## 1 Introduction  
This paper presents the results of research focused on the assessment of design specifics of protective equipment, which is implemented at the Faculty of Safety Engineering, University of Zilina, with the support of other departments. The subject of the research is mainly the testing of protective equipment used by the units of the integrated rescue system and civil protection units of the population. The research focuses on the objective characteristics of protective equipment but also on the characteristics that are perceived by its users. It is therefore a subjective assessment, similar to the study focused on protective clothing [1]. Here, attention has been given to the establishment of test criteria for the purpose of subjective evaluation as part of an overall assessment of the quality of protective anti-chemical and anti-gas clothing [1, 2]. This paper builds on the authors' research activity and focuses on the testing of protective gas masks with an emphasis on subjective evaluation. Subjective evaluation is particularly important in the area of decision-making on the choice of an appropriate protective measure. The objective characteristics of the protective equipment predetermine the area, the environment, and the use of the protective equipment. However, once these characteristics have been determined, the views of the users of the protective equipment must also be taken into account [1]. Subjective evaluation and monitoring of users' opinions have been the subject of several studies worldwide. A Finnish study focused on the subjective perception of the wearer of insulating protective clothing. Testing has highlighted the impact of protective clothing on the workload and performance of wearers of the clothing, which absolutely must be taken into account [3]. [PERSON] et al. [4] point out in their study the importance of subjective opinions and insights of personal protective equipment users. Their aim was to identify appropriate test methods to investigate the impact of personal protective equipment on the mobility of firefighters. The findings provide guidance for the development of improved and comfortable protective equipment [4]. [PERSON] et al. [5] have addressed testing of the effect of a protective gas mask on the physiological functions of its wearers. Specifically, they performed four measurements on a sample of respondents. These measurements were conducted without the gas mask and with the gas protective mask at rest and during exercise. The authors focused on measuring exertion index, breathing patterns, and gas exchange. The study demonstrated increased physiological stress on the respondents both at rest and during exertion. Thus, the protective gas mask affects the respiratory stress described by its wearers. The data obtained can be used to inform retrofitting and modification of protective mask designs. However, the authors did not address other technical characteristics, such as visibility in a protective mask or sufficient fit. The evaluations also did not include the views of its users [5]. The tightness of the protective gas mask in relation to the respondent's face type and the prevalence of stubble in respondents has been the subject of research by [PERSON] [6]. The author's testing was able to confirm the assumption that the unshaven face of the rescuer may have a negative impact on his health in relation to the weaker tightness of the face shield mask. The author also tested the possibility of using a filter-ventilation unit instead of a protective filter [6]. In their study, [PERSON] and [PERSON] [7] addressed the design of a new prototype protective filter for gas masks. The measurement results confirmed its functionality and the reduction of inhalation resistance [7]. [PERSON] et al. [8] addressed testing of gas protection masks with respect to their suitability during first aid administration. Using a simulation of patient intubation, they tested the suitability of the protective mask, focusing on the fit of the filter.