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- Delin, Mattias, et al.
(författare)
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Ascending stair evacuation : walking speed as a function of height
- 2017
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Ingår i: Fire and Materials. - : Wiley. - 0308-0501 .- 1099-1018. ; 41:5, s. 514-534
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Tidskriftsartikel (refereegranskat)abstract
- There is reason to believe that factors such as physical exertion and behavioural changes will influence the ascending walking speed and ultimately the possibility of satisfactory evacuation. To study these effects, a 2-year research project was initiated with the focus on effects of physical exertion on walking speeds, physiological performance and behaviours during long ascending evacuations. Two sets of experiments on human performance during ascending long stairs, with a height of 48 and 109 m, were performed. The results include aspects such as walking speeds, physical exertion (oxygen consumption, heart rates and electromyography data), perceived exertion and behavioural changes, showing that physical work capacity affects walking speeds in case of long ascending evacuation and should be considered while using long ascending evacuation. Analysis of both walking and vertical speeds is recommended because it provides additional insights on the impact of stair configuration on vertical displacement and the importance of not using the same value for walking speed for different stairs because the design of the stairs has an impact. The novel datasets presented in this paper are deemed to provide useful information for fire safety engineers both for assisting fire safety design as well as the calibration of evacuation modelling tools.
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| 4. |
- Halder, Amitava
(författare)
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Evaluation of physical work capacity and leg muscle fatigue during exhaustive stair ascending evacuation
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractPhysical exhaustion can constrain human ascending work capacity and performance during emergency evacuation on stairs. The overall aim of this research was to explore and compare stair ascending capacities and physiological limitations during two different strategies: self-preferred pace in three different public stairways in the field, and controlled pace in a laboratory on a stair machine. Subjects of different ages, genders and body sizes were recruited from social media to simulate evacuation scenarios. The specific objective was to determine, through the combined analysis of oxygen uptake (VO2) and electromyography (EMG), whether local muscle fatigue (LMF) in the legs due to repetitive activity rather than cardiorespiratory capacity is the factor that limits ascending capacity.The average relative VO2highest reached 39-41 mL·kg-1·min-1 in the field tests, and 44 mL·kg-1·min-1 in the laboratory at 90% VO2max step rate (SR) L3. In the field tests, the VO2 and heart rate (HR) reached 89 to 95% and 89 to 96%, respectively, of the human capacity reported in literature. In the lab, the average %VO2max and %HRmax reached 94 and 97%, respectively. At the self-preferred pace, an ascent could be continued at a SR about 92-95 steps·min-1 on the stairs; while in the controlled pace ascent, the maximum duration could be sustained for about 2-6 minutes at 90% VO2max related to average SR 109 steps·min-1 on the stair machine. The EMG amplitudes (AMPs) were different in the two the ascending strategies, while neither of the VO2 uptake patterns were affected. During self-preferred ascent, the leg muscle AMPs showed a decreasing trend and median frequencies (MDFs) were unchanged or small decrease. In controlled ascent, the AMPs tended to increase and MDFs to decrease. The significant AMP decrease and the unchanged MDF in self-preferred ascent indicated reductions of muscle power production and possible fatigue compensation by reduction of speeds, which allowed subjects to continue their ascents until the end. In contrast, the significant increase of AMP and MDF decrease in the controlled pace were evidence of leg LMF. In order to interpret dynamic muscle activity changes over time, we developed the muscle activity interpretation squares (MAIS) to plot the muscle activity rate change (MARC) percentile points. In the self-preferred pace, the muscle fatigue recovery through power decrease and pace reduction was reflected in the MARC percentile points that appeared in the MAIS. In the controlled pace ascent, the MARC points were in the muscle fatigue square. Thus, MARC and MAIS are found to be useful to observe muscle activity changes during dynamic tasks. High and constant intensity (97% of HRmax) ascents were evidenced by hyperventilation and LMF due to insufficient recovery that forced the subjects to stop the ascents before 5-min. During 90% VO2max, LMF presumably prevented the VO2 from reaching VO2max and limited the ascent duration to 4.32 minutes. The results infer that leg LMF combined with cardiorespiratory capacity constrain the stair ascending capacities while any recovery can extend the tolerance.
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| 5. |
- Halder, Amitava, et al.
(författare)
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Limitations of oxygen uptake and leg muscle activity during ascending evacuation in stairways
- 2017
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Ingår i: Applied Ergonomics. - : Elsevier BV. - 0003-6870. ; 66, s. 52-63
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Tidskriftsartikel (refereegranskat)abstract
- Stair ascending performance is critical during evacuation from buildings and underground infrastructures. Healthy subjects performed self-paced ascent in three settings: 13 floor building, 31 floor building, 33 m stationary subway escalator. To investigate leg muscle and cardiorespiratory capacities and how they constrain performance, oxygen uptake (VO2), heart rate (HR) and ascending speed were measured in all three; electromyography (EMG) in the first two. The VO2 and HR ranged from 89-96 % of the maximum capacity reported in the literature. The average highest VO2 and HR ranged from 39-41 mL·kg-1·min-1 and 162-174 b·min-1, respectively. The subjects were able to sustain their initial preferred maximum pace for a short duration, while the average step rate was 92-95 steps·min-1. In average, VO2 reached relatively stable values at ≈37 mL·kg-1·min-1. EMG amplitudes decreased significantly and frequencies were unchanged. Speed reductions indicate that climbing capacity declined in the process of fatigue development. In the two buildings, the reduction of muscle power allowed the subjects to extend their tolerance and complete ascents in the 48 m and 109 m high stairways in 2.9 and 7.8 minutes, respectively. Muscle activity interpretation squares were developed and proved advantageous to observe fatigue and recovery over time.
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