Human Behaviour

Human behaviour in the fire refers to the actions, decisions, and responses of individuals or groups of people in situations involving fires. It encompasses how humans interact with fire, respond to fire-related emergencies, and influence fire occurrences and consequences through their actions. The prediction of human behaviour during a fire emergency is one of the most challenging areas of fire protection engineering. Yet, understanding and considering human factors is essential to designing effective evacuation systems, ensuring safety during a fire and related emergency events, and accurately reconstructing a fire. Below are some factors necessary for considering human behavior in fire.

a.    Population Numbers and Density

b.    Alone Or with Others

c.     Familiarity with the Building

d.    Distribution and Activities

e.    Alertness

f.      Physical and Cognitive Ability

g.    Social Affiliation

h.    Gender

i.       Age

All above mentioned factors effects the human behaviours in fire. For example: When people are in bed or asleep, their response times to a fire alarm can be expected to be considerably delayed (Alertness). Frequent users of a building may have a complete knowledge of the nearest and alternative egress routes and warning systems compared to non-familiar occupant which effects the evacuation process (Familiarity with the Building). The number of people using a building or space and their distribution or density in that space will affect evacuation travel speeds (Population Numbers and Density).

Human Response to fire Cues and Alarms

When considering human behaviour in fire, there is an assumption made that building occupants respond immediately to initial cues of a fire. This assumption would be incorrect, in many cases, it would provide inaccurate results from egress calculations. Instead, there is considerable evidence in the literature to the contrary and taking that evidence into account when assessing a building’s design would likely improve the life safety afforded its building occupants.

The Protective Action Decision Model (PADM), which is based on over 50 years of empirical studies of hazards and disasters provides a framework that describes the information flow and decision-making that influences an individual to take protective actions in response to natural and technological disasters. The process can occur individually or, more likely, within a group. The PADM can be adapted for use in building fires.

Moving further, understanding the actions that occupants take during the building fire emergency timeline. The timeline begins with ignition of the fire, encompasses the pre-evacuation period, and ends with the movement period. The pre-evacuation period is the time between receipt of fire cues by a member (or members) of the building population and a decision to take protective action. The pre-evacuation time also includes the time during which protective actions are performed, including preparatory actions (e.g., gathering personal items, getting dressed), actions to protect others (e.g., warning others, assisting), and actions to protect oneself. Below diagram shows building fire emergency timeline, that displays an example building notification type (i.e., fire alarm).

ASET is generally calculated by fire models, based on design fire scenarios. RSET is generally calculated by egress models and movement calculations. The occupant behavioral scenarios described above are used to configure the approaches used to quantify RSET as well as to develop occupant movement strategies. Time egress analysis is used to calculate RSET and there are two approaches available to do this analysis:

1.    Algebraic equation-based methods

2.    Computer-based models

In this article our focus will be on Algebraic equation-based analysis for calculating required evacuation time (RSET).

EGRESS TIME ANALYSIS BY ALGEBRAIC EQUATION-BASED METHODS

There are two versions of the methods involving the application of algebraic equations: simplified method and component by component analysis. The simplified version requires that a controlling element in the egress system be identified. A controlling element is one where the greatest normalized flow is expected (the normalized flow is defined as the flow rate along a path divided by a characteristic width for the path as described later in this section). The simplified version consists of three calculations: (1) time to reach controlling element, (2) time to travel through controlling element, and (3) time to travel from controlling element to outdoors (or place of safety). This method assumes that all occupants start their evacuation simultaneously. In cases with high-rise buildings, the exterior stairwell door is often the controlling element, in which case the estimated evacuation time, t, is determined as

These three time periods listed are determined by adopting a hydraulic analogy to assess the flows associated with evacuating building occupants. In this respect, the movement of occupants is described in terms of velocities and flow rates. The velocity is defined as expected (i.e., the distance travelled by the occupant per unit time1). The flow rate is defined as the number of persons per unit time who pass a particular point in the egress component (e.g., the number of persons per minute who pass through a doorway). One other useful parameter is termed the specific flow. The specific flow is the flow rate normalized by the effective width of the egress component.

Below table is used to find k factor:

Density:

Density has significant influence on walking speed. As such it is an important parameter in evacuation studies. Density of moving groups are typically between 1 per/m2 to 2 per/m2. However, a wide range of densities are feasible. Minimum density would be associated with situations where only one individual is located in a large egress component. Conversely, a maximum density is associated with crowd flows where individuals are virtually in contact with one another.

Specific Flow:

The flow rate of occupants along a particular egress path has been found to be linearly proportional to the portion of the width of the path that people use. The portion of the path that individuals actually use is referred to as the effective width. This parameter was initially identified by Pauls (1980).

Specific flow versus Density graph shows highest specific flow occurs at 1.88 per/m2 (0.175 per/ft2).

Below Figure depicts the effective width as compared to the clear width, which is the term typically used in building code analyses of the adequacy of the means of egress components. The effective width is generally is smaller than the clear width because small portion of the egress component is often unoccupied by individuals as they want to maintain some distance from wall or handrails suited at the edge of the egress. Below figure is for illustration.

Below chart is developed on experimental basis to find out thickness of boundary layer for different egress components.

Flow:

Flow of the occupant is product of specific flow and effective width. The flow rate parameter may be used in a simplified method for determining the egress time in buildings. Flow rates are also used to determine if queues form and the amount of time for dissipating queues. Queues form whenever the flow rate approaching a particular point in the egress system exceeds the maximum flow rate possible from that point. This is relevant where two egress paths merge (e.g., two corridors, or in stair- wells where people entering a stairwell merge with those travelling in the stairwell from other floor levels). Queues dissipate whenever the flow rate leaving the front of the queue exceeds the flow rate into the back of the queue.

Example: