# An Accident Model with Considering Physical Processes for Indoor Environment Safety
## 4 Application of STPA
### Results  
As discussed in Section 2.2, weather anomalies affect indoor environment, e.g., the heatwave of summer 2018. Thus, we consider the example of the high-temperature results in heat stroke [31; 32]. Heat stroke is clinically diagnosed as a severe elevation in body temperature (a core body temperature of 40\({}^{\circ}\)C or higher) that occurs in the presence of central nervous system dysfunction and a history of environmental heat exposure or vigorous physical exertion. It can be classified into nonexertional (classic) heat stroke and exertional heat stroke. The former occurs in very young or older people, or those with chronic illness when the environmental temperature is high. The latter happens to young fit people and involves prolonged excessive activities like sports. This paper focuses on the former case. Heat stroke can be assessed by heat stress indices, among which the most widely accepted and used one is the wet bulb globe temperature (WBGT) [33]. The Ministry of the Environment of Japan (Ministry of the Environment, Japan: [[http://www.wbgt.env.go.jp/en/](http://www.wbgt.env.go.jp/en/)]([http://www.wbgt.env.go.jp/en/](http://www.wbgt.env.go.jp/en/))) has recommended a criterion for thermal conditions based on the WBGT as shown in Table 2.  
We applied the tailored STPA to a Performers System that is for indoor temperature adjustment for thermal comfort. The structure of the system consists of four parts, i.e., home, home gateway, service intermediary, and service provider [12], as shown in Figure 6. The home is the place that occupants live in, which is equipped with different kinds of items, e.g., home appliances, to meet everyday living requirements. The home gateway is the gateway of the networked Performers to the outside world of the home. The indoor temperature adjustment service is executed here to issue commands for the control of Performers. The service intermediary aggregates various services from different service providers and maintains them locally. It can also respond to service subscriptions from home gateways. The service provider designs, publishes, and updates concrete services to the service intermediary for future use. We applied STPA to investigate the Behaviors of the Performers System to elicit possible Defects under related operation scenarios. Thus, we focus on executing the indoor temperature adjustment service in the home gateway to adjust the indoor temperature. The home gateway, service intermediary, and service provider can be taken as the smart home system core. \begin{table}
\begin{tabular}{l l} \hline \hline
**WBGT (\({}^{\circ}\)C)** & **Threat Level** \\ \hline \(\sim\)21 & Almost Safe \\
21\(\sim\)25 & Caution \\
25\(\sim\)28 & Warning \\
28\(\sim\)31 & Severe Warning \\
31\(\sim\) & Danger \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Recommended criteria for thermal conditions. Figure 6: The structure of the Performers System. In order to apply STPA, an assisting tool, i.e., STAMP Workbench (the STAMP Workbench is an open-source, free, easy-to-use tool for people who are interested in system safety analysis by using the STAMP/STPA. It was developed by the IT Knowledge Center of Information-Technology Promotion Agency, Japan. [[https://www.ipa.go.jp/english/sec/complex_systems/stamp.html](https://www.ipa.go.jp/english/sec/complex_systems/stamp.html)]([https://www.ipa.go.jp/english/sec/complex_systems/stamp.html](https://www.ipa.go.jp/english/sec/complex_systems/stamp.html))) is adopted for the analysis. The STAMP Workbench is claimed to include features such as concentration on thinking and help analysis and is not just an editing tool, or guide analysis procedure, but an unlimited and intuitive operation. Analytical results can be exported into Excel files and images.