# A BIM-Based Smart System for Fire Evacuation
## 2 Materials and Methods
### Fire Evacuation System Operation Mechanism  
The building's spatial layout and information are vital for a fire evacuation system. The minimum Level of Development (LOD) provided for the BIM Model is LOD 300, which presents the building components' geometry, material properties, and equipment [35; 41]. The smart sensors will be integrated into the BIM model. Data will be stored in the database connected to Dynamo, so data could be visualized and analyzed in real time using the BIM model. After data analysis, the system will identify the fire location, category, and severity and prevent false detection. Whenever the system scans and extrapolates the fire's characteristics, evacuation paths will be generated using the fire simulation and evacuation modules' history. Several fire sources and locations are simulated to create an FDS database. The tenability boundaries, including visibility, temperature, CO concentration, and smoke density, should be checked to validate the scenarios, as shown in Table 1.  
Visibility is considered a significant cause of human injuries and fatalities during building fires. In the initial fire phase, smoke is released due to blazing. Smoke comprises many toxic gases and small particles, which could smother or poison the stuck personnel. Particles in the smoke decrease humans' visibility, which leads to difficulty in escaping from the building. Smoke will become thicker with time and due to the fire's growth. Therefore, the visibility limit should be considered because the evacuation route could no longer be visible. The critical smoke height (Hc) is calculated based on Equation (1) [33]. \[\mathrm{Hc}=\mathrm{Hp}+0.1\;\mathrm{Hb} \tag{1}\]  
Hp is the typical height of eyes taken equal to 0.8 of human height, and Hb corresponds to the floor height. The FRI Research Institute states that the relation between visibility and smoke density could be computed using Equation (2) [42]:  
\[\mathrm{S}=\frac{\mathrm{K}}{\mathrm{e}} \tag{2}\]  
S is the visibility in meters, K is the proportionality constant that depends on the illumination of the evacuation sign, and e is the extinction coefficient (1/m). To start being emotionally affected by smoke, a value of e = 0.1(1/m) is enough, and to start showing strong emotional fluctuation, a range of e [0.35-0.55] is considered [38]. However, it should be noted that during fire hazards, occupants are affected psychologically by fear. Therefore, a value of e = 0.15 (1/m) is considered as the maximum allowable density during evacuation. On the other hand, this value considers the tenants unfamiliar with \begin{table}
\begin{tabular}{c c} \hline \hline
**Tenability** & **Tenability Boundaries** \\ \hline Smoke Density & \textgreater{}85\% \\ \hline Visibility & 13 m \\ \hline Temperature & 60 \({}^{\circ}\)C \\ \hline Air Intoxication: CO & 2500 ppm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Tenability boundaries for ASET calculation. the building's architecture, which constitutes the worst-case scenario. For e = 0.15, the visibility limit S for unfamiliar occupants is 13 m. For a familiar resident, e can be taken as 0.5, which gives a visibility limit S = 4 [43]. Humans will have visibility and mobility difficulties when the smoke density exceeds 85% [44]. 2. Temperature  
High temperatures can cause heatstroke, burns, and respiratory issues. The heat produced will start to impact the human body once (1) its upper layer radiation strength exceeds 180 \({}^{\circ}\)C and (2) the smoke layer of direct contact with the human body exceeds 60 \({}^{\circ}\)C [45]. 3. Gas intoxication  
Gases that affect occupants are CO, CO\({}_{2}\), and hydrogen cyanide (HcN). CO is considered the primary toxic gas during a fire [46]. The CO toxicity concentration harms humans when it exceeds 2500 ppm [47]. The FDS data are exported to Pathfinder to simulate the evacuation paths. According to [PERSON] et al. (2014) [48], Pathfinder is considered a reliable ABS tool to simulate evacuation.