# Field Measurements of Free Ascending Behavior of Occupants along Medium-Long Stairway
## 1 Introduction  
With the increasing number of the underground facilities, such as subways, underground road tunnels, underground commercial buildings, and underground comprehensive transportation hubs, in recent years, safety issues, especially fire safety issues, are becoming more and more important. In underground fires, high temperature and a large amount of smoke would be produced [1, 2, 3], and how to evacuate the occupants to the ground quickly and safely is the key point in the safety of the underground buildings [4, 5, 6].  
The stairway is an important element of evacuation in underground buildings. Fully understanding the ascending motion on stairs is important for improving the evacuation efficiency during emergency conditions. It can also help in accurately predicting the evacuation time and for the design of the evacuation facilities in underground buildings [7, 8]. However, in contrast to research on descending stair evacuation [9, 10, 11], ascending stair evacuation has received little research attention in the past few years [12, 13].  
Age, gender, personal motility, dimensions of stairs, and crowd density are the common factors that can affect the walking speed on stairs [7, 8, 11, 12, 13]. Ascending on stairs is quite different from horizontal walking and descending on stairs. The human energy consumption for climbing stairs is about ten to fifteen times the energy needed for walking the equivalent horizontal distance [14]. The evacuation behavior on a tall stairway will differ from a short stairway. Physical exhaustion is often observed in walking a long distance upstairs, so fatigue due to vertical ascent would have a significant impact on the ascending speed and evacuation efficiency when walking for a long distance on stairs [15, 16]. For ascending on a long stairway, the degree of fatigue is closely related to the ascent distance.  
The walking behavior along a medium-long stairway might also be different from that on a long stairway.  
The subway station is a typical underground space with dense crowds, and safe evacuation from this kind of space is challenging and deserves detailed study. From a field survey, as shown in Figure 1, the depth of most subway stations in Beijing is no more than 30 m or near 30 m.  
As the depth of most modern underground facilities is about 30 m, previous results of the walking behavior on short stairways or super long stairways might not be applicable. For reliable prediction of the evacuation efficiency from the underground levels, the walking behavior on a medium-long stairway with a height of about 30 m needs to be further studied. The effects of fatigue, gender, age, and travel distance on ascending behavior were investigated through field experiments in this paper. For ascending on long stairs, due to the different physical conditions of each person, the effects of the crowd density on the ascending speed only appear at the start of the stairway, and the free ascending behavior is the focus to study. The structure of the stair is almost the same in most underground buildings; therefore, the effect of the stair structure was also not included in this study. Use of handrails and tiredness feelings during the experiment were considered to analyze their effects on the ascending speed. The relationship between the ascending speed and the travel distance on stairs was investigated. The results are more reliable for predicting the evacuation time for modern underground facilities than only using a single mean ascent speed.