Jerry D. Ramsey

Effects of workplace thermal conditions on safe work behavior

Abstract The effect of workplace thermal conditions on worker safety has not previously been adequately investigated, due in part to the difficulty of defining a suitable safety performance measure. This report describes a study conducted in two industrial plants to determine if a correlation exists between the safety-related behavior of workers and workplace thermal conditions. Both heat exposure measurements and behavioral observations were taken over a 14-month period, for a total of over 17,000 observations. The results indicate that temperatures below and above those typically preferred by most people have a significantly detrimental effect on the safety-related behavior of workers. This is demonstrated by an index based on the ratio of observed unsafe behaviors to the total number of observed behaviors. The relationship between this index of unsafe behavior and the ambient temperature formed a U-shaped curve. The minimum unsafe behavior index occurred within the zone of preferred temperature (approximately 17°C to 23°C, WBGT). Other factors such as metabolic workload and time during the shift also had significant effects on worker safety-related behavior.

Task performance in heat: a review

A wide array of variable conditions, tasks, subject populations, etc., have been included in studies that have produced data on perceptual motor performance in the heat. This paper uses a methodology for comparing these studies, regardless of the inherent differences, which allows determination of whether thermal effects are dominant enough to persist through diverse combinations of variables. Approximately 160 individual studies of perceptual motor performance reported in the literature were summarized based on thermal level, duration of exposure and the type of task performed. Results indicated no dominant effect of duration of exposure to the heat and no dominant effect of thermal level on mental/cognitive tasks. For perceptual motor tasks other than very simple or mental tasks, an onset of performance decrement was noted in the 30-33 degrees C WBGT range of temperature. This temperature level is consistent with the Recommended Exposure Limits for work in the heat at low levels of metabolic heat.

Effects of age related sensory degradation on perception of floor slipperiness and associated slip parameters

A laboratory study was conducted to determine how sensory changes in elderly people affect subjective assessments of floor slipperiness, and associated friction demand characteristics and slip distance. To relate these parameters to actual slip and fall incidents, 30 subjects from two age groups (young and elderly) walked around a circular track on the slippery and non-slippery floor surfaces, while wearing a safety harness to prevent injury in case of a slip or fall. Prior to the walking experiment, the Sensory Organization Test was performed. During the experiment, subjective assessments of surface slipperiness of the floor were obtained prior to walking and after walking on the floor. Slip distance, required coefficient of friction (RCOF) and adjusted friction utilization (AFU) were assessed utilizing motion analysis and force platform systems. The results indicated that sensory changes in the elderly increased the likelihood of slips and falls more than their younger counterparts. This was due to incorrect perceptions of floor slipperiness, and uncompensated slip parameters such as slip distance and adjusted friction utilization.

Abbreviated guidelines for heat stress exposure.

A wide array of recommendations, rules and research results have been arregated into a simplified set of decision criteria for estimating threshold levels of heat stress. The WBGT is used as a basis, with appropriate modification for metabolic heat generated during work, velocity of air movement, state of acclimatization, amount of clothing (e.g., shorts, jackets, coats, enclosed suits), age, obesity, and sex. When WBGT levels for the person-task-environment combination are exceeded, initiation of appropriate engineering and work practices are indicated.

Recommended alert limits for perceptual motor loss in hot environments

Abstract Research concerning the effects of heat on task performance has been extensive and contradictory. This paper summarizes over a hundred and fifty studies where performance has been reported as a function of temperature, exposure time and type of task. It suggests that prediction of performance loss first requires categorizing the type of tasks since mental or very simple tasks typically show little decrement in the heat and are frequently enhanced during brief exposures. Other perceptual motor tasks collectively depict a pattern of onsett of performance decrement in the 30°C–33°C WBGT temperature range, and the decrement appears to be relatively independent of exposure time. This is the same temperature range as that associated with the onset of physiological heat stress for the worker performing sedentary or very light work. It appears that performance decrement may be better explained by body temperatures, as indicated by the head or blood temperature, than by the deep body temperature.

Heat Stress Limits for the Sedentary Worker

Performance on four sedentary tasks was monitored during temperatures of 85 degrees f, 95 degrees F, and 105 degrees F WBGT for work periods up to 2 hours. Results were compared with limits recommedned for occupational safety and health regulations. It is suggested that this limit is not a single line, but rather a range of temperture-time combinations. Further, mans compensating nature during short exposures supports a higher temperature limit for brief work bouts.

Heat stress indices: A review paper

This paper represents a review of the thermal indices commonly used for assessing heat stress conditions in an environment, e.g., Corrected Effective Temperature, New Effective Temperature, Heat Stress Index, Wet Bulb Globe Temperature and Wet Globe Temperature. The advantages and disadvantages of the indices are included, as well as an example of calculations and procedures required to determine the resulting values of each heat stress index. Separate sections for Programmed Hand Held Calculators, the Mean Equivalence Lines and the International Organization for Standardization (ISO) standards are also provided in the paper.

Ergonomic factors in task analysis for consumer product safety

This paper describes an approach and methodology for applying ergonomic factors in the resolution of questions concerning the design, manufacture and use of consumer products. An important set of principles to be considered in the safety of products relates to ergonomie factors, and these principles can be integrated into any program of product safety analysis and enhancement. This paper views this area as a total information system, and suggests applications for and systematic approaches to ergonomie analysis, including the performance of operations and task analyses.

Inherent variability in heat-stress decision rules

There currently exist many decision rules which help define hot working environ–ments through the use of heat threshold values, or onset points for increasing risk of heat strain. A degree o f variability is introduced into these decision rules due to the inherent need to estimate metabolic workload and to measure fluctuating thermal variables. This study evaluated the extent of this variability, and compares heat-stress decision rules based on comprehensive and abbreviated methodologies. The approach consisted of pairing Wet-Bulb Globe Temperature (WBGT) values with the corresponding values of human heat exchange calculated from the generally accepted equations developed as the Heat-Stress Index (HSI). Several levels of metabolic workload, clothing, radiant heat, wet-bulb temperature, air temperature and air velocity were used as input to a computer model for generating the corresponding HSI and WBGT. This iterative procedure provided the ability to look at the specific work, clothing and environmental c...

Monitoring performance as a function of work/rest schedule and thermal stress.

This study evaluates the effects of work/rest schedules as a means of retarding job fatigue and maintaining vigilance performance in hot climates. Six different work/rest schedules were investigated at three levels of heat stress (74°, 82°, and 90° effective temperature). Experimental sessions were 3 hours long for each of the 108 subjects used. Results show that the factors of temperature, work period, and work/rest ratio of the levels utilized in the study did not, by themselves, affect vigilance performance to a high degree. However., when high temperatures, long work periods, and short rest periods occurred in combination, a disproportionate decrement in monitoring performance was observed.