Health care workers are at high risk of exposure to infectious diseases throughout their daily work. The use of personal protective equipment by health care workers is one of the most crucial measures to protect them against diseases. In this regard, the World Health Organization (WHO) and the Center for Disease Control and Prevention (CDC) proposed the N95 respirator masks in order to prevent the spread of infection through the air (1, 2) . The N95 respirator masks are compressed facial masks, so that they should be fixed on the face to provide respiratory protection (3) . A significant concern in the use of these masks is their reliability to impede the contaminant transport to an individual's breathing tract. This depends upon the degree of adaptation and appropriateness of the respirator mask for the mask wearer (4) . Although ergonomic aspects of using masks and the relationship between respiratory masks, human beings, and environment (5) . However, taking the principles of ergonomics into account to design a device is of paramount importance and can be considered as a critical factor affecting its success (6) . Knowledge of ergonomics can be used for designing, constructing, and selecting a device through measuring its compliance with the user.
Given that the respirators protect human beings; it is necessary to put more emphasis on ergonomic aspects of the respirator masks.
Over the recent decades, a lot of studies have been carried out to determine the limitations of the respirators with respects to Human Factors (HF) and to resolve them.
Several studies conducted on respirator masks in the field of the ergonomics have mainly focused on the respirator's fit, their comfort, their impact on the performance of individuals wearing them, and the mood of an individual while using the respirators.
To improve the respiratory masks user satisfaction, researchers have seeked to eliminate the respirators' poor face-mask compliance. Three features of the masks, which are closely related to the extent of compliance, include: respirator size, respirator shape and respirator edges. The face-mask compliance is also related with the size, shape and roughness of an individuals' face (7) .
According to a study conducted by Grinshpun et al., seal between face and respirator is the most important part responsible for any leakage of contaminants (8) . Following the issue of respirator fit, the respirator comfort was the most significant point considered by many researchers. In this regard, poor fit and discomfort were the most common reasons cited for not wearing a mask (7) .
Comfort should be an important selection criterion because when a person is comfortable using a respirator, he would probably wear it more accurately. Respirator masks may impose physiological stress on mask wearers.
Comfort of the respirator masks is usually determined based on a combination of physical and physiological factors (9) . It can be measured objectively or subjectively. The fourth issue associated with the respirator masks in the field of ergonomics is an individual's mental state while wearing masks. Its impact on a person's psychological mood or anxiety is a vital factor to evaluate and approve a new respirator mask (11) . During the recent years, there has been an increasing interest by the designers to introduce research methods in the field of ergonomics in order to assess and translate the respirator masks from a human perspective.
Since no study has been conducted to provide a complete evaluation of ergonomic aspects of a half-face respirator and checklists and questionnaires are the most convenient and common methods being used to investigate the ergonomic aspects of these devices, the present study aimed to introduce designers and users the N95 Respirators a novel questionnaire to ergonomically assess respirators among health care staff as an effective 
This study was a descriptive-analytic study. In this study, the content validity, Cronbach's alpha coefficient and test-retest methods were used to evaluate the validity, internal consistency and reliability of the designed questionnaire "N95 Respirator Masks Ergonomic Analysis among Medical Staff". Confirmatory factor analysis was used to assess its consistency and internal consistency (construct validity). The following procedures were adopted:
The first step was to determine the questionnaire content domain. The content validity of the N95 Respirator Masks Ergonomic Analysis among medical staff was specified after reviewing previous studies obtained from scientific resources in the field of the respirator masks ergonomics (7, 9) . The ergonomic aspects of the N95 Consequently, some items covering these dimensions of the N95 respirator mask for health care personnel were designed.
The questionnaire consists of four major dimensions: respirator fit, comfort, their impact on the performance of individuals wearing them, and the mood of an individual while using the respirators (13) . There were also some items included to gather information about the respondent's demographic information, awareness, received training, attitudes, and the frequency of wearing masks in order to further identify and specify the audience.
Then, Masih Daneshvari Hospital was selected as research setting since it is the national center for TB patients and its personnel are at high risk. Thus, the researchers personally attended in the research setting for several sessions and developed the items with regard to the above mentioned criteria. The first draft of the questionnaire was prepared, which contained 50 five-point Likert scale questions.
At this stage, the panel members were identified. To make an accurate judgment, the panel members were selected from experts active in the field of the questionnaire content domain. In some studies, the minimum number of panel members is suggested to be four persons (14, 15) . In this study, eight experts participated in the validation process to achieve greater consensus with high level of confidence. Eight experts were selected and the researchers met them in person.
Members of content validity were experts in ergonomics, occupational medicine and Occupational Health Engineering.
The first step to determine validity is to specify the face validity since if a change is required, no problem occurs for the entire questionnaire (16) . At this stage, the panel members' comments were applied and the researchers attempted to make the question wordings clear, fluent and appropriate.
In order to determine the questionnaire content validity, the questionnaires were submitted to the panel members once again and they asked to select one of three options (namely necessary, useful but not necessary, and not necessary) for each item. They were also asked to provide further comments on items considered as necessary or not necessary.
In order to determine the content validity, the panel members' comments being assigned based on necessity were quantified using the Content Validity Ratio (CVR).
Given the number of panel members (n=8) who participated in the validation process, the minimum CVR 
Content Validity Index (CVI) CVI is equal to the CVR mean of valid items. It represents integrity of judgments about the validity or enforceability of the final tool.
The term reliability generally refers to the consistency of a measurement specified by a tool at same conditions (18, 19) . Reliability coefficient ranges from zero to one.
Reliability coefficients of zero and one represent lack of consistency and perfect reliability, respectively (20) (21) (22) . At this point, 290 questionnaires were completed by the Masih Daneshvari Hospital medical staff. Then, the questionnaire internal consistency was determined using Cronbach's alpha coefficient.
In order to test the questionnaire reproducibility, the questionnaire was resubmitted after two weeks to 45 individuals who had previously completed the questionnaires to examine the questionnaire reproducibility using test-retest method and intra-class correlation coefficient index.
After investigating the internal consistency of the questionnaire items, confirmatory factor analysis was used to assess the relationship between variables and identify the factors (23). In the primary model, the goodness of fit values was not at an acceptable level. A better model was obtained after removing and mitigating items whose impact was not significant or had standardized coefficients less than 0.5. In this model, all indices were highly satisfactory and all conditions of internal consistency or convergent construct validity were observed for all components (Table 2) . Finally, a 45-item questionnaire containing five dimensions of awareness and training, comfort, performance, mood and fit was prepared.
Given that the correct choice of respiratory protective equipment regardless of the specifications and limitations of the users reduces their efficiency and can lead to irreparable damages to medical staff and hospital infection control system, the "N95 Respirator Masks Ergonomic Analysis among Medical Staff Inventory" can present a full assessment of ergonomic aspects of a half-face respirator (24, 25) . It not only can help the mask designers to increase the quality of the product but also can be used by the respiratory protection program executors at the hospital in order to enable them to select the correct type of respirator.
It can of great contribution in monitoring this program (26, 27) . The questionnaire contained 42 items and it is beneficial to use it in the health care system to evaluate the ergonomic problems of the masks and to have optimal choice in this respect and it can be used in the promotion of the staffs' behavior in wearing these masks when necessary.