Human Exposure Chamber Research Articles

112 Comparing Various Size Fractions Collected Using Dusttrak And Gravimetric Samples

Abstract Occupational exposure concentrations are routinely collected using gravimetric samples. However, gravimetric samples typically require a long sampling time, especially when there are low exposure concentrations. While long sampling time may be appropriate to verify compliance with 8-h occupational limit values (OELs), they cannot address exposure's temporal and spatial heterogeneity or provide information on peak exposures present in the work environment. Real-time light scattering sensors enable the possibility of collecting high-resolution, low-cost measurements, quickly identifying peak and short-term concentrations, linking exposure to emission sources, and better understanding within-day variation. These technologies have become increasingly popular also for occupational monitoring purposes. In this presentation, the results of the dust samples collected for a randomized double-blinded controlled human exposure chamber study are presented. In six groups, 24 healthy volunteers were exposed to two common stone minerals, quartz diorite, and rhomb porphyry, in 4-h exposure sessions. To control the exposure in the chamber, personal gravimetric samples of respirable dust and stationary gravimetric samples of total dust, PM2.5, and respiratory dust were collected. Additionally, stationary real-time samples of total dust, respirable dust, PM10, PM2.5, and PM1 were collected continuously using DustTrak TSI model DRX 8533. Despite the many advantages of the real-time sensors, evaluating compliance with OELs should be done with caution. Except for the PM2.5 fraction, a significant difference was observed between the gravimetric and the DustTrak samples. While the DustTrak overestimated the PM2.5 concentrations, the total dust concatenations were underestimated by a factor of almost two compared to the gravimetric samples.

Association between exposure to different stone aggregates from asphalt and blood coagulability: A human exposure chamber study.

A large fraction of particulate matter (PM), especially PM10, concentrations are due to non-exhaust emissions, such as road abrasion and wear on tires and brake pads. Concentrating on road abrasion, we aimed to investigate blood coagulability in healthy adults after exposure to two types of stone materials commonly used in asphalt on Norwegian roads. This study followed a randomized, double-blind, cross-over study design. Using an exposure chamber, 24 healthy young volunteers were exposed to aggregates of two different types of rocks and placebo dust: quartz diorite, rhomb porphyry, and lactose (placebo dust). Each exposure session lasted for 4 hours (h), and blood samples were collected before exposure (baseline), 4h post-exposure, and 24h post-exposure to analyse potential changes in the von Willebrand factor (vWF) as well as of fibrinogen, d-dimer, leukocytes, and thrombocytes. The dust concentration in the exposure chamber was measured with real-time instruments and gravimetric samples of total dust, respirable dust, PM10, PM2.5, and ultrafine particles (UFP). The results were analysed using a linear mixed-effect model. Leukocyte blood counts increased post-exposure for all exposure materials; however, none of the increases were statistically significant. The concentration of fibrinogen increased after exposure to quartz diorite, while it decreased after exposures to rhomb porphyry and lactose. Type of material was a statistically significant explanatory variable for the concentration of fibrinogen, with the most significant increase occurring 24h post-exposure to quartz diorite. After exposure to the three materials, vWF decreased. For the thrombocytes, an increase in blood count was observed 24h post-exposure to quartz diorite and rhomb porphyry, with a modest (p=0.09) positive association for quartz diorite. Although the results are limited, we conclude that the different effects observed post-exposure to quartz diorite support considering potential health effects when choosing materials in the production of asphalt.

Performance of a whole-body human dust inhalation challenge exposure chamber.

BackgroundEvaluation of the performance of a whole-body human dust exposure chamber is presented in this report.MethodsThe volume of the chamber is 2.13 m3 and it is operated at a flow rate of 1.0 m3/min. Makeup and exhaust air were filtered. A Wright Dust Feeder was used to generate fly ash, the testing agent. An elutriator was used to maintain particles in the respirable range. A Rupprecht and Patashnick PM-10 TEOM, a direct reading instrument, was used to monitor particle concentration. Particle size distributions were determined by a QCM cascade impactor. The evenness of dust concentrations in the chamber was determined gravimetrically.ResultsDust concentrations measured at different points within the chamber were associated with variability less than 10%. Dust concentrations measured by the TEOM, in μg/m3, at 0.2, 0.4, 0.8 and 1.6 RPMs of the Wright Dust Feeder, were 110 ± 2.8, 173 ± 8.5, 398 ± 20 and 550 ± 17, respectively. Particle size distributions (MMD and GSD) were 1.27 μm and 2.35, 1.39 and 2.22, 1.46 and 2.08, 1.15 and 2.2, respectively. Total dust concentrations measured gravimetrically in μg/m3, were 135 ± 21, 200 ± 35, 333 ± 18 and 891 ± 27, respectively.ConclusionThe whole-body human exposure chamber offers several advantages and has better performance than most of the inhalation challenge systems previously described.

Performance of a human inhalation challenge exposure system. I. Gases

The purpose of this study was to characterize and evaluate the performance of a whole-body human exposure chamber for controlled test atmospheres of gases and particulates. This article is a report on the performance of the system with gas phase agents. Results of the performance of the system with particulate phase agents will be presented in a separate report. The chamber was constructed from Plexiglas with a volume of 2.13 m3 (75 ft3) and operating at a flow rate about 1.0 m3/min (34 cfm). Both the makeup and exhaust air were HEPA-filtered. CO2 was used as a tracer gas and its concentration was measured using Metrosonics aq-5000 instruments. The CO2 concentrations used in this study ranged from about 5000 to 12,000 ppm. Observed and predicted concentrations at equilibrium of test material were in agreement within 1.7%. Concentration of CO2 was found to be even horizontally throughout the chamber, with a small initial lag of about 30 sec between the maximum concentration at the top and the bottom of the chamber. The system can thus be reliably used for inhalation challenge procedures for gases.

Large Organic Aerosols in a Dynamic and Continuous Whole-Body Exposure Chamber Tested on Humans and on a Heated Mannequin

Exposure to large airborne organic aerosols may cause respiratory and skin symptoms. The use of human exposure chambers permits safe mechanistic studies of the effect of inhalation or dermal deposition of such particles. The performance of a dynamic and continuous whole-body human exposure chamber using turbulent air mixing during exposure to these organic aerosols of humans and of a new heated mannequin was evaluated. Variability of temporal and spatial distribution of the airborne particle concentration, and aerodynamic aerosol size distribution of the inhalable fraction, were evaluated. The temporal and spatial distribution of these aerosols close to the breathing zone during an exposure session was typically < or = 10%, which is low for airborne particles of this size. In a larger section around a human, only slightly higher spatial variation was found. Variability between exposure sessions was also low (< 10%). Only limited effect of relative humidity for the organic aerosols was observed. The aerodynamic particle size distribution curves differed slightly, but some were comparable to those in occupational environments. The outcome of the performance tests as measured with the heated mannequin was almost the same as with humans, indicating that the mannequin could be used in preparatory tests in this type of chamber.

Human Exposure Chamber for Known Formaldehyde Levels: Generation and Validation

Formaldehyde is a common air pollutant of the indoor environment. It has a potential effect on the respiratory function of people and so studies have been performed to assess this using exposure methods with high concentrations of formaldehyde. However, epidemiology studies have shown its impact on allergic diseases at lower domestic levels. The aim of this study was to develop an exposure chamber to study effects of low controlled concentrations of formaldehyde. Concentrations in the chamber were quantified by a simple DNHP-derivatisation method followed by liquid chromatography coupled to UV detection. Experiments to assess formaldehyde generation yield and reproducibility of formaldehyde levels in the chamber were performed in an empty chamber. The temporal decay of formaldehyde concentration in the exposure chamber was also investigated for more than 2h under different experimental conditions, for example in darkness or with somebody inside the chamber. Actual measured levels of formaldehyde were found to be 78-91% of the calculated value expected. The study of the temporal decay showed that subject’s breathing accounted for the fate of approximately 50% of the formaldehyde lost. Leaks, wall deposition, photolysis and adsorption on clothes were processes identified to explain the remaining 50%. However, this study has shown that both homogeneity and stability of formaldehyde concentration in the gas phase can be maintained acceptably to carry out future human exposure experiments.

Characterization of an Ambient Coarse Particle Concentrator Used for Human Exposure Studies: Aerosol Size Distributions, Chemical Composition, and Concentration Enrichment

The goals of the experiments described herein involve determining in real time the size, concentration enrichment, and chemical composition of coarse-mode ( 2.5 μm) particles within the nonconcentrated and concentrated flows of a coarse particle concentrator used for human exposure studies. The coarse particle concentrator was intended to concentrate ambient particles in the PM10–2.5 size range before sending them into a human exposure chamber. The aerodynamic size and chemical composition of particles in the upstream and downstream flows of the concentrator were monitored with an aerosol time-of-f1ight mass spectrometer (ATOFMS) for fixed time intervals over the course of three days. Based on the ATOFMS results, it was found that there was no change in the composition of the ten major particle types observed in the upstream and downstream flows of the concentrator under normal operating conditions. Furthermore, no new particle types were detected downstream that were not detected ...

Turbulent Three-Dimensional Air Flow and Trace Gas Distribution in an Inhalation Test Chamber

Steady incompressible turbulent air flow and transient carbon monoxide transport in an empty Rochester-style human exposure chamber have been numerically simulated and compared with experimental data sets. The system consisted of an inlet duct with a continuous carbon monoxide point source, 45- and 90-degree bends, a round diffuser, a round-to-square transition, a rectangular diffuser, the test chamber, a perforated floor, and again transition pieces from the chamber to an outlet duct. Such a configuration induced highly nonuniform vortical flow patterns in the chamber test area where a pollutant concentration is required to be constant at breathing level for safe and accurate inhalation studies. Presented are validated momentum and mass transfer results for this large-scale system with the main goals of determining the development of tracer gas (CO) distributions in the chamber and analyzing the contributions to CO-mixing. Numerical simulations were conducted employing a k-ε model and the latest available RNG k-ε model for air and CO-mixing. Both models predict similar velocity fields and are in good agreement with measured steady and transient CO-concentrations. It was found that secondary flows in the inlet section and strong vortical flow in the chamber with perforated flooring contributed to effective mixing of the trace gas at breathing levels. Specifically, in the height range of 1.4 m&lt;h&lt;2.0 m above the chamber floor, predicted CO-concentrations rapidly reached a near constant value which agrees well with experimental results. This work can be extended to analyze trace gas mixing as well as aerosol dispersion in occupied test chambers with or without flow redirection devices installed in the upstream section. A complementary application is particle transport and deposition in clean rooms of the electronic, pharmaceutical, and health care industries. [S0098-2202(00)01702-8]

Generation and Measurement of Formaldehyde in Exposure Chambers

A formaldehyde (HCHO) generation system suitable for animal and human inhalation studies has been constructed and employed in a large scale human exposure chamber at the University of Maryland School of Medicine. The generation system employs modified industrial hygiene calibration manifolds to vaporize paraformaldehyde to form monomeric HCHO. Generated concentrations of HCHO were maintainable within ±5% of the target concentrations. Measurement of HCHO levels in the exposure chamber has demonstrated a close correlation (r2=.981) between the NIOSH chromotrophic acid technique and TGM-555 monitors over the range of 0.5 to 3.0 ppm, with the impinger-chromotrophic acid technique yielding an average of 95% of the TGM-555 measurements.

Generation and Measurement of Formaldehyde in Exposure Chambers

A formaldehyde (HCHO) generation system suitable for animal and human inhalation studies has been constructed and employed in a large scale human exposure chamber at the University of Maryland School of Medicine. The generation system employs modified industrial hygiene calibration manifolds to vaporize paraformaldehyde to form monomeric HCHO. Generated concentrations of HCHO were maintainable within ±5% of the target concentrations. Measurement of HCHO levels in the exposure chamber has demonstrated a close correlation (r2=.981) between the NIOSH chromotrophic acid technique and TGM-555 monitors over the range of 0.5 to 3.0 ppm, with the impinger-chromotrophic acid technique yielding an average of 95% of the TGM-555 measurements.

The effects of continuous exposure to carbon monoxide on auditory vigilance in man.

Six different groups of non-smoking young male subjects were studied separately for 18 consecutive days each in a closed controlled-environmental human exposure chamber. Each group was subjected to a 5-day control period in fresh air followed successively by an 8-day period of continuous exposure to 50 ppm, 15 ppm or 0 ppm (control) by volume of carbon monoxide (CO) in air, and a 5-day recovery period in fresh air. The subjects performed a 1-h auditory vigilance task every day at the same time of day in a fixed qualitative, quantitative, and temporal relationship with food intake, consumption of stimulating beverages, physical activity, and sleep. It was concluded that such CO exposure, involving the continuous carriage of carboxyhaemoglobin loads up to 7%, was without significant effect on auditory vigilance.