## 2 Literature Review
### Previous Research Related to PPE Planning  
Effective PPE protects work crews from hazards and exposure to risks on site [11]. It is critical to improve safety management effectiveness by selecting the appropriate PPEtype. To reduce the safety risk level, scholars have conducted a number of PPE evaluation studies, which can be divided into two aspects: type classification and type evaluation.  
For PPE type classification, different PPEs are adopted for various body parts of labor crews. For example, helmets are the traditional and frequently used type of PPE, providing head protection against engrossment and the shock of blows. Without suitable helmets, workers may slip or fall due to unconsciousness. Ear protection can protect workers from contact with noise, which effectively protects ears and reduces the risk of hearing loss. Eye protection protects workers from eye exposure to hazardous materials and the environment. Furthermore, respiratory protection measures can effectively protect labor crews from harmful dust, fog, gas, smoke, and vapors, which significantly reduces the risk of occupational diseases and health problems [12]. Arm and hand protection equipment is related to safety gloves, which play a vital role in protecting workers' arms and hands from electrical shock and chemical materials [13]. Although PPE cannot eliminate all the hazards on the jobsite, it is useful for reducing the potential accident effect [14]. As the types of PPE become more diverse, the decision-making risk associated with labor crews increases significantly. Therefore, a suitable type of PPE should be selected to solve serious accidents and health issues, such as falls and being struck by moving objects on the jobsite [15].  
Based on the classification of PPE types, type selection and evaluation methods are developed to analyze the performance of different PPE systems. [PERSON] and [PERSON] [16] developed a wholesaler selection model for PPE selection using integer linear programming and the Analytical Hierarchy Process (AHP) method to improve safety performance. [PERSON] et al. [17] reviewed the current research on smart PPEs, compared the traditional PPE types with high-tech PPEs, and analyzed the performance of the integration of innovative technologies and PPE. Based on the IoT system, [PERSON] et al. [18] developed an automated checking system for PPE-tool pairing to ensure that all the necessary PPE was properly worn by workers on the jobsite. [PERSON] et al. [2] conducted a conceptual model evaluation and analyzed the importance of adopting proper PPE in construction projects. This research further identified the causes of safety accidents and injuries, involving the negligence of construction workers, high-level work, unsafe facilities, and poor management. [PERSON] et al. [19] investigated the use of PPE, assessed its utilization and determinants among workers in construction projects in Uganda, and further summarized the factors that may lead to a low use of PPE among construction workers, such as lack of general knowledge of health and safety information, inadequate safety training, and employment of incompetent workers. [PERSON] and [PERSON] [14] investigated the cause of construction accidents through surveys and found that the improper use of PPE and an unwillingness to wear PPE were the major causes that led to accidents. In order to improve the effectiveness of PPE, it is suggested that the selection of suitable PPE types based on the relevant activities and providing workers with proper safety training are critical at construction sites.