Experimental Study On Evacuation Of Individuals And Small Groups Considering Visibility Conditions

Real crowd is composed of a large proportion of small social groups and isolated individuals.The existence of small groups could be an obstacle during crowd evacuation,or may also improve the decision-making ability of crowd in emergency.There is no acknowledgeable statement whether small group behavior can reduce or improve the evacuation efficiency.Current evacuation experiments or model studies are mostly conducted under normal visibility conditions and lack consideration of small group behaviors in crowd.Low visibility in fire not only slows down evacuation,but also changes evacuees' behavior.Therefore,it is of significance to study crowd movement mechanism and typical evacuation behaviors under multi-effects of individual-group-crowd-environment,by conducting evacuation experiments of individuals and small groups under different visibility,so as to understand the characteristics of small groups and enrich the research of pedestrian evacuation dynamics.Based on individual and crowd evacuation experiments under different visibility conditions,as well as questionnaires,evacuation performance of individuals and small groups are systematically studied in this paper,including evacuation time,movement speed,route selection,psychological characteristics,typical evacuation behavior,etc.The main research works and conclusions are shown as follows:(1)Horizontal and vertical movement speed of individuals and three-person groups under four visibility conditions are obtained by conducting evacuation experiments in a multi-storey building.The route choices of evacuees under normal and low visibility conditions are analyzed.(2)Based on crowd evacuation experiments in a room,the relationship between pre-movement time/travel time and location/visibility condition is analyzed.The rule of movement speed changing with visibility is studied.It is found that the evacuated person vs.time curve develops from linear growth to ladder growth with reduced visibility.The evacuation process transforms from smooth to intermittent.(3)By comparing evacuation time and movement speed of individuals and small groupsunder different visibility conditions,it is found that small groups have an advantage over individuals during low-visibility evacuation.Although the pre-movement process of small group is slower than that of individual,small group evacuates faster than individual at low visibility.Small group behavior is helpful to stragglers,which is accordingly advantageous to overall evacuation.(4)Typical behaviors of pedestrians during evacuation are analyzed from experimental video.1)Leadership behavior: small group with leader usually moves with "vertical" structure,where leader stands at the first of structure.Leaders under evacuation condition are mostly come from leaders in normal walking condition,while the newly formed leaders during evacuation are someone who firstly recognize the correct evacuation information.2)Small group behavior: small groups in normal walking condition tend to maintain small group forms in emergency evacuation.3)Following behavior: following behavior in low visibility is conducive to crowd evacuation.4)Other typical evacuation behaviors such as surpassing behavior,comity behavior and helping behavior are also found during evacuation.(5)According to 97 valid questionnaires,majority of pedestrians(84%)are walking in groups on campus.Group size of two,three and larger than three occupies 57%,21% and6% respectively.Pedestrians within groups do not have physical touch in normal condition but the case becomes opposite in low visibility evacuation condition.Females in groups are more likely to have physical contact than males.