James T. Wassell

Assessment of perceived traumatic injury hazards during drywall hanging

Abstract Workers who handle massive and bulky drywall sheets are at a high risk of traumatic injuries. The objective of this study is to identify the drywall handling tasks and activities which are directly perceived as hazardous by workers. A questionnaire survey was conducted for the study. In the questionnaire, three hanging tasks were included: (1) hanging drywall on the ceiling; (2) hanging drywall on the upper half of the wall; and (3) hanging drywall on the lower half of the wall. Each of the three tasks was divided into 10 to 12 constituent activities. Supportive elevated equipment was also evaluated. Workers were instructed to rate the drywall-hanging tasks/activities and elevated equipment in regard to fall potential, perceived physical stress, and risk of being struck by or against objects, using a seven-point scale (1=hardly at all to 7=a great deal). Results from this study indicate that all the ratings of fall potential, perceived physical stress, and risk of being struck by or against objects while hanging drywall on the ceiling were greater than while performing the other two tasks. Activities involving lifting/carrying/holding drywall sheets were rated as most physically stressful. Workers perceived greatest physical stress and fall potential when wearing stilts as compared to using ladders or scaffolds. The findings of this study provide detailed information directly from the workers about the hazards associated with drywall hanging. Results from this study will assist in focusing future research efforts on the most hazardous tasks and activities of drywall hanging. Relevance to industry Construction workers who perform drywall installation have high occupational incident rate for traumatic injury. Handling massive and bulky drywall sheets increases the potential for physical stress, falls and struck by and against objects. A questionnaire was designed to collect injury information directly from construction workers who performed drywall hanging and to identify perceived hazards associated with drywall hanging. Prior to this study, there has been little substantive research to evaluate the excessive stresses imposed on this workforce.

POWER DETERMINATION FOR GEOGRAPHICALLY CLUSTERED DATA USING GENERALIZED ESTIMATING EQUATIONS

Study designs in public health research often require the estimation of intervention effects that have been applied to a cluster of subjects in a common geographic area, rather than randomly assigned to individual subjects, and where the outcome is dichotomous. Statistical methods that account for the intracluster correlation of measurements must be used or the standard errors of regression coefficients will be under-estimated. Generalized estimating equations (GEE) can be used to account for this correlation, although there are no straightforward methods to determine sample-size requirements for adequate power. A simulation study was performed to calculate power in a GEE model for a proposed study of the effect of an intervention, designed to reduce lower-back injuries among nursing personnel employed in nursing homes. Nursing homes will be randomly assigned to either an intervention or control group and all employees within a nursing home will be treated alike. Historical injury data indicates that the baseline-injury risk for each home can be reasonably modelled using a beta distribution. It is assumed that the risk for any individual nurse within a nursing home follows a Bernoulli probability distribution expressed as a logit function of fixed covariates, which have values of odds ratios determined from previous studies which represent characteristics of the study population, and a random-intercept term which is specific for each home. Results indicate that failure to account for intracluster correlation can lead to overestimates of power as well as inflation of type I error by as much as 20 per cent. Although the GEE method accounted for the intracluster correlation when present, estimates of the intracluster correlation were negatively biased when no intracluster correlation was present. In addition, and possibly related to the negatively biased estimates of intracluster correlation, we also found inflated type I error estimates from the GEE method.

The effect of wearing a back belt on spine kinematics during asymmetric lifting of large and small boxes

Study Design. A crossover design was used to evaluate kinematic measurements collected with an infrared-based motion measurement system. Objectives. To evaluate belt effects on spine kinematics during asymmetric lifting of large and small boxes and to test for carryover effects between trials from belts. Summary of Background Data. Conflicting evidence in the literature exists regarding whether belts are beneficial or detrimental to manual material handlers. Studies have not examined belt effects when lifting different sized boxes, nor carryover effects from belts. Methods. Twenty-eight subjects with manual-handling experience (17 male and 11 female) were randomly assigned to lift either a large or small box (weighing 9.4 kg), from a sagittally symmetric origin at pallet height to a 79 cm height, 60° to the right. Spine flexion, lateral bending and twisting, hip and knee flexion, and angular velocity measurements of the torso with respect to the pelvis were collected for each of three lifting periods, 50 lifts each at 3 lifts per minute, with 18-minute breaks between periods. Results. Belts significantly reduced maximum spine flexion, spine flexion and extension angular velocities, and torso left lateral bending angular velocity, and increased hip and knee flexion, regardless of box size. When lifting large boxes, belts significantly reduced torso right lateral bending and torso left twisting. No significant differential carryover effects were detected from belts. Conclusions. Subjects with belts lifted more slowly and used more of a squat-lift technique, regardless of box size. Belts reduced more torso motions while lifting large boxes.

Suspension Tolerance in a Full-Body Safety Harness, and a Prototype Harness Accessory

Workers wearing full-body safety harnesses are at risk for suspension trauma if they are not rescued in 5 to 30 min after a successfully arrested fall. Suspension trauma, which may be fatal, occurs when a persons legs are immobile in a vertical posture, leading to the pooling of blood in the legs, pelvis, and abdomen, and the reduction of return blood flow to the heart and brain. To measure suspension tolerance time, 22 men and 18 women with construction experience were suspended from the chest D-ring (CHEST) and back D-ring (BACK) of full-body, fall-arrest harnesses. Fifteen men and 13 women from the original group of subjects were then suspended using a newly developed National Institute for Occupational Safety and Health harness accessory (ACCESS), which supports the upper legs. Midthigh circumference changes were 1.4 and 1.9 cm, changes in minute ventilation were 1.2 and 1.5 L/min, changes in heart rate (HR) were 15.1 and 21.6 bpm, and changes in mean arterial pressure were 5.1 and −2.6 mmHg (p ≤ 0.05) for all subjects during CHEST and BACK, respectively. Kaplan-Meier median suspension time for all subjects for the CHEST condition was 29 min (range 4–60 min) and 31 min (range 5–56 min) for the BACK condition. The 95th percentile for suspension time was 7 min for CHEST and 11 min for BACK. Cox regression revealed that body weight had a statistically significant effect on the time until experiencing a medical end point (p ≤ 0.05) during the BACK condition. Mean (± SD) suspension time was 58 ± 6 min (range 39–60 min) for all subjects for the ACCESS condition. There were no terminations due to medical symptoms during the ACCESS suspension, changes in physiological variables were small, and 85% of ACCESS subjects completed 60-min suspensions. These data provide information on motionless suspension tolerance time to standards-setting organizations and demonstrate the potential of a prototype harness accessory to delay or prevent suspension trauma.

Improving Risk Assessment: Research Opportunities in Dose Response Modeling to Improve Risk Assessment

Substantial improvements in dose response modeling for risk assessment may result from recent and continuing advances in biological research, biochemical techniques, biostatistical/mathematical methods and computational power. This report provides a ranked set of recommendations for proposed research to advance the state of the art in dose response modeling. The report is the result of a meeting of invited workgroup participants charged with identifying five areas of research in dose response modeling that could be incorporated in a national agenda to improve risk assessment methods. Leading topics of emphasis are interindividual variability, injury risk assessment modeling, and procedures to incorporate distributional methods and mechanistic considerations into now-standard methods of deriving a reference dose (RfD), reference concentration (RfC), minimum risk level (MRL) or similar dose-response parameter estimates.

Frailty models of manufacturing effects.

The median service lifetime of respirator safety devices produced by different manufacturers is determined using frailty models to account for unobserved differences in manufacturing processes and raw materials. The gamma and positive stable frailty distributions are used to obtain survival distribution estimates when the baseline hazard is assumed to be Weibull. Frailty distributions are compared using laboratory test data of the failure times for 104 respirator cartridges produced by 10 different manufacturers tested with three different challenge agents. Likelihood ratio tests indicate that both frailty models provide a significant improvement over a Weibull model assuming independence. Results are compared to fixed effects approaches for analysis of this data.

Protection Factor for N95 Filtering Facepiece Respirators Exposed to Laboratory Aerosols Containing Different Concentrations of Nanoparticles

A previous study used a PortaCount Plus to measure the ratio of particle concentrations outside (C out) to inside (C in) of filtering facepiece respirators (FFRs) worn by test subjects and calculated the total inward leakage (TIL) (C in/C out) to evaluate the reproducibility of the TIL test method between two different National Institute for Occupational Safety and Health laboratories (Laboratories 1 and 2) at the Pittsburgh Campus. The purpose of this study is to utilize the originally obtained PortaCount C out/C in ratio as a measure of protection factor (PF) and evaluate the influence of particle distribution and filter efficiency. PFs were obtained for five N95 model FFRs worn by 35 subjects for three donnings (5 models × 35 subjects × 3 donnings) for a total of 525 tests in each laboratory. The geometric mean of PFs, geometric standard deviation (GSD), and the 5th percentile values for the five N95 FFR models were calculated for the two laboratories. Filter efficiency was obtained by measuring the penetration for four models (A, B, C, and D) against Laboratory 2 aerosol using two condensation particle counters. Particle size distribution, measured using a Scanning Mobility Particle Sizer, showed a mean count median diameter (CMD) of 82 nm in Laboratory 1 and 131 nm in Laboratory 2. The smaller CMD showed relatively higher concentration of nanoparticles in Laboratory 1 than in Laboratory 2. Results showed that the PFs and 5th percentile values for two models (B and E) were larger than other three models (A, C, and D) in both laboratories. The PFs and 5th percentile values of models B and E in Laboratory 1 with a count median diameter (CMD) of 82 nm were smaller than in Laboratory 2 with a CMD of 131 nm, indicating an association between particle size distribution and PF. The three lower efficiency models (A, C, and D) showed lower PF values than the higher efficiency model B showing the influence of filter efficiency on PF value. Overall, the data show that particle size distribution and filter efficiency influence the PFs and 5th percentile values. The PFs and 5th percentile values decreased with increasing nanoparticle concentration (from CMD of 131 to 82 nm) indicating lower PFs for aerosol distribution within nanoparticle size range (<100 nm). Further studies on the relationship between particle size distribution and PF are needed to better understand the respiratory protection against nanoparticles.

Modeling Frailty in Manufacturing Processes

The expected service life of respirator safety devices produced by different manufacturers is determined using frailty models to account for unobserved differences in manufacturing process and raw materials. The gamma and positive stable frailty distributions are used to obtain survival distribution estimates when the baseline hazard is assumed to be Weibull. Frailty distributions are compared using laboratory test data of the failure times for 104 respirator cartridges produced by 10 different manufacturers. Likelihood ratio tests results indicate that both frailty models provide a significant improvement over a Weibull model assuming independence. Results are compared to fixed effects approaches for analysis of this data.

Relative mortality for correlated lifetime data

Abstract Comparing correlated lifetimes for a group of individuals to a standard reference population may require variance adjustment of marginal model estimates or the use of conditional random effects models with shared frailty. We present the cumulative relative mortality, the marginal model robust variance estimator and the frailty models in estimating relative mortality for individuals who have correlated lifetimes due to group clustering. The positive stable and gamma frailty distributions are considered in the frailty models. The performances of both marginal and frailty models are compared using simulation. Applying these methods, we show siblings for centenarians had longer life spans than their US cohort reference population.

Occupational Injury Risk Assessment: Perspective and Introduction to the Second Special Issue

Risk assessment continues to be an important process for collecting and describing the evidence regarding the potential of exposure to a particular hazard to induce adverse responses. Workers often experience much higher exposures to hazards than the general population and thus are worthy of special attention. Injuries in the workplace are frequent and result in great impact to the lives of the workers affected. In addition, workplace injuries also impose high economic costs on industries with high exposures to hazards. During 1980 to 1997, there were an average of 16 work-related deaths per day (CDC 2001). A recent workshop “Future Research for Improving Risk Assessment Methods: Of Mice, Men, and Models” focused on Occupational Injury Risk Assessment as a high research priority (Zeise et al. 2001). This workshop was sponsored by the National Institute for Occupational Safety and Health, National Institute of Environmental Health Sciences, US Environmental Protection Agency, American Chemistry Council and United Auto Workers. Invited participants from a wide diversity of interests identified Occupational Injury Risk Assessment as the second highest priority, with general agreement that research on this topic has the potential to reduce deaths, disability and suffering from occupational injury. In this second special HERA issue devoted to Occupational Injury Risk Assessment, there is an emphasis on specific situations that demonstrate the success of risk assessment techniques to reduce occupational injuries. Several of the papers demonstrate the application of risk assessment methods to prevent injuries through maintaining safer workplaces and reducing individual injury risks. Other papers represent advances in methods of evaluating the level of risk in various industries and occupations or new paradigms for identification of risk. Some of the research