Cadmium and lung cancer mortality accounting for simultaneous arsenic exposure.

OBJECTIVES: Prior investigations identified an association between airborne cadmium and lung cancer but questions remain regarding confounding by arsenic, a well-established lung carcinogen. METHODS: A cadmium smelter population exhibiting excess lung cancer was re-analysed using a retrospective exposure assessment for arsenic (As), updated mortality (1940-2002), a revised cadmium (Cd) exposure matrix and improved work history information. RESULTS: Cumulative exposure metrics for both cadmium and arsenic were strongly associated making estimation of their independent effects difficult. Standardised mortality ratios (SMRs) were modelled with Poisson regression with the contribution of arsenic to lung cancer risk constrained by exposure-response estimates previously reported. The results demonstrate (1) a statistically significant effect of Cd independent of As (SMR=3.2 for 10 mg-year/m(3) Cd, p=0.012), (2) a substantial healthy worker effect for lung cancer (for unexposed workers, SMR=0.69) and (3) a large deficit in lung cancer mortality among Hispanic workers (SMR=0.27, p=0.009), known to have low lung cancer rates. A supralinear dose-rate effect was observed (contribution to risk with increasing exposure intensity has declining positive slope). Lung cancer mortality was somewhat better predicted using a cadmium burden metric with a half-life of about 20-25 years. CONCLUSIONS: These findings support an independent effect for cadmium in risk of lung cancer mortality. 1/1000 excess lifetime risk of lung cancer death is predicted from an airborne exposure of about 2.4 µg/m(3) Cd.

Update of the NIOSH life table analysis system: a person-years analysis program for the windows computing environment.

BACKGROUND: Person-years analysis is a fundamental tool of occupational epidemiology. A life table analysis system (LTAS), previously developed by the National Institute for Occupational Safety and Health, was limited by its platform and analysis and reporting capabilities. We describe the updating of LTAS for the Windows operating system (LTAS.NET) with improved properties. SOFTWARE DEVELOPMENT PROCESS: A group of epidemiologists, programmers, and statisticians developed software, platform, and computing requirements. Statistical methods include the use of (indirectly) standardized mortality ratios, (directly) standardized rate ratios, confidence intervals, and P values based on the normal approximation and exact Poisson methods, and a trend estimator for linear exposure-response associations. SOFTWARE FEATURES: We show examples using LTAS.NET to stratify and analyze multiple fixed and time-dependent variables. Data import, stratification, and reporting options are highly flexible. Users may export stratified data for Poisson regression modeling. CONCLUSIONS: LTAS.NET incorporates improvements that will facilitate more complex person-years analysis of occupational cohort data.

Cohort mortality study of workers at seven beryllium processing plants: update and associations with cumulative and maximum exposure.

OBJECTIVES: To extend follow-up of cause-specific mortality in workers at seven beryllium processing plants and to estimate associations between mortality risk and beryllium exposure. METHODS: 9199 workers were followed for mortality from 1940 through 2005. Standardised mortality ratios (SMRs) were estimated based on US population comparisons for lung, nervous system and urinary tract cancers, chronic obstructive pulmonary disease (COPD), chronic kidney disease, and categories containing chronic beryllium disease (CBD) and cor pulmonale. Associations with maximum and cumulative exposure were calculated for a subset of the workers. RESULTS: Overall mortality in the cohort compared with the US population was elevated for lung cancer (SMR 1.17; 95% CI 1.08 to 1.28), COPD (SMR 1.23; 95% CI 1.13 to 1.32), and the categories containing CBD (SMR 7.80; 95% CI 6.26 to 9.60) and cor pulmonale (SMR 1.17; 95% CI 1.08 to 1.26). Mortality rates for most diseases of interest increased with time-since-hire. For the category including CBD, rates were substantially elevated compared to the US population across all exposure groups. Workers whose maximum beryllium exposure was ≥ 10 µg/m(3) had higher rates of lung cancer, urinary tract cancer, COPD and the category containing cor pulmonale than workers with lower exposure. Significant positive trends with cumulative exposure were observed for nervous system cancers (p = 0.0006) and, when short-term workers were excluded, lung cancer (p = 0.01), urinary tract cancer (p = 0.003) and COPD (p < 0.0001). CONCLUSION: These findings reaffirm that lung cancer and CBD, and suggest that COPD and nervous system and urinary tract cancers, are related to beryllium exposure. Cigarette smoking and exposure to other lung carcinogens are unlikely to explain these elevations.

High dietary niacin intake is associated with decreased chromosome translocation frequency in airline pilots.

Experimental studies suggest that B vitamins such as niacin, folate, riboflavin, vitamin B6 and vitamin B12 may protect against DNA damage induced by ionising radiation (IR). However, to date, data from IR-exposed human populations are not available. We examined the intakes of these B vitamins and their food sources in relation to the frequency of chromosome translocations as a biomarker of cumulative DNA damage, in eighty-two male airline pilots. Dietary intakes were estimated by using a self-administered semi-quantitative FFQ. Translocations in peripheral blood lymphocytes were scored by using fluorescence in situ hybridisation whole-chromosome painting. Negative binomial regression was used to estimate rate ratios and 95 % CI, adjusted for age and occupational and lifestyle factors. We observed a significant inverse association between translocation frequency and dietary intake of niacin (P = 0·02): adjusted rate ratio for subjects in the highest tertile compared with the lowest tertile was 0·58 (95 % CI 0·40, 0·83). Translocation frequency was not associated with total niacin intake from food and supplements as well as dietary or total intake of folate, riboflavin or vitamin B6 or B12. However, the adjusted rate ratios were significant for subjects with ≥ median compared with < median intake of whole grains (P = 0·03) and red and processed meat (P = 0·01): 0·69 (95 % CI 0·50, 0·96) and 1·56 (95 % CI 1·13, 2·16), respectively. Our data suggest that a high intake of niacin from food or a diet high in whole grains but low in red and processed meat may protect against cumulative DNA damage in IR-exposed persons.

Mortality and end-stage renal disease incidence among dry cleaning workers.

OBJECTIVE: Perchloroethylene (PCE) is a known animal carcinogen and probable human carcinogen. Dry cleaning exposures, particularly PCE, are also associated with renal toxicity. The objective was to follow-up a cohort of dry cleaners to evaluate mortality and assess end-stage renal disease (ESRD) morbidity. METHODS: This study adds 8 years of mortality follow-up for 1704 dry cleaning workers in four cities. Employees eligible for inclusion worked for ≥1 year before 1960 in a shop using PCE as the primary solvent. Life table analyses for mortality and ESRD morbidity were conducted. Only employees alive on 1 January 1977 were included in ESRD analyses. RESULTS: Overall cancer deaths were in significant excess in this cohort (standardised mortality ratio (SMR) 1.22, 95% CI 1.09 to 1.36). Oesophageal, lung and tongue cancers had significant excesses of deaths. Oesophageal cancer risk was highest among those employed in a PCE-using shop for ≥5 years with ≥20 years' latency since first such employment. Deaths from non-malignant underlying diseases of the stomach and duodenum were in significant excess. Hypertensive ESRD morbidity was significantly elevated in the entire cohort (standardised incidence ratio (SIR) 1.98, 95% CI 1.11 to 3.27), and among workers employed only in PCE-using dry cleaning shops for ≥5 years. CONCLUSION: Employment in the dry cleaning industry and occupational exposure to PCE are associated with an increased risk for ESRD and for cancer at several sites. The employment duration findings for oesophageal cancer and hypertensive ESRD further support an association with PCE exposure instead of lifestyle or socioeconomic factors.

Risk of lung cancer associated with quantitative beryllium exposure metrics within an occupational cohort.

OBJECTIVES: Beryllium has been identified as a human carcinogen on the basis of animal and epidemiological studies. The authors recently reported updated associations between lung cancer and beryllium exposure in a large, pooled occupational cohort. The authors conducted the present study to evaluate the shape of exposure-response associations between different exposure metrics and lung cancer in this cohort, considering potential confounders (race, plant, professional and short-term work status, and exposure to other lung carcinogens). METHODS: The authors conducted Cox proportional hazards regression analyses of lung cancer risk with cumulative, mean and maximum 'daily weighted average' (DWA) exposure among 5436 workers, using age-based risk sets. Different exposure-response curves were fitted to the exposure metrics, including categorical, power, restricted cubic spline and piecewise log-linear fits. RESULTS: The authors found significant positive associations between lung cancer and mean (p < 0.0001) and maximum (p < 0.0001) exposure, adjusting for age, birth cohort and plant, and for cumulative (p = 0.0017) beryllium exposure, adjusting for these factors plus short-term work status and exposure to asbestos. The best-fitting models were generally categorical or piecewise log-linear, with the steepest increase in lung cancer risk between 0 and 10 µg/m(3) for both mean and maximum DWA exposure and between 0 and 200 µg/m(3)-days for cumulative DWA exposure. The estimated mean DWA beryllium exposure associated with 10(-3) excess lifetime risk based on the piecewise log-linear model is 0.033 µg/m(3). CONCLUSION: This study provides evidence that lung cancer risk is elevated at levels near the current US Occupational Safety and Health Administration beryllium exposure limit of 2.0 µg/m(3) DWA for workers.

Mortality among members of a truck driver trade association.

Previous studies report that truck drivers are at increased risk for illness and on-the-job mortality. It is unknown whether owner-operator truck drivers face the same risks as employee drivers, yet few studies have targeted owner-operators as a study population. This study examined the overall and cause-specific mortality ratios for a cohort with owner-operator truck drivers constituting 69% of the study population. Of the 26 major disease classifications and 92 specific causes of death examined, only mortality due to transportation accidents was significantly elevated (standardized mortality ratio=1.52, 95% confidence interval=1.36-1.70). Leading causes of death were ischemic heart disease and lung cancer, although risk was below that of the general population. Transportation accidents pose a particular hazard for members of the trade association. The absence of excess disease mortality deserves careful interpretation, and may be due to both a strong healthy worker effect and a short monitoring period.

Bromide and N-acetyl-S-(n-propyl)-L-cysteine in urine from workers exposed to 1-bromopropane solvents from vapor degreasing or adhesive manufacturing.

OBJECTIVES: 1-Bromopropane (1-BP) is an alternative for ozone depleting and other solvents; it is used in aerosol products, adhesives, and cleaning solvents. There is concern that 1-BP may be a reproductive and neurological toxicant. Mercapturic acid conjugates are excreted in urine from 1-BP metabolism involving debromination. The main objectives were to evaluate urinary bromide [Br(-)] and N-acetyl-S-(n-propyl)-L-cysteine (AcPrCys) for assessing 1-BP exposure in workers with low exposure. METHODS: Workers' 1-BP exposures were measured in their breathing zones with gas chromatography-flame ionization detection via NIOSH 1025. Urine specimens were obtained over a 48-h period at five facilities using vapor degreasers and one adhesive manufacturer. All of the workers' urine was collected into composite samples and analyzed separately representing daily time intervals: at work, after work but before bedtime, and upon awakening. Urinary metabolites were analyzed using intra-coupled plasma-mass spectroscopy for Br(-), and high-performance liquid chromatography and electro-spray ionization mass spectroscopy for AcPrCys. RESULTS: Time-weighted average (TWA) geometric mean (GM) breathing zone concentrations of 1-BP at vapor degreasing facilities were 2.6 and 0.31 ppm, respectively, for workers near degreasers and those remote from degreasers. Urine metabolites showed the same trend as TWA exposures: higher levels were observed for workers near degreasers (48-h GM Br(-) = 8.9 vs. 3.7; 48-h GM AcPrCys = 1.3 vs. 0.12, respectively). Associations of Br(-) and AcPrCys concentrations with 1-BP TWA were statistically significant near degreasers (p < 0.01). CONCLUSIONS: This study shows that urinary Br(-) and AcPrCys are useful biomarkers of workers' 1-BP exposures using analyses sensitive enough to measure low exposure jobs.

High dietary antioxidant intakes are associated with decreased chromosome translocation frequency in airline pilots.

BACKGROUND: Dietary antioxidants may protect against DNA damage induced by endogenous and exogenous sources, including ionizing radiation (IR), but data from IR-exposed human populations are limited. OBJECTIVE: The objective was to examine the association between the frequency of chromosome translocations, as a biomarker of cumulative DNA damage, and intakes of vitamins C and E and carotenoids in 82 male airline pilots. DESIGN: Dietary intakes were estimated by using a self-administered semiquantitative food-frequency questionnaire. Translocations were scored by using fluorescence in situ hybridization with whole chromosome paints. Negative binomial regression was used to estimate rate ratios and 95% CIs, adjusted for potential confounders. RESULTS: Significant and inverse associations were observed between translocation frequency and intakes of vitamin C, beta-carotene, beta-cryptoxanthin, and lutein-zeaxanthin from food (P < 0.05). Translocation frequency was not associated with the intake of vitamin E, alpha-carotene, or lycopene from food; total vitamin C or E from food and supplements; or vitamin C or E or multivitamin supplements. The adjusted rate ratios (95% CI) for > or =median compared with or =median compared with

N-acetyl-S-(n-propyl)-l-cysteine in urine from workers exposed to 1-bromopropane in foam cushion spray adhesives.

1-Bromopropane (1-BP) has been marketed as an alternative for ozone depleting and other solvents; it is used in aerosol products, adhesives, metal, precision, and electronics cleaning solvents. Mechanisms of toxicity of 1-BP are not fully understood, but it may be a neurological and reproductive toxicant. Sparse exposure information prompted this study using 1-BP air sampling and urinary metabolites. Mercapturic acid conjugates are excreted in urine from 1-BP metabolism involving debromination. Research objectives were to evaluate the utility of urinary N-acetyl-S-(n-propyl)-L-cysteine (AcPrCys) for assessing exposure to 1-BP and compare it to urinary bromide [Br((-))] previously reported for these workers. Forty-eight-hour urine specimens were obtained from 30 workers at two factories where 1-BP spray adhesives were used to construct polyurethane foam seat cushions. Urine specimens were also obtained from 21 unexposed control subjects. All the workers' urine was collected into composite samples representing three time intervals: at work, after work but before bedtime, and upon awakening. Time-weighted average (TWA) geometric mean breathing zone concentrations were 92.4 and 10.5 p.p.m. for spraying and non-spraying jobs, respectively. Urinary AcPrCys showed the same trend as TWA exposures to 1-BP: higher levels were observed for sprayers. Associations of AcPrCys concentrations, adjusted for creatinine, with 1-BP TWA exposure were statistically significant for both sprayers (P < 0.05) and non-sprayers (P < 0.01). Spearman correlation coefficients for AcPrCys and Br((-)) analyses determined from the same urine specimens were highly correlated (P < 0.0001). This study confirms that urinary AcPrCys is an important 1-BP metabolite and an effective biomarker for highly exposed foam cushion workers.

Presence of tungsten-containing fibers in tungsten refining and manufacturing processes.

In tungsten refining and manufacturing processes, a series of tungsten oxides are typically formed as intermediates in the production of tungsten powder. The present study was conducted to characterize airborne tungsten-containing fiber dimensions, elemental composition and concentrations in the US tungsten refining and manufacturing industry. During the course of normal employee work activities, seven personal breathing zone and 62 area air samples were collected and analyzed using National Institute for Occupational Safety and Health (NIOSH) fiber sampling and counting methods to determine dimensions, composition and airborne concentrations of fibers. Mixed models were used to identify relationships between potential determinants and airborne fiber concentrations. Results from transmission electron microscopy analyses indicated that airborne fibers with length >0.5 microm, diameter >0.01 microm and aspect ratios > or =3:1 were present on 35 of the 69 air samples collected. Overall, the airborne fibers detected had a geometric mean length approximately 3 microm and diameter approximately 0.3 microm. Ninety-seven percent of the airborne fibers identified were in the thoracic fraction (i.e. aerodynamic diameter < or = 10 microm). Energy dispersive X-ray spectrometry results indicated that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Based on NIOSH fiber counting 'B' rules (length > 5 microm, diameter < 3 microm and aspect ratio > or = 5:1), airborne fiber concentrations ranged from below the limit of detection to 0.085 fibers cm(-3), with calcining being associated with the highest airborne concentrations. The mixed model procedure indicated that process temperature had a marginally significant relationship to airborne fiber concentration. This finding was expected since heated processes such as calcining created the highest airborne fiber concentrations. The finding of airborne tungsten-containing fibers in this occupational setting needs to be confirmed in similar settings and demonstrates the need to obtain information on the durability and associated health effects of these fibers.

Biological exposure assessment to tetrachloroethylene for workers in the dry cleaning industry.

BACKGROUND: The purpose of this study was to assess the feasibility of conducting biological tetrachloroethylene (perchloroethylene, PCE) exposure assessments of dry cleaning employees in conjunction with evaluation of possible PCE health effects. METHODS: Eighteen women from four dry cleaning facilities in southwestern Ohio were monitored in a pilot study of workers with PCE exposure. Personal breathing zone samples were collected from each employee on two consecutive work days. Biological monitoring included a single measurement of PCE in blood and multiple measurements of pre- and post-shift PCE in exhaled breath and trichloroacetic acid (TCA) in urine. RESULTS: Post-shift PCE in exhaled breath gradually increased throughout the work week. Statistically significant correlations were observed among the exposure indices. Decreases in PCE in exhaled breath and TCA in urine were observed after two days without exposure to PCE. A mixed-effects model identified statistically significant associations between PCE in exhaled breath and airborne PCE time weighted average (TWA) after adjusting for a random participant effect and fixed effects of time and body mass index. CONCLUSION: Although comprehensive, our sampling strategy was challenging to implement due to fluctuating work schedules and the number (pre- and post-shift on three consecutive days) and multiplicity (air, blood, exhaled breath, and urine) of samples collected. PCE in blood is the preferred biological index to monitor exposures, but may make recruitment difficult. PCE TWA sampling is an appropriate surrogate, although more field intensive. Repeated measures of exposure and mixed-effects modeling may be required for future studies due to high within-subject variability. Workers should be monitored over a long enough period of time to allow the use of a lag term.

A comparison of two methods for estimating prevalence ratios.

BACKGROUND: It is usually preferable to model and estimate prevalence ratios instead of odds ratios in cross-sectional studies when diseases or injuries are not rare. Problems with existing methods of modeling prevalence ratios include lack of convergence, overestimated standard errors, and extrapolation of simple univariate formulas to multivariable models. We compare two of the newer methods using simulated data and real data from SAS online examples. METHODS: The Robust Poisson method, which uses the Poisson distribution and a sandwich variance estimator, is compared to the log-binomial method, which uses the binomial distribution to obtain maximum likelihood estimates, using computer simulations and real data. RESULTS: For very high prevalences and moderate sample size, the Robust Poisson method yields less biased estimates of the prevalence ratios than the log-binomial method. However, for moderate prevalences and moderate sample size, the log-binomial method yields slightly less biased estimates than the Robust Poisson method. In nearly all cases, the log-binomial method yielded slightly higher power and smaller standard errors than the Robust Poisson method. CONCLUSION: Although the Robust Poisson often gives reasonable estimates of the prevalence ratio and is very easy to use, the log-binomial method results in less bias in most common situations, and because it fits the correct model and obtains maximum likelihood estimates, it generally results in slightly higher power, smaller standard errors, and, unlike the Robust Poisson, it always yields estimated prevalences between zero and one.

Ethnic, racial, and gender variations in health among farm operators in the United States.

PURPOSE: The purpose of this study was to collect baseline prevalence data on the health problems faced by minority, white, and female farm operators. METHODS: An occupational health survey of farm operators was conducted by the U.S. Department of Agriculture, National Agricultural Statistics Service between February and August 2000. A stratified random sample of farm operators from 50 U.S. states based on the 1997 Census of Agriculture was selected for telephone interview. Interviews were primarily conducted using a computer assisted telephone instrument system. RESULTS: Population prevalences were calculated for 7137 farm operators. Prevalences were greatest for musculoskeletal discomfort, followed by respiratory problems, hearing loss, and hypertension. Generally, Latino and Asian American operators had lower prevalences for health problems than white non-Latino and white operators, respectively. African-American operators had greater prevalences for hypertension, and osteoarthritis, but lower prevalences for hearing loss, skin problems, heart problems, and cancer than white operators. American Indian or Alaska Native operators had higher prevalences for musculoskeletal problems, skin problems, and hypertension. CONCLUSIONS: Prevalences for the different ethnicity and race groups are not the same. Studies that combine racial and ethnic groups, or study only white and non-Latino farm operators may overestimate or underestimate the prevalence of health conditions in the entire farm operator population.

The suicide mortality of working physicians and dentists.

BACKGROUND: Some studies have shown that physicians and dentists have elevated risks of suicide, while other studies have not. AIMS: Using all deaths and corresponding census data in 26 US states, we examine the suicide risk for working physicians and dentists. METHODS: Death and census data for working people were obtained from 1984 through 1992. Directly age-standardized suicide rate ratios (SRRs) were calculated for white male and white female physicians and white male dentists. RESULTS: For white female physicians, the suicide rate was elevated compared to the working US population (SRR = 2.39, 95% CI = 1.52-3.77). For white male physicians and dentists, the overall suicide rates were reduced (SRR = 0.80, 95% CI = 0.53-1.20 and 0.68, 95% CI = 0.52-0.89, respectively). For older white male physicians and dentists, however, observed suicide rates were elevated. CONCLUSIONS: White female physicians have an elevated suicide rate. Only older white male physicians and dentists have elevated suicide rates, which partially explains the varied conclusions in the literature.

Race, occupation, and lung cancer: detecting disparities with death certificate data.

OBJECTIVES: To determine whether the analysis of death certificate data would reveal the same relationship among race, occupational exposure, and lung cancer mortality observed by a large cohort study. METHODS: An occupation-specific mortality odds ratio (MOR) for lung cancer (ICD-162) versus all other causes was calculated for 218,341 black men and white men who had been employed in the metal industries. RESULTS: Black men were at increased risk for lung cancer mortality when compared with white men among the 4668 oven workers (MOR = 1.38, 95% CI = 1.10 to 1.73), but not among the 33,605 white-collar workers (MOR = 0.95, 95% CI = 0.74 to 1.23). CONCLUSIONS: Our findings corroborate a previously demonstrated association among exposure to carcinogenic coke oven emissions, race, and lung cancer mortality, and support the use of death certificate data to help identify occupations with racial disparities in lung cancer mortality.

Evaluation of a proposed area equation for improved exothermic process control.

Our understanding of heat transfer and meteorological theories and their applications for engineering control design have been refined since the collective work in ventilation engineering for manufacturing process was published by Hemeon in 1955. These refined theories were reviewed and used to develop a newly proposed equation to estimate buoyant plume area (A). The area is a key parameter in estimating the plume volumetric flow (Q=UA) required for exothermic process control. Subsequent to developing a theoretical equation for plume area (A), plume velocity and area data were collected in the laboratory using a thermal anemometer and a scale-model exothermic process. Laboratory results were compared to solutions provided by the proposed, American Conference of Governmental Industrial Hygienists (ACGIH) and Hemeon plume area equations to determine which equation most closely matched the laboratory data. To make this determination, either t-tests or Wilcoxon signed-rank tests were conducted (based on examination of data normality) to determine the difference between collected data and solutions from the proposed, ACGIH and Hemeon equations. Median differences and P-values from Wilcoxon signed-rank tests (non-parametric) indicate that the ACGIH and Hemeon plume area equations provide significantly lower values than the laboratory data. However, the proposed equation provided solutions that were not significantly different from the collected data. Results indicate that the plume area equations currently recommended by the ACGIH and Hemeon are not as accurate as the proposed equation over the range of parameters investigated.

Evaluation of a proposed velocity equation for improved exothermic process control.

Exothermic or heated processes create potentially unsafe work environments for an estimated 5-10 million American workers each year. Excessive heat and process contaminants have the potential to cause adverse health effects in exposed workers. Owing to the potential hazards, engineering controls are recommended for these processes. Our understanding of heat transfer and meteorological theories, and their applications for engineering controls have evolved since seminal work was published by Hemeon in 1955. These refined theories were reviewed and used to develop a proposed equation to estimate buoyant plume mean velocity. Mean velocity is a key parameter used to estimate the plume volumetric flow required for controlling effluents from exothermic processes. Subsequent to developing the proposed equation, plume velocity data were collected with a thermal anemometer for a model exothermic process in the laboratory, and an actual exothermic process in the field. Laboratory and field results were then compared to solutions provided by the proposed, American Conference of Governmental Industrial Hygienists (ACGIH), and Hemeon mean velocity equations. To determine which equation most closely matched the laboratory and field data, either t-tests or Wilcoxon Signed Rank tests were conducted (based on examination of data normality) to determine the difference between collected data and solutions from the proposed, ACGIH, and Hemeon equations. Median differences and P-values from Wilcoxon Signed Rank tests (nonparametric) indicate that the ACGIH mean velocity equation provides significantly different estimates from the laboratory and the field mean velocity data. However, the proposed and Hemeon equation provided solutions that were not significantly different from the collected data. These results were unexpected due to the similar developmental backgrounds between the ACGIH and Hemeon equations. Findings indicate that radiant heat flux is an important consideration when using horizontal plate heat transfer equations to estimate plume mean velocity over the range of parameters investigated. Results indicate that the mean velocity equation currently recommended by ACGIH is not as accurate as either the proposed or Hemeon equations over the range of parameters investigated.