## 1 Introduction  
On 11 March 2011, the Great East Japan Earthquake damaged the electric power supply lines to the Fukushima Daiichi Nuclear Power Station (NPS). The tsunami that followed caused substantial destruction of the safety infrastructure on the site and led to the loss of both off-site and on-site electrical power, which resulted in the loss of cooling functions at the reactors and the spent fuel pools. Large amounts of radioactive materials were released, and the problem of radioactive contamination has severely affected the lives of people and shocked many countries throughout the world. Units 1 to 4 of the Fukushima Daiichi NPS were damaged during the disaster, and all reactors were brought to cold shutdown on December 2011. Units 5 and 6 were permanently shut down on December 2013. On April 2014, the Fukushima Daiichi Decontamination & Decommissioning Engineering Company was formed by the Tokyo Electric Power Company (TEPCO), in partnership with Japanese Government and principle contractors, to perform the decommissioning of Fukushima Daiichi NPS.  
Decommissioning of Fukushima Daiichi NPS is challenging work that has never been done before, which presents industrial and chemical hazards as well as radiological ones, and indeed these hazards generally present high risk to workers [1]. At present, many TEPCO workers, nuclear reactors manufacturers, construction companies, and their contractors are engaged in the decommissioning project for the Fukushima Daiichi NPS and are consequently exposed to various health risks. At present,the Fukushima Daiichi NPS site is divided into three zones (see Figure 0(a)), and workers are instructed to wear proper Personal Protective Equipment (PPE) when working in different zones (as illustrated in Figure 0(b) [2]). The designated zones (and the associated PPE) are listed below.  
1. G Zone: general work uniforms are required, e.g., disposable dust masks.
2. Y Zone: coveralls are required, e.g., full-face dust masks or half-face masks.
3. R Zone: anorak and full-face masks are required.  
on-site safety regulations due to all kinds of reasons, even if they have been previously educated and trained. Moreover, even though the signs and partitions mark the R zone and Y zone areas in the Fukushima Daiichi site, intrusions into these areas may occur within only a few minutes of carelessness. In addition, TEPCO has contracted various tasks to more than 20 companies (primary contractors), each of which, in turn, outsources some of its tasks to multiple layers of subcontractors. This complex structure could hinder consistent enforcement of on-site regulatory rules [3]. Traditional on-site occupational safety monitoring is usually carried out by on-site/off-site observers and relies heavily on the \"human eye\", which is not sufficient to protect workers because of human factors and human errors (e.g., errors and unintentional mistakes, poor judgment and bad decision-making, and disregard for procedures). Thus, an automated monitoring approach is highly desirable in performing the safety monitoring of decommissioning workers to ensure PPEs are appropriately used in different zones.  
This paper proposes a vision-based approach to automatically identify the proper use of PPE in response to the limitations of the safety monitoring systems at the decommissioning sites. The current goal of this work is to detect the hard hats and full-face masks in each image captured by surveillance camera and to identify whether the individuals on the decommissioning sites are wearing PPE properly. This paper will describe how an image of an individual's posture is characterized using OpenPose [4] to extract a body's keypoints. Then, the location of a hard hat and full-face mask is determined using the YOLOv3 model [5]. Finally, the geometric relationship between the PPE and the body are analyzed to determine whether the PPE is used appropriately.