10-fold higher inhalation exposure than the other core makers. The core makers’ mean dermal exposure at different skin sites varied from 0.13 to 0.34 µg while the two other groups’ exposure ranged from 0.006 to 0.062 µg. No significant difference was observed in the MDI levels between the skin sites in a pairwise comparison, except for left forefinger compared to left and right wrist (P < 0.05). In addition, quantifiable but decreasing levels of MDI were observed in the consecutive tape strip per site indicating MDI penetration into the skin. This study indicates that exposure to MDI can be quantified on workers’ skin even if air levels are close to unquantifiable. Thus, the potential for uncured MDI to deposit on and penetrate into the skin is demonstrated. Therefore, dermal exposure along with inhalation exposure to MDI should be measured in the occupational settings where MDI is present in order to shed light on their roles in the development of occupational isocyanate asthma.

Characterization and Assessment of Dermal and Inhalable Nickel Exposures in Nickel Production and Primary User Industries

Hughson, G. W., Galea, K. S., Heim, K. E. — Wed, 16 Sep 2009 07:05:53 PDT

The aim of this study was to measure the levels of nickel in the skin contaminant layer of workers involved in specific processes and tasks within the primary nickel production and primary nickel user industries. Dermal exposure samples were collected using moist wipes to recover surface contamination from defined areas of skin. These were analysed for soluble and insoluble nickel species. Personal samples of inhalable dust were also collected to determine the corresponding inhalable nickel exposures. The air samples were analysed for total inhalable dust and then for soluble, sulfidic, metallic, and oxidic nickel species. The workplace surveys were carried out in five different workplaces, including three nickel refineries, a stainless steel plant, and a powder metallurgy plant, all of which were located in Europe. Nickel refinery workers involved with electrolytic nickel recovery processes had soluble dermal nickel exposure of 0.34 µg cm^–2 [geometric mean (GM)] to the hands and forearms. The GM of soluble dermal nickel exposure for workers involved in packing nickel salts (nickel chloride hexahydrate, nickel sulphate hexahydrate, and nickel hydroxycarbonate) was 0.61 µg cm^–2. Refinery workers involved in packing nickel metal powders and end-user powder operatives in magnet production had the highest dermal exposure (GM = 2.59 µg cm^–2 soluble nickel). The hands, forearms, face, and neck of these workers all received greater dermal nickel exposure compared with the other jobs included in this study. The soluble nickel dermal exposures for stainless steel production workers were at or slightly above the limit of detection (0.02 µg cm^–2 soluble nickel). The highest inhalable nickel concentrations were observed for the workers involved in nickel powder packing (GM = 0.77 mg m^–3), although the soluble component comprised only 2% of the total nickel content. The highest airborne soluble nickel exposures were associated with refineries using electrolytic processes for nickel recovery (GM = 0.04 mg m^–3 total nickel, containing 82% soluble nickel) and those jobs involving contact with soluble nickel compounds (GM = 0.02 mg m^–3 total nickel content, containing 76% soluble nickel). The stainless steel workers were exposed to low concentrations of relatively insoluble airborne nickel species (GM = 0.03 mg m^–3 total nickel, containing 1% soluble nickel). A statistically significant correlation was observed between dermal exposures for all anatomical areas across all tasks. In addition, the dermal and inhalable (total) nickel exposures were similarly associated. Overall, dermal exposures to nickel, nickel compounds, and nickel alloys were relatively low. However, exposures were highly variable, which can be explained by the inconsistent use of personal protective equipment, varying working practices, and different standards of automation and engineering controls within each exposure category.

Large Particle Penetration through N95 Respirator Filters and Facepiece Leaks with Cyclic Flow

Fri, 21 Aug 2009 05:21:27 PDT

The aim of this study was to investigate respirator filter and faceseal penetration of particles representing bacterial and fungal spore size ranges (0.7–4 µm). First, field experiments were conducted to determine workplace protection factors (WPFs) for a typical N95 filtering facepiece respirator (FFR). These data (average WPF = 515) were then used to position the FFR on a manikin to simulate realistic donning conditions for laboratory experiments. Filter penetration was also measured after the FFR was fully sealed on the manikin face. This value was deducted from the total penetration (obtained from tests with the partially sealed FFR) to determine the faceseal penetration. All manikin experiments were repeated using three sinusoidal breathing flow patterns corresponding to mean inspiratory flow rates of 15, 30, and 85 l min^–1. The faceseal penetration varied from 0.1 to 1.1% and decreased with increasing particle size (P < 0.001) and breathing rate (P < 0.001). The fractions of aerosols penetrating through the faceseal leakage varied from 0.66 to 0.94. In conclusion, even for a well-fitting FFR respirator, most particle penetration occurs through faceseal leakage, which varies with breathing flow rate and particle size.

CFD Simulation of Contaminant Decay for High Reynolds Flow in a Controlled Environment

Lambert, A. R., Lin, C.-L., Mardorf, E., O'shaughnessy, P. — Tue, 11 Aug 2009 09:29:25 PDT

This study examines the usage of computational fluid dynamics (CFDs) for estimating the time-elapsed decay of contaminants within a chamber experiencing high Reynolds flow. CFD results were compared with measurements taken at a controlled facility. In addition, parameters of the CFD simulation were examined; namely the effects of turbulence and inertial transport at high Reynolds number ventilating flows, as well as inlet duct configuration and its effect on the inlet velocity profile. The agreement between the computational and experimental clearance times was quite good, with percent errors as low as –5.32% at high flow rate and –11.8% at the lower flow rate. This study determined that for high Reynolds flow, diffusive transport effects may be ignored as the majority of mass is transported via the bulk stream, i.e. momentum transport. In addition, resolving the inlet velocity profile was of prime importance for accurate simulation of ventilating flows and prediction of contaminant washout. This was done by including the inlet duct geometry in the computational domain. In addition, it was found that despite different flow rates, the predicted contaminant washout took ~12–13% longer than predicted assuming instantaneous mixing. Furthermore, percent error between computational and experimental data as low as –5.32% shows that CFD is a useful tool for studying ventilation phenomena.

Determinants of Use of Hearing Protection Devices in Canadian Lumber Mill Workers

Sbihi, H., Teschke, K., Macnab, Y. C., Davies, H. W. — Wed, 01 Jul 2009 08:27:30 PDT

Background: In a cohort study of lumber mill workers’ exposure to noise and incidence of heart disease, initial noise estimates were likely overestimated because they did not account for reductions afforded by the use of hearing protection. As such information was seldom available for individual workers, modeling was necessary to predict hearing protection use and derive adjusted noise measures.

Objective: To develop a multilevel model of the likelihood of use of hearing protection devices (HPDs) for British Columbia (Canada) lumber mill workers.

Method: The study population included 13 147 workers in 14 sawmills for whom we had information on HPD use. Subjects self-reported their use of hearing protectors during routine hearing tests over their work history period. Separate multilevel logistic regression models with increasing complexity were developed for a subcohort of workers with complete information (n = 1493) and for a subcohort comprised subjects with hearing tests coinciding with their jobs (n = 10 203). The models included random intercepts for worker and for sawmill.

Results: HPD use was associated in both subcohorts with factors such as noise exposure and age. We also showed that specific jobs (such as sawfiling) and departments (planer, in particular) were strongly associated with the use of HPDs. The model illustrates the quantitative importance of including a hierarchical structure which allows for explaining potential sources of outcome variability.

Conclusions: We developed a hierarchical model to predict hearing protection use to enable correction of exposure assessments for use in retrospective epidemiological studies. We showed that this was feasible even in the absence of complete determinant information.