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Biomedical subjects

T E Bernard

Publications and source records attributed to T E Bernard.

16 recordsLinked to original sources
PubMed1999

Continuing the search for WBGT clothing adjustment factors.

The original concept for the heat stress limits adopted by the American Conference of Governmental Industrial Hygienists (ACGIH) was that the threshold for heat stress can be marked by environmental conditions (WBGT) that are adjusted for metabolic rate. The underlying data were based on ordinary work clothes. The Physical Agents Committee promoted clothing adjustment factors within the industrial hygiene community through a revision in the TLVs for heat stress in 1990. As approved, there were adjustment factors for three other clothing ensembles. To extend and further understand adjustment factors, adjustments for commercially available clothing ensembles and prototype ensembles have been examined. The fundamental principle of the assignment of an adjustment factor to an ensemble begins with establishing critical environmental conditions in which test subjects were just able to maintain thermal equilibrium. Four or five subjects for each ensemble walked on a tread-mill inside a climatic chamber under controlled conditions of heat stress. During each test, heart rate and core temperature were continuously monitored. After a physiological steady-state was achieved, temperature and humidity were slowly increased to maintain relative humidity at 20 percent, 50 percent, or 70 percent. Metabolic rate was assessed by measuring the rate of oxygen consumption. Reviewing a trial, the critical conditions were noted as the time when thermal regulatory control was lost (called the inflection point and marked by a steady increase in core temperature). The climatic conditions at the inflection point were used to assign a critical WBGT. A WBGT representative of each ensemble was assigned through a weighted average of different protocols. Clothing adjustment factors representing an equivalent increase in WBGT were computed by noting the difference between the representative WBGT of the cotton work clothes and the other clothing ensembles. The results suggested adjustment factors with reference to ordinary work clothes from the least stress at -2.1 to 5.5 degrees C-WBGT. The adjustment factors were reasonably well predicted by a linear regression based on a computed value for total evaporative resistance (r2 = 0.92).

Adult↗
PubMed1999

Prediction of workplace wet bulb global temperature.

The wet bulb globe temperature (WBGT) is the de facto standard to assess environmental contributions to heat stress. A practical problem emerges when the heat stress conditions vary over many locations or during the day. To address this problem, investigators have suggested empirical relationships and thermodynamic models. The purpose of this effort was to examine a thermodynamic model in the laboratory and to predict WBGTs in an aluminum smelter by both the empirical and thermodynamic models. In the laboratory, there was no real difference between the experimental data and the thermodynamic model. In the application to an aluminum smelter, there was a small overall tendency for the predicted values to be greater than the actual values, but there was no practical difference between the models. The empirical model provided a good match with a slight over-prediction by 0.5 degree C with a standard deviation of 3.0 degrees C. For the same data, the thermodynamic model had an average over-prediction of 0.7 degree C with a standard deviation of 2.8 degrees C. Either method of predicting WBGT was effective. The empirical method required less computation and was conceptually simpler.

Heat Stress Disorders↗
PubMed1999

Heat stress and protective clothing: an emerging approach from the United States.

There is little doubt that heat stress affects many workers adversely and that protective clothing generally adds to the burden. The ACGIH threshold limit value for heat stress is the guiding document for evaluation of heat stress in the United States. Adjustment factors have been used to reflect the change in heat stress imposed by different clothing ensembles. While the first proposed factors started with limited experimental data and professional judgment, heat balance methods in the laboratory have yielded better estimates of adjustment factors and for a wider selection of ensembles. These same experiments have provided the starting point to accounting for nonporous clothing in heat balance evaluation schemes such as required sweat rate. Proposed changes to the ACGIH TLV have been mentioned and a framework for thinking about controls presented.

Body Temperature Regulation↗
PubMed1994

Estimation of metabolic rate using qualitative job descriptors.

This project developed two methods to estimate metabolic rate that can be used easily and provide acceptable precision. The methods were developed from the measurement of oxygen consumption on 80 typical jobs in automotive manufacturing. The Ready-Reference Method uses three easily identified, dichotomous characteristics to classify the job into one of four levels of metabolic rate. The characteristics are based on motion of the hands, weights or forces, and walking; standard error of estimate was 68 kcal/hour. The Component Method has four terms that account for hand motion, walking/carrying, lifting, and pushing/pulling. Hand motions and lifting factors are characterized by three or four categories with a reference value to make the determination easier by using more qualitative data. Walking/carrying and pushing/pulling data are noted as typical distances traveled in one minute. The standard error of estimate for this method was 62 kcal/hour. In addition to a smaller standard error of estimate, the further advantage of the Component Method over the Ready-Reference Method is an ability to point toward the largest contributors to metabolic rate.

Automobiles↗
PubMed1994

Rationale for a personal monitor for heat strain.

Worker heat-stress exposures can be controlled for short periods above the threshold limit value (TLV) by self-assessment, if the worker can avoid overexposure based on excessive heart rate and/or excessive core temperature. A socially acceptable surrogate for core temperature and a measure of heart rate are objective measures that can increase the reliability of the self-assessment decision. This article describes a surface-mounted temperature sensor developed to indicate when rectal temperature reaches a safe limit. Protective criteria were established for temperature sensor alert limits. A fixed threshold for heart rate may cause premature alerts during bursts of activity and miss lower, but sustained, heart rates that represent significant physiological strain. For these reasons, heart rate criteria based on seven moving-time averages also were developed. The criteria are based on a relationship between heart rate and endurance time. The temperature sensor and heart rate criteria form the basis of a real-time personal monitor for heat strain.

Body Temperature↗
PubMed1993

Physiological evaluation of liquid-barrier, vapor-permeable protective clothing ensembles for work in hot environments.

Work clothes using fabrics with vapor-transmitting characteristics are in limited use in various industrial applications, and there is a growing interest in their purported ability to help reduce heat stress. This study was performed to compare two vapor-transmitting ensembles with other clothing ensembles previously tested. The evaluation was based on an established experimental protocol that determines the critical values of air temperature and water-vapor pressure so that an individual maintains thermal balance, while controlling other factors that contribute to worker heat stress (e.g., air motion and metabolism). There were no differences between the two vapor-transmitting garments in their effects on worker heat stress. When compared to the results of other studies, the two vapor-transmitting garments had critical environmental characteristics similar to two layers of cotton coveralls and they performed better from a heat stress standpoint than a disposable vapor-barrier suit worn over cloth coveralls.

Adult↗
PubMed1981

Modeling carbon monoxide uptake during work.

Acute carbon monoxide poisoning is the result of a diminished capacity of the blood to transport oxygen and sustain a level of metabolic activity. The diminished capacity is expressed in terms of the carboxyhemoglobin (COHb) level in the blood which is dependent upon the concentration of CO in the inhaled air. The rate of CO uptake or elimination is dependent upon the concentration of CO in the air as well as pulmonary diffusion capacity and alveolar ventilation which change with different metabolic rates. Coburn, Forster and Kane (CFK) developed a mathematical model to describe the uptake and elimination kinetics of CO in sedentary individuals. The CFK model was used in a mathematical simulation of CO uptake and elimination where the independent variables were inhaled CO concentration and metabolic rate. The metabolic rate was used to specify pulmonary diffusing capacity and alveolar ventilation. As the level of COHb increased the metabolic rate was decreased to a level compatible with the impaired oxygen transport. A physical fatigue limit was also included. The theoretical model was used to simulate conditions beyond the range of exposures permissible under experimental laboratory conditions.

Carbon Monoxide↗
PubMed1977

Evaluation of Federal man tests for self-contained breathing apparatus.

The transient pulmonary responses to four short duration man tests used in the Federal approval of breathing apparatus were measured. The pulmonary ventilation dropped 30 percent in the first thirty seconds in the periods assigned for samples and readings which were immediately preceded by work. A physiological deficit was incurred during the short duration man tests which meant that less O2 and ventilation were required when compared to steady state responses shown on approval tests. The scheduled man test activities for short duration breathing apparatus should be revised and made more vigorous to match the intended use of escape apparatus.

Adult↗
PubMed1977

Aspects of on-line digital integration of pulmonary gas transfer.

Digital computers are often used in work physiology to find pulmonary gas transfer on a breath-by-breath basis. A measurement procedure was simulated to determine the effects of sample rate, signal noise levels, and numerical filters on the digital calculations. The results indicated that a trapezoidal rule integration at a sample rate of 30 Hz with no numerical filter can provide satisfactory data. The flow rate and concentration signals should not be out of phase by more than 25 ms. The simple computational procedures give accurate results while minimizing the memory requirements and computation time.

Computers↗
PubMedDate not supplied

Thermal characteristics of clothing ensembles for use in heat stress analysis.

The Heat Stress Index was an early model for the assessment of heat stress. The International Organization for Standardization (ISO) standard for required sweat rate is the current generation of heat balance methods for occupational heat stress. The method assumes cotton clothing and works adequately for cotton/polyester blends. To extend the usefulness of the model, the thermal characteristics of a variety of commercially available and prototype protective clothing ensembles have been determined for application in the ISO method. The fundamental principle for assessing thermal characteristics of work clothing is establishing the critical environmental conditions in which test subjects were just able to maintain thermal equilibrium. Critical conditions were found for warm, humid conditions; hot, dry conditions; intermediate conditions of temperature and humidity; and/or moderate conditions in which metabolic rate was increased to a limiting thermal load. Typically, five subjects at each condition for each ensemble were used. Metabolic rate, average skin temperature, and the environmental conditions (air temperature and vapor pressure) were noted at the critical conditions, and the total insulation was estimated for each ensemble. From these values, the total evaporative resistance, the clothing factor for dry heat exchange (CFcl), and the clothing factor for evaporative cooling (CFpcl) were determined. When compared with reports of others on thermal characteristics the results agreed when pumping factors and clothing wetness were considered. The result was higher than expected values for CFcl and lower values for CFpcl.

Adult↗
PubMedDate not supplied

Heat stress and strain in an aluminum smelter.

Studies of worker heat stress and strain in aluminum smelters have found that heat exposure likely to exceed the American Conference of Governmental Industrial Hygienists' threshold limit value (TLV) and that the dose-response relationship between heat stress and strain was weak. A heat stress model based on climatic data and a task analysis indicated exposures to heat stress in excess of the TLV during the July/August study period. To study the impact of working above the TLV, heat strain data (i.e., oral temperature, recovery heart rate, average heart rate) were collected. Recovery heart rates indicated high strain most of the time, and oral temperatures after peak demands were above the no-strain threshold of 37.5 degrees C about a quarter of the time, indicating that heat stress had an effect. About 95% of the readings were below 38.0 degrees C, the acute oral temperature threshold for a safe exposure. Average heart rates over 6- and 12-hour intervals were generally below acceptable limits of 120 and 110 bpm, respectively. Oral temperature and average heart rates indicated good control of heat stress exposures. Because recovery heart rates were high, some employees were working near their individual limits. The dose-response relationship for recovery heart rate and oral temperature were examined against the level of heat stress above the TLV. There was no relationship between oral temperature and heat stress level. There was an apparent trend toward higher recovery heart rates with heat stress. The lack of a dose-response relationship may be explained by brief periods of very high wet bulb globe temperatures that drove the time-weighted average up out of proportion to the physiological response.

Aluminum↗