Biomedical subjects

Michael R Flynn

Publications and source records attributed to Michael R Flynn.

13 recordsLinked to original sources

PubMed2006

Fitting human exposure data with the Johnson S(B) distribution.

Exposure evaluations for epidemiological investigations and risk assessments may require estimates of background concentrations and peak exposures, as well as the population mean and variance. The S(B) distribution is a theoretically appealing probability function for characterizing ratios, and random variables bound by extremes, such as human exposures and environmental concentrations. However, fitting the parameters of this distribution with maximum likelihood methods is often problematic, and some alternative methods are examined here. Two methods based on percentiles, a quantile estimator, and a method-of-moments fitting procedure are explored. The quantile and method-of-moments procedures are based on new explicit expressions for the first four moments of this distribution. The fitting procedures are compared by simulation, and with actual data sets consisting of measurements of human exposure to airborne contaminants.

Environmental Exposure↗

PubMed2006

Modeling dermal exposure--an illustration for spray painting applications.

This article presents a conceptual, mathematical model of dermal exposure resulting from aerosol deposition on human forearm hair. The model is applicable to exposure scenarios where dermal deposition is governed by aerosol impaction, interception, and diffusion mechanisms. The model employs filtration theory, single fiber efficiency equations, and a modified potential airflow approximation. The results are extended, using previously published results, for application to dermal deposition on the forearm during spray painting. The average (N = 8) predicted dermal deposition of 1,6-hexamethylene diisocyanate as collected on a 10-cm(2) tape strip is 108.9 (+/- 70.3) pmol, whereas field measurements indicated an average of 168.6 (+/- 82.0) pmol per strip. The corresponding measured average dermal flux was 3.63 pg/cm(2)s (+/- 1.34); the prediction was 2.24 pg/cm(2)sec (+/- 1.25). The study calls attention to the importance of body hair both for modeling and measuring dermal exposures.

Air Pollutants, Occupational↗

PubMed2005

CFD model for a 3-D inhaling mannequin: verification and validation.

This work investigates the use of computational fluid dynamics (CFD) to model air flow and particle transport associated with an inhaling anatomical mannequin. The studied condition is typically representative of occupational velocities (Re = 1920) and at-rest breathing (R = U(o)/U(m) = 0.11). Methods to verify and validate CFD simulations are detailed to demonstrate convergence and describe the model's uncertainties. The standard k-epsilon model provided a reasonable flow field, although vertical velocity components were consistently smaller than the experimental validation data, owing to truncation of the computational model at hip height. Laminar particle trajectory studies indicated that the modeled velocity field resulted in a shift of particle aspiration fractions toward particles smaller than those determined experimentally, consistent with the vertical velocity field differences.

Air Movements↗

PubMed2005

Evaluation of facial features on particle inhalation.

Computational fluid dynamics (CFD) and numerical investigations of particle inhalability and contaminant exposure have used simple geometrical surrogates for a breathing human form, but the effect of eliminating facial features has not been investigated. In this work, the velocity field and particle aspiration associated with two differently shaped mannequins were investigated to determine if an elliptical form was sufficient to represent the complexity of fluid flow associated with an inhaling human. Laser Doppler anemometry was used to measure velocity, and both optical sizing and gravimetric analysis were used to measure particle aspiration from an aerosol source. All tests were performed with continuous inhalation through the mouth, with the mannequin facing the 0.3 m s(-1) freestream. Although limitations in the laser Doppler optics prevented velocity measurements at distances <11 mm in front of the mannequin mouth opening, significant velocity differences were identified up to 20 mm in front of the mouth opening. This indicated that facial features affected the flow field near the face only. Owing to these differences, particle aspiration was compared between mannequins for three different velocity ratio conditions using an aerosol source. Even with relatively large variability in the aspirated concentration in this study, the aspirated mass concentration was significantly less for the anatomical mannequin relative to the elliptical form. Thus, the simplified elliptical cylinder does not sufficiently characterize the fluid dynamics near the mouth of an inhaling human form at these limited test conditions. Future CFD and numerical simulations to investigate human aspiration of particles should incorporate the complex features of the human face to investigate adequately particle aspiration in low velocity environments.

Air Movements↗

PubMed2004

The 4-parameter lognormal (SB) model of human exposure.

This paper explores the 4-parameter lognormal distribution (or Johnson S(B) distribution) as a model for occupational exposures to airborne contaminants. This model can incorporate extreme values when they are known a priori, or alternatively, they can be estimated from the data. This additional flexibility may be of value in estimating background and/or maximum exposures, as well as improving the fitting process and subsequent estimation of mean exposures. In addition, the model is physically consistent with the definition of concentration and provides a basis for linking stochastic and deterministic exposure modeling approaches. There is some additional computational burden in estimating the mean and variance of exposure relative to the usual 2-parameter lognormal model.

Air Pollutants, Occupational↗

PubMed2004

A stochastic differential equation for exposure yields a beta distribution.

This paper presents a stochastic differential equation for exposure based on a modified version of the standard dilution ventilation equation. An equilibrium solution is obtained with the assumption that variability in the rate of change of concentration is proportional to the product of concentration and one minus concentration. Appropriate definitions for concentration are used to ensure a physically consistent model. The probability distribution for exposure that results is the standard beta distribution. This model is supported by several exposure data sets, which fit the beta distribution well. Issues regarding parameter estimation for the beta distribution, and application of the model are presented. Recommendations are made for simultaneously collecting contaminant generation rate information, ventilation rates, and time-dependent breathing-zone tracer concentrations, in addition to the exposure data.

Air Pollutants↗

PubMed2004

A review of engineering control technology for exposures generated during abrasive blasting operations.

This literature review presents information on measures for controlling worker exposure to toxic airborne contaminants generated during abrasive blasting operations occurring primarily in the construction industry. The exposures of concern include respirable crystalline silica, lead, chromates, and other toxic metals. Unfortunately, silica sand continues to be widely used in the United States as an abrasive blasting medium, resulting in high exposures to operators and surrounding personnel. Recently, several alternative abrasives have emerged as potential substitutes for sand, but they seem to be underused Some of these abrasives may pose additional metal exposure hazards. In addition, several new and improved technologies offer promise for reducing or eliminating exposures; these include wet abrasive blasting, high-pressure water jetting, vacuum blasting, and automated/robotic systems. More research, particularly field studies, is needed to evaluate control interventions in this important and hazardous operation.

Construction Materials↗

PubMed2003

Engineering controls for selected silica and dust exposures in the construction industry--a review.

This literature review summarizes engineering control technology research for dust and silica exposures associated with selected tasks in the construction industry. Exposure to crystalline silica can cause silicosis and lung fibrosis, and evidence now links it with lung cancer. Of over 30 references identified and reviewed, 16 were particularly significant in providing data and analyses capable of documenting the efficacy of various engineering controls. These reports include information on generation rates and worker exposures to silica and dust during four different tasks: cutting brick and concrete block, grinding mortar from between bricks, drilling, and grinding concrete surfaces. The major controls are wet methods and local exhaust ventilation. The studies suggest that while the methods provide substantial exposure reductions, they may not reduce levels below the current ACGIH threshold limit value (TLV) of 0.05 mg/m(3) for respirable quartz. Although further research on controls for these operations is indicated, it is clear that effective methods exist for significant exposure reduction.

Air Pollutants, Occupational↗

PubMed2003

On the inertial range of particles under the influence of local exhaust hoods.

This paper presents results from numerical simulations conducted to estimate the inertial range (stopping distance) of large aerosol particles ejected away from local exhaust hoods. Potential flow theory is used to specify the air velocity along the centerline of a flanged circular hood. A high-order Gear method is used to integrate the particle equations of motion with drag coefficients in the transitional range. The results allow for a relative comparison of hood performance based on the energy cost needed to stop the particle within a specified distance. Hood size is shown to be a critical factor, while the capture velocity generated by the hood at the point of particle ejection is of secondary importance.

Aerosols↗

PubMed2002

Characterization of emissions from burning incense.

The primary objective of this study was to improve the characterization of particulate matter emissions from burning incense. Emissions of particulate matter were measured for 23 different types of incense using a cyclone/filter method. Emission rates for PM2.5 (particulate matter less than 2.5 microm in aerodynamic diameter) ranged from 7 to 202 mg/h, and PM2.5 emission factors ranged from 5 to 56 mg/g of incense burned. Emission rates were also determined using an electrical low pressure impactor (ELPI) and a small electrostatic precipitator (ESP), and emission rates were compared to those determined using the cyclone/filter method. Emission rates determined by the ELPI method were consistently lower than those determined by the cyclone/filter method, and a linear regression correlation was found between emission rates determined by the two methods. Emission rates determined by the ESP method were consistently higher than those determined by the cyclone/filter method, indicating that the ESP may be a more effective method for measuring semivolatile particle emissions. A linear regression correlation was also found between emission rates determined by the ESP and cyclone/filter methods. Particle size distributions were measured with the ELPI, and distributions were found to be similar for most types of incense that were tested. Size distributions by mass typically ranged from approximately 0.06 to 2.5 microm in aerodynamic diameter, with peak values between 0.26 and 0.65 microm. Results indicated that burning incense emits fine particulate matter in large quantities compared to other indoor sources. An indoor air quality model showed that indoor concentrations of PM25 can far exceed the outdoor concentrations specified by the US EPA's National Ambient Air Quality Standards (NAAQS), so incense smoke can pose a health risk to people due to inhalation exposure of particulate matter. Emissions of carbon monoxide (CO), nitric oxide (NO), and sulfur dioxide (SO2) were also measured for seven types of incense. Emission rates of the gaseous pollutants were sufficient to cause indoor concentrations, estimated using the indoor air quality model, to exceed the outdoor concentrations specified by the NAAQS under certain conditions. However, the incense samples that were tested would fill a room with thick smoke under these conditions.

Air Pollutants↗

PubMed2002

Methods for estimating the transfer efficiency of a compressed air spray gun.

The transfer efficiency of a compressed air spray gun is an important performance index with regard to worker health, environmental, and economic considerations. It is defined as the fraction of paint sprayed that coats the surface. Worker exposure has been identified as a function of the transfer efficiency based on total mass of paint sprayed, which can be predicted by a mathematical model developed with nonvolatile oil. This study extends the existing model to include volatile effects by employing a mathematical approach based on a mass balance. This method allows the current model to predict transfer efficiency bounds at two extreme situations: all volatile compounds evaporate either before or after droplet impaction. Model predictions show that tight transfer efficiency bounds are obtained, especially for high values of transfer efficiency. Thus, the average of the upper and lower bounds should be a reasonable estimate of transfer efficiency. It is also found that the current model prediction, which is based on total mass of paint sprayed, for nonvolatile material can be converted to a transfer efficiency based on the mass of solids. The laboratory study shows that the predicted transfer efficiency based on the mass of solids is within the 95 percent C.I. of the measured value. This work relates the transfer efficiency used in industry, which is calculated on the basis of paint solids, with a model that predicts worker exposure during spray painting operations.

Air Movements↗

PubMed2002

A field evaluation of the impact of transfer efficiency on worker exposure during spray painting.

This paper presents a mathematical model to predict breathing-zone overspray concentrations produced during spray painting as a function of the overspray generation rate, ventilation and work practices. The overspray generation rate required an estimate of the spray gun transfer efficiency, which was provided by a previously developed mathematical model. These models were evaluated in the field under two different scenarios: first in a controlled environment that approximated the assumptions of models, and then under actual spray painting conditions. Results from the first test showed the model overestimated transfer efficiency, but the measured exposures and predicted exposures were not significantly different. During actual spray painting operations, all task exposures were within a factor of three of the model predictions, and there was no statistical difference between the measured and predicted values. The predicted average exposure of each worker was within the 95% confidence interval. The overall mean exposure was within one standard error of the model prediction. The current study expands on the original exposure model by including a transfer efficiency model to provide a better estimate of the overspray generation rate. The theoretical foundation between exposure and its primary determinants is established, and this knowledge can be applied to design and can evaluate optimal control interventions. Also, the general methodology presented here for developing an exposure model is applicable to operations other than spray painting.

Aerosols↗

PubMedDate not supplied

Report of the Howard Hughes Medical Institute's workshop on the performance of laboratory chemical hoods.

The Howard Hughes Medical Institute sponsored a workshop on laboratory chemical hoods on June 8, 9, and 10, 1998, that brought together 24 experts in the field of laboratory chemical hoods to critically assess the information known about hood performance. Workshop participants developed 31 consensus statements that reflect their collective views on the body of knowledge or lack thereof, for laboratory chemical hoods. The consensus statements fall into four broad categories: (1) hood selection, use, and operation; (2) hood and laboratory design issues; (3) ventilation system design issues; and (4) hood performance testing. The consensus statements include 26 statements on what is known and unknown about the performance of laboratory chemical hoods, 2 statements of definition, and 3 statements that reflect the participants' agreement not to agree. The brief commentary that follows each consensus statement provides guidance and recommendations.

Certification↗