2013-11-01 12:00 - Messages

Slip-related characterization of gait kinetics

Investigation of pervious concrete as a slip-resistant walking surface
Slip-related falls are a significant health problem, particularly on icy walking surfaces. Pervious concrete, a material allowing rapid exfiltration of melted ice from the walking surface, may help reduce slipping risk. Therefore, the purpose of this study was to compare slipping characteristics of traditional and pervious concrete walking surfaces in icy conditions using kinetic biomechanical analyses. We hypothesized that pervious concrete, in comparison to traditional concrete, would be characterized by less severe ice-related alteration of friction during gait. Healthy young participants performed gait trials on traditional and pervious concrete surfaces during dry and icy conditions. Ground reaction forces were used to determine maximal magnitude and timing of loading phase normal force, shear force, and normalized friction usage, defined as the ratio of shear to normal force normalized to static coefficient of friction. Pervious concrete, in comparison to traditional concrete, exhibited smaller ice-related increases in normalized friction usage. While ice-related delays in achieving peak friction were observed on traditional concrete, icy conditions did not have an impact on maximal shear force magnitude or timing on pervious concrete. Our results indicate a larger margin between friction forces used during walking and those that would cause a slip, suggesting that pervious concrete may be a more slip-resistant alternative to traditional concrete in icy conditions. The findings reported here may lead to pavement design recommendations for the use of pervious concrete in areas of high pedestrian traffic and elevated slipping risk.

Source : King, Gregory W., Bruetsch, Adam P., & Kevern, John T. (2013). Safety Science, 57, 52-59. 

Modeling acoustic propagation in a compartment fire

Firefighters unable to move and in need of rescue use an audible alarm to signal for help. Rescue teams can then follow this sound to the firefighter. This alarm is governed by NFPA 1982 : Standard on Personal Alert Safety System (PASS). Introduced in 1983, the PASS has saved many firefighter lives. However, a number of incidents have occurred where the PASS is less effective. There have been incidents where the PASS was heard sporadically on the fireground, or where localization of the alarm was difficult, leading to injury and loss of life. We hypothesized that the temperature field created by the fire is distorting the sound, making it difficult to recognize and localize. At ICA 2013, the authors presented experimental results showing changes in the room acoustic transfer function as the fire evolved. This paper will present efforts at modeling these effects. Using a combination of computational fluid dynamics and wave models, a comprehensive model will be presented capable of modeling sound propagation in the firefighting environment. The goal of this work is to develop a PASS signal more robust against distortion by the fire, and better able to serve the firefighting community.

Source : Abbasi MZ, Wilson PS, Ezekoye OA. J. Acoust. Soc. Am. 2013; 134(5): 4218.

The effect of firefighter personal protective equipment on auditory thresholds

Communication on a fire scene is essential to the safety of firefighters. Not only to be able to hear and understand radio chatter, but also alarm signals used on the fireground. One such alarm is the Personal Alert Safety System (PASS) device. This device is used to help locate a downed firefighter. One part of this complex problem is the effect of the protective equipment (helmet, eye protection, hood, coat) on hearing. Previous findings have shown the effect of this protective equipment on head related transfer functions using a KEMAR. [Suits et al. (2013, June). Paper presented at the International Congress on Acoustics, Montreal, Canada] The physical acoustic measurements showed a change in the signal that would reach the tympanic membrane. To relate the findings of the physical measurements to human reactions, the change in auditory threshold caused by wearing the personal protective equipment was measured. The changes seen in the physical acoustics measurements caused the auditory threshold of the subjects to increase at higher frequencies. The measured increases at 3000 Hz, 4000 Hz, and with an example PASS signal were between 5 and 10 dB.

Source : Suits JI, Champlin CA, Wilson PS, Ezekoye OA. J. Acoust. Soc. Am. 2013; 134(5): 4228.

The effect of a helmet on cognitive performance is, at worst, marginal

A controlled laboratory study
The present study looked at the effect of a helmet on cognitive performance under demanding conditions, so that small effects would become more detectible. Nineteen participants underwent 30 min of continuous visual vigilance, tracking, and auditory vigilance (VTT + AVT), while seated in a warm environment (27.2 (±0.6) °C, humidity 41 (±1)%, and 0.5 (±0.1) m s(-1) wind speed). The participants wore a helmet in one session and no helmet in the other, in random order. Comfort and temperature perception were measured at the end of each session. Helmet-wearing was associated with reduced comfort (p = 0.001) and increased temperature perception (p < 0.001), compared to not wearing a helmet. Just one out of nine cognitive parameters showed a significant effect of helmet-wearing (p = .032), disappearing in a post-hoc comparison. These results resolve previous disparate studies to suggest that, although helmets can be uncomfortable, any effect of wearing a helmet on cognitive performance is at worst marginal.

Source : Bogerd CP, Walker I, Brühwiler PA, Rossi RM. Appl. Ergon. 2013.

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