Jay P. Mehta

Evaluating the physical demands on firefighters using track-type stair descent devices to evacuate mobility-limited occupants from high-rise buildings

The physical demands on firefighting personnel were investigated when using different types of track-type stair descent devices designed for the emergency evacuation of high rise buildings as a function of staircase width and evacuation urgency. Twelve firefighters used five track-type stair descent devices during simulated urgent and non-urgent evacuations. The devices were evaluated under two staircase width conditions (1.12, and 1.32 m), and three devices were also evaluated under a narrower staircase condition (0.91 m). Dependent measures included electromyographic (EMG) data, spine motion, heart rates, Borg Scale ratings, task durations and descent velocities. Stair descent speeds favored the devices that had shorter fore/aft dimensions when moving through the landing. EMG results indicated that there were tradeoffs due to design features, particularly on the landings where the physical demands tended to be greater. On the landings, devices that could be rolled on four wheels reduced the deltoid and bicep activation levels.

Physiological and biomechanical responses to a prolonged repetitive asymmetric lifting activity.

This study investigated the effects of a prolonged repetitive asymmetric lifting task on behavioural adaptations during repetitive lifting activity, measures of tissue oxygenation and spine kinematics. Seventeen volunteers repeatedly lifted a box, normalised to 15% of the participants maximum lifting strength, at the rate of 10 lifts/min for a period of 60 min. The lifts originated in front of the participants at ankle level and terminated on their left side at waist level. Overall, perceived workload increased during the repetitive lifting task. Erector spinae oxygenation levels, assessed using near-infrared spectroscopy, decreased significantly over time. Behavioural changes observed during the repetitive lifting task included increases in the amount of forward bending, the extension velocity and the lateral bending velocity, and a reduced lateral bending moment on the spine. These changes, with the exception of the reduced lateral bending moment, are associated with increased risk of low back disorder. Practitioner Summary: Repetitive lifting is known to affect low back injury risk; however, the biomechanical mechanisms linking physical fatigue and back injury risk are not well understood. This study showed that behavioural adaptations made by people performing asymmetric repetitive lifting activity may increase risk through increased dynamic loading of the tissues.

A biomechanical and subjective assessment and comparison of three ambulance cot design configurations

Effects of ambulance cot design features (handle design and leg folding mechanism) were evaluated. Experienced ambulance workers performed tasks simulating loading and unloading a cot to and from an ambulance, and a cot raising task. Muscle activity, ratings of perceived exertion, and performance style were significantly affected by cot condition (p < 0.05). Erector Spinae activity was significantly less when using Cot-2s stretcher-style handles. Shoulder muscle activity was significantly less when using Cot-2s loop handle. During loading and unloading, operators allowed the cot to support its own weight most often with Cot-2s stretcher-style handles. Preference for Cot-2 (either handles) over Cot-1 (with loop handle) was consistent across tasks. Handle effects were influenced by operator stature; taller participants received more benefit from Cot-2s stretcher-style handles; shoulder muscles’ demands were greater for shorter participants due to handle location. Providing handle options and automatic leg folding/unfolding operation can reduce cot operators effort and physical strain. Practitioner Summary: Paramedics frequently incur musculoskeletal injuries associated with patient-handling tasks. A controlled experiment was conducted to assess effects of ambulance cot design features on physical stress of operators, as seen through muscle activity and operators perceptions. Differences between cots were found, signalling that intentional design can reduce operators physical stress.

Comparisons of tibial accelerations when walking on a wood composite vs. a concrete mezzanine surface

Mezzanine surfaces can be made from concrete, bar grate, or composite materials. Anecdotal data indicate that mezzanines in distribution centers made from composite materials, due to their increased compliance, may be a more comfortable working surface. Prior research suggested that a measure of tibial shock, peak tibial acceleration, could potentially discriminate the biomechanical differences between these surfaces. The objective of this study was to quantify differences in tibial accelerations as 27 people walked on mezzanines constructed from concrete and a wood composite material. Accelerometers were attached bilaterally to the shins of volunteers, and data were collected as they walked 30.5 m on each surface at their normal walking speed, a faster-than-normal walking speed, and a slower-than-normal walking speed. Peak acceleration values obtained from the leg with the highest values were compared. On average, the peak acceleration values were 5% higher on the concrete mezzanine as compared with the wood composite mezzanine (p = .036). These findings suggest that individuals working on mezzanines in distribution centers constructed from composite surfaces would potentially experience less discomfort associated with long exposure periods on these surfaces.

Ergonomic Evaluation of Track-Type Stair Descent Devices Used for the Evacuation of High Rise Buildings

INTRODUCTION Fire service personnel are often the first people called upon when evacuating large multi-story buildings during emergency and non-emergency conditions. During such evacuations, firefighters may need to transport building occupants with physical disabilities down several flights of stairs. While several stair descent devices or “evacuation chairs” are currently on the market for emergency evacuation of individuals with motor disabilities from high rise buildings, there is little empirical data indicating their impact on the physical demands placed on the firefighter. The purpose of this investigation was to evaluate five existing evacuation chairs with track systems, each representing a different design approach, that have been developed to transport individuals who are ill or who have ambulatory disabilities down multiple flights of stairs.

Exploring the Effects of Seated Whole Body Vibration Exposure on Repetitive Asymmetric Lifting Tasks

This study investigated changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after exposure to whole body vibrations. Seventeen healthy volunteers repeatedly lifted a box (15% of lifters capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/min for a period of 60 minutes. Prior to lifting, participants were seated on a vibrating platform for 60 minutes; in one of the two sessions the platform did not vibrate. Overall, the physiological responses assessed using near-infrared spectroscopy signals for the erector spinae muscles decreased significantly over time during the seating and the lifting tasks (p < 0.001). During repetitive asymmetric lifting, behavioral changes included increases in peak forward bending motion, twisting movement, and three-dimensional movement velocities of the spine. The lateral bending movement of the spine and the duration of each lift decreased significantly over the 60 minutes of repetitive lifting. With exposure to whole body vibration, participants twisted farther (p = 0.046) and twisted faster (p = 0.025). These behavioral changes would suggest an increase in back injury risk when repetitive lifting tasks are preceded by whole body vibration exposure.

Effects of Transfer Distance on Spine Kinematics for De-palletizing Tasks

One approach to reducing lateral bending and twisting in manual lifting tasks is to separate the lifts origin and destination, thereby encouraging lifters to step and turn their entire bodies. The objective of the current study was to determine how the degree to which one laterally bends and twists changes with transfer distance and initial lift height. Eighteen males lifted 10.9 kg boxes from a conveyor 0.5 m, 0.9 m, and 1.3 m above the floor and placed the boxes on a conveyor .50, .75, 1.00, 1.25, 1.50, or 1.75 m away at a height of .9 m. During picking, lateral bending and trunk extension velocities increased with increasing transfer distances. When placing the box, the degree of twisting decreased with increased transfer distance. In sum, when attempting to control the twisting and lateral bending during de-palletizing, the lift origin and destination should be separated by between 1 and 1.25 meters.

The effects of transfer distance on spine kinematics when placing boxes at different heights

Twisting and lateral bending motions in repetitive lifting tasks are associated with occupational low back injuries and can be challenging to reduce with engineering controls. This study tested the hypothesis that twisting and lateral bending can be reduced by changing the transfer distance. Eighteen males, with no material handling experience lifted 10.9 kg boxes from 0.9 m above the floor and placed the boxes at a destination located 0.50, 0.75, 1.00, 1.25, 1.50, or 1.75 m away and at heights of 0.5 m, 0.9 m, and 1.3 m above the floor. Overall, twisting and forward bending decreased with increased transfer distance when placing the box. Conversely, the lateral bending when lifting and placing the box increased with increasing transfer distance. In short, having a transfer distance between 1 and 1.25 m when performing palletizing tasks to different heights may optimally balance spine kinematics, back injury risk, and productivity measures.

Effects of Task Precision Demands on Behavioral and Physiological Changes During a Repetitive Asymmetric Lifting Activity

Objective: This study investigated the effects of task precision demands on behavioral and physiological changes during repetitive asymmetric lifting. Background: Repetitive lifting encountered in manual material handling leads to muscle fatigue and is a documented risk factor for low back disorder. Method: A total of 17 healthy volunteers performed repetitive asymmetric lifting for 60 min (10 lifts/min). Task precision demands were imposed by varying the entry width onto the destination conveyor. Physiological changes were assessed using near-infrared spectroscopy obtained from the erector spinae muscles. Three-dimensional spine kinematics and moment responses were quantified to understand behavioral changes during the lifting activity. Results: Task precision demands showed no effect on erector spinae muscle oxygenation levels. Behavioral changes associated with repetitive lifting included increases in the overall lift duration, peak forward bending motion, and three-dimensional movement velocities of the spine, along with a decrease in the lateral bending moment. Relative to low precision demands, high precision demands resulted in 20% longer placement periods, which, in turn, resulted in a 12% increase in the time-integrated twisting postures and a 10% increase in the time-integrated lateral bending moments during load placement. Conclusion: The elevated risk of low back injury when lifting under greater precision demands is likely due to the sustained spine twisting and the sustained lateral bending moment on the spine in the final phase of these lifts. Application: Understanding behavioral changes to repetitive asymmetric lifting, especially for tasks requiring greater precision can be used to support injury prevention efforts.

Comparisons of Tibial Shock when walking on four different flooring surface materials used in distribution centers

Flooring surfaces can be made from concrete, bar grate, composite materials, or may be covered with matting material. Anecdotal data suggested that surfaces made from wood composite materials may be a more comfortable surface on which to work. The objective of this study was to quantify differences in tibial shock as 16 people walked on concrete, bar grate, a wood composite material, and a concrete surface covered with matting. An accelerometer was attached to the right shin of volunteers who were asked to walk on each surface. Significant differences across the four surfaces were observed when each participant walked at their normal walking speed (p=.041) and when they walked at a faster than normal pace (p=.023). These findings suggest that individuals working in distribution centers, where extensive walking is part of the job, would possibly experience less lower extremity discomfort on selected floor surfaces.