# On-Demand Maintenance Method Using Fault Prediction to Reduce Elevator Entrapment
## 2 Fault Cause Analysis  
By the end of 2023, the total number of operational elevators in City H had reached 211,432, meaning a 10.81% year-on-year increase, and this ranks as the city second among all provincial capitals in China in elevator number. Among these elevators, 46,000 had been working for over 10 years, of which 12,000 had exceeded 15 years of operation.  
The historical elevator fault data was collected from the records of City H's Elevator Emergency Response Center (96333). In 2023 alone, the city's elevator emergency response platform received 30,865 calls related to elevator malfunctions and entrapment rescues and conducted 19,930 emergency interventions. The completed entrapment incident data were subsequently analyzed, and the overview is shown in Figure 1 and Table 1.  
According to the statistical data of fault categories, the three leading causes of elevator stranding faults are door system faults (26.34%), human-caused faults (22.84%), and externally caused faults (12.13%).  
Among all recorded faults, door system malfunctions accounted for 5250 incidents, representing the leading cause of elevator entrapments. These faults primarily resulted from equipment aging, improper operation, and inadequate maintenance. The specific fault manifestations are shown in Table 2.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fault Category** & **Cause of Fault** & **Number of Faults** & **Percentage of Faults** \\ \hline \multirow{6}{*}{Door systems} & Car door lock fault/Landing door lock fault & 1235 & 6.20\% \\  & Door operator malfunction & 870 & 4.37\% \\  & Non-compliant clearance between the door & 421 & 2.11\% \\  & knife and roller & 421 & 2.11\% \\  & Safety edges/light curtains protection & 166 & 0.83\% \\  & device fault & 166 & 0.83\% \\  & Interlock fault between the active and passive & 174 & 0.87\% \\  & door leaves & 174 & 0.87\% \\  & Door contact switch fault & 544 & 2.73\% \\  & Door hanger wheel damage & 303 & 1.52\% \\  & Door guiding system fault & 155 & 0.78\% \\  & Others & 1382 & 6.93\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Overview of door system faults.  
Figure 1: Historical fault analysis: (**a**) category share; (**b**) share of equipment causes.  
As shown in Table 3, a total of 4553 human-caused faults were mainly triggered by uncivilized elevator behaviors, among which the more common phenomena included blocking the doors with domestic or renovative garbage, deforming the doors due to barbaric handling of heavy loads, delaying the door from closing, etc.  
Externally induced entrapments totaled 2417 cases, primarily triggered by environmental factors including power outages, extreme summer heat, and typhoon-associated rainstorms. Specific fault manifestations included sudden pauses of elevator operation, short-circuiting of electrical components due to water ingression, the triggering of protection mechanisms by the elevator control system, etc., as shown in Table 4. Therefore, when carrying out elevator fault prediction, it is necessary to consider the variations in the real operating environment parameters to obtain more accurate results.  
In summary, door system faults stand as the most prevalent category among all elevator fault types. As a critical subsystem, door-related malfunctions may directly or indirectly lead to entrapment incidents, establishing them as the primary challenge requiring urgent resolution in contemporary elevator maintenance and safety management.