# An Accident Model with Considering Physical Processes for Indoor Environment Safety
## 6 Related Work
### Accident Models  
The systems approach is considered as the dominant paradigm in safety research [34]. It views accidents as the unexpected interactions among system components, i.e., technical, social, and human elements. Among various systemic models, there are three most cited models [10], that is, STAMP [2], Functional Resonance Analysis Method (FRAM) [3], and Accimap [35,36].  
The concept of STAMP has been briefly introduced in Section 3.1. According to [10], over half of the reviewed papers were STAMP-related, which indicates a pervasive acknowledgement of its underlying rationale. Its application has attracted researchers from a broad field. The authors of [6] adopted it to investigate aircraft rapid decompression events. The authors of [4] applied it in the analysis of deepwater well control safety. In the field of railway, the authors of [5] investigated railway accidents and accident spreading by taking the China Jiaoji railway accident as the example. It has also been applied to the field related to poisonous or dangerous substances. The authors of [7] adopted it in analyzing the China Donghuang oil transportation pipeline leakage and explosion accident. The authors of [8] applied it to the Fukushima Daiichi nuclear disaster and to promote safety of nuclear power plants. Smart home systems are generally not considered as safety-critical systems. However, as weather anomalies, e.g., heatwaves, occur regularly due to global warming, smart home systems for indoor environment adjustment, in this context, can be taken as safety-critical. Thus, the STAMP model can be adopted for understanding accident formation in the home environment.  
FRAM was developed to act as both an accident analysis and risk assessment tool [10]. The FRAM model graphically describes systems as interrelated subsystems and functions that will exhibit varying degrees of performance varation. Accidents result from the fact that the emergent variation produced from the performance variability of any system component to \"resonate\" with that of the rest of the elements is too high to control. It has been discussed that the FRAM and STAMP approaches focus better on qualitative modeling and description of systemic behavior and accidents [37]. FRAM also has applications in different fields, e.g., the authors of [38] applied it to railway traffic supervision to investigate interdisciplinary safety analysis of complex sociotechnological systems. The authors of [39] extended FRAM by including a framework with steps to support hazard analysis. Some efforts have been tried to quantify it, e.g., the authors of [40] developed a semiquantitative FRAM based on a Monte Carlo simulation.  
The Accimap method is a graphical representation of a particular accident scenario that relates to systemwide failures, decisions, and actions [3; 36]. Accimap is a generic approach and does not use taxonomies (that is different than that of the STPA [2; 9]) of failures across the different levels of considered [41]. The Accimap produces less reliable accident analysis results compared to STAMP [42].  
The selection of accident analysis techniques depends on the system characteristics, i.e., manageability and coupling [1]. The systemic approaches are usually adopted by systems with low manageability and tight coupling. Systemic approaches related to complex sociotechnical systems have their own strengths. For one such system, it is better to adopt multiple approaches which supplement each other, even though STAMP is considered much more effective and reliable in understanding accidents and hazard analysis [10; 41; 42].