# Building Fire Evacuation: An IoT-Aided Perspective in the 5G Era
## 4 Preliminary Design of an IoT-Aided Building Fire Evacuation Control System
### Information Sources and Data Transmission
#### 4.2.2 People Counting  
To obtain the occupant count and localization information inside buildings, various occupant counting techniques can be employed. The mainly used technologies are radio frequency (RF), infrared, video cameras, or network connecting signals such as GPS, cellular data, wireless local area network (WLAN), and Bluetooth [62]. The benefits and drawbacks of these approaches were reviewed by [PERSON] et al. [62]. In order to cause minimal influence on occupants' normal lives and privacy, multiple applicable techniques are applied to count occupants in building fire evacuation control. First, a turning gate and swipe card system can be used at the building entrances to count the total entering and leaving occupants. The data count can be directly sent to the local server and connected to the IoT platform with a wired connection. Since the turn gate system only allows the authorized occupants to gain entry, manual recording should be kept for additional visitor entry. The building manager can record visitors' information with a web-based spreadsheet through the Wi-Fi network in buildings. Additionally, it is considered that a turn gate system may not be suitable for people counting in residential or commercial buildings, which much affects occupants' normal life, and it hardly tells the specific number of occupants on each floor. Therefore, it is suggested to use visual-based video counters in these areas. The visual-based video counter is a video camera combined with computer vision-based algorithms to count people [63]. It can be used by direct mounting above the building/floor entrances and conducting the counting. This approach causes minimal influence on building occupants and has high recognition accuracy. Due to the high bandwidth and high reliability needs for streaming video data transmission, it is better to use wired connections for local data transmission. By connecting with the existing backbone cable of the building, the real-time local video can be directly sent to the local server and connected to the IoT service platform. An alternative approach is to link these visual-based video counters to a gateway (placed elsewhere) with cables and then connect to the IoT service platform with broadband cellular networks. The connectivity in this way not only makes it easier for the service platform to be placed on the cloud but also can ensure the reliability of streaming video data transmission in local fire environments. For the broadband cellular networks, 4G LTE and the latest 5G NR can be employed. However, it is worth noting that people counting using visual-based video counters may fail when the building floor is full of smoke, so a thermal counter can be used at the exits of each floor as an alternative option in case the thick smoke obscures the visual-based video counters. The thermal counter is a low-resolution infrared camera combined with the people counting algorithm to enable the counting of people in low light conditions [45]. In practical usage, the thermal counter can be put inside a protective box to isolate it from the effects of fire temperature and smoke. For the data transmission of the thermal imaging data of the thermal counter, wired connections to the service platform of this IoT system are better applied. Finally, occupant counting needs to be carried out at the room level. For corridors and public areas in buildings, the visual-based approach is applicable. However, the visual-based approach seems inappropriate for individual rooms and private use areas because privacy protection is the major concern in these places. As a result, it is recommended to use infrared beam counters. The infrared beam counter mainly consists of Passive InfraRed (PIR) sensors and their communication modules. The PIR sensors can detect general movement by identifying infrared radiation emitted by or reflected from occupants without collecting any other personal information. They have been widely used in occupancy counting in buildings [64; 65; 66; 67].