This study was conducted to investigate the occupational stress of the personnel of disaster and emergency medical management center 115 and the role of demographic variables in 2019. The results demonstrated that the highest and the lowest level of occupational stress was attributed to the "role" domain, followed by the "demand" and "changes" domain. In this regard, Hosseinzadeh et al. stated that the highest and the lowest occupational stress in emergency medical personnel were related to role and demand domain . Sharifi et al. stated that demand dimension allocated the highest occupational stress and role dimension allocated the lowest occupational stress among emergency medical personnel . Mei Lu et al. depicted that the subscale of problems related to time and workload based on the occupational stress questionnaire (which is consistent with the demand dimension of HSE questionnaire) were among the subscales that allocated the highest score among emergency medical nurses . However, Mahdizadeh et al. concluded in their study that issues related to workload do not create much stress in personnel employed in 115 .
As it is clear, the strongest and the weakest factor of occupational stress in various studies is very diverse and even contradictory and in fact, it is influenced by the characteristics of the research sample. The role domain measures the "right understanding of individuals from the organization". In this study, it reveals that individuals do not have sufficient awareness of their duties and responsibilities, the goals and perspectives of the organization and the expectations that the work place have from them and therefore (especially according to the young research sample) training and justifications upon arrival and in-service by senior executives to clarify the problem and reduce occupational stress is helpful. Also, another main cause of occupational stress in this study was the demand dimension specifying overwork, long hours, lack of rest and rapid working, so senior executives can take measures such as providing sufficient work force, compulsion to use paid leave and so on can reduce occupational stress of employees. On the other hand, the dimension of changes is related to the "way of organizing and changing the forces of the organization", so it seems that in the present study, there is a good relationship between managers and employees regarding inter-organizational changes.
The results showed that younger people had experienced more occupational stress (P=0.000). It should be noted that the sample population was young (more than half of the participants were in the age range of 20 to 30 years). Similarly, Moti et al. reported that as technicians' age increases to 40 to 45 years, their stress level is decreased . It is natural that as the age and work experience increases, occupational stress decreases, in fact, increasing age to a certain level can have a protective role against stressors. D'Ettorre et al. stated that age had a significant relationship with occupational stress of nurses in emergency medical department .
However, Seyed Javadi et al. found contrast results in their study; as age increased, occupational stress increased in personnel employed in 115 . Bardhan et al. considered age in relation with occupational stress, so that they announced that age over 40 is a risk factor for higher occupational stress among emergency medical nurses . The researchers justified the results of their research so that by increasing age, the power of compatibility of individuals and coping with stressful work conditions is decreased, and it is natural that the occupational stress to be increased. In the present study, an increase was observed in stress in the age range of more than 50 years.
Another perspective observed in the present study demonstrate that single status account for more occupational stress than married status (P=0.001). Similarly, Shareynia et al. reported that stress was higher among single nurses . However, the study by Seyed Javadi et al. showed that there is no relationship between occupational stress of emergency medical technicians and marital status . And, in contrast, Mahboubi et al. announced that married has more stress among emergency medical personnel . The results of recent research justify the fact that single status attributes higher expectations from the family and the workplace which increases hours and workload and thus result in increased occupational stress.
Educational level had a significant relationship with the level of occupational stress experienced by individuals (P=0.001). Only two percent of the participants in the study were postgraduate students who had experienced more occupational stress than others. Namdari et al. showed that as the level of education increased, the occupational stress of personnel employed in 115 increased and the tendency to continue service decreased which is in line with the present study . By increasing education level as knowledge and skill increased and the quality of service is expected to improve, because expectations from people are higher and often are assumed to be more in difficult situations as specialized work is performed; therefore, it implies that occupational stress is increased as knowledge and skills improve. Moti et al. in their study concluded that technicians with a bachelor's degree had experienced more occupational stress compared to other people (with a diploma and associate degree), which is consistent with the present study, but ultimately there was no significant relationship between educational level and stressors . People in stressful situations that require quick decision-making, regardless of their level of education, may not be able to act effectively and experience high stress.
There was a significant relationship between occupational stress and education degree (P=0.000). In this study, the majority of participants (80%) had emergency medical degree that had less stress compared to other fields of study (nursing, anesthesiology, and practical nurse). Similarly, Namdari et al. showed that occupational stress had a significant relationship with education field of emergency medical employees . This issue can be justified so that emergency medical graduates have passed academic specialized training for providing service in pre-hospital conditions, thus they experience less occupational stress compared to other courses trained for hospital conditions. This issue shows the need to employ more relevant people in emergency medical centers as compared to general skill employees or ttain them in emergency situation. It seems natural that selecting people with a job-related degree will reduce workplace stress.
Furthermore, the results of this study reflected that people in urban bases generally had more occupational stress compared to people in road bases (P=0.000). Similarly, Modi et al. and Namdari et al. stated that the stress in employees of urban base was higher than road base [10, 14]. In the present study, the number of missions per day, the type of missions, and other factors associated with the type of base of work has not been investigated. Therefore, in case of further studies and confirmation of the relationship between these factors and occupational stress, it is suggested the workplace base periodically to be changed to modify and control stress and to be paid special attention to the personnel of bases with more workload. However, the study by Seyed Javadi et al. showed no relationship between stress level and type of base . Leszczynski et al. stated that EMS employees experience varying degrees of stress in terms of work place. And in fact, there was a significant difference in the occupational stress of technicians working in emergency medical services and other services (earthy emergency medical services, emergency medical departments, etc.) and they had clearly experienced less stress . Similar results were obtained in other medical groups, and Yuwanich et al. showed that nurses in the emergency medical department were more exposed to occupational stress compared to nurses in other sections due to their higher workload . One general conclusion is that personnel experience different level of stress in different locations and departments.
By more investigation, it was specified that stress in employees of urban bases was more in the three dimensions of demand (P=0.018), control (P=0.000) and changes (P=0.038). Therefore, it can be concluded that the main cause of more occupational stress is stress and workload (demand dimension), lack of control of person over the work being done (control dimension) and lack of adaptation to changes within the organization (change dimension) in urban bases. In this regard, Shareynia et al. revealed that there was a significant difference between the nurses in emergency and non-emergency medical department in terms of sub-scale of workload (due to high number of referrals) which increased their occupational stress . Sharifi et al. stated that the dimensions of change, role, peer support, and responsible support had a significant relationship with the type of base of work .
The results showed that although the mean total score of occupational stress in people with experience less than 5 years and 21-30 years (both sides of the spectrum) was more than others, there was no significant relationship between work experience and occupational stress. Mati et al. reached quite similar results and stated that there was no relationship between work experience and occupational stress among emergency medical technicians, but in work experience of more than 20 years, the sum of scores of stressors was higher . Yuwanich et al.  stated that low experience and work experience are related to occupational stress of nurses in emergency medical services and Bardhan et al. similarly indicated that work experience less than 10 years is a strong risk factor of higher occupational stress in nurses, which is somewhat consistent with the present study . On the other hand, d'Ettorre et al. considered work experience related to occupational stress in burses of emergency medical services. Another study also showed that by increasing work experience of personnel employed in 115, occupational stress also increased. The researchers described the finding that by increasing work experience, the overall duration of employees' presence at work placed increased and encountered stressors more . Generally, it can be stated that occupational stress is present throughout the service of individuals, but it increases in amongst less experience and in the late stages of service.
Although it was expected occupational security to decrease the experience of stress but employees with more permanent employment (formal and contractual) had experienced high occupational stress, however, in the present study, a significant relationship was not observed between type of employment and the occupational stress. In this regard, some studies have shown that there is a significant relationship between employment status and occupational stress among technicians employed in 115 and nurses of emergency medical department [10, 28, 29].
There was a significant relationship between working hours of personnel and their occupational stress, and unexpectedly, the results showed that people with the lowest working hours (less than 150 hours per month) experienced more occupational stress compared to others. This finding may be justified by the fact that being away from the workplace will increase the stress at the time of presence. However, the results of Shareinia et al. showed that there is a mild positive relationship between overtime and occupational stress; i.e the more overtime, the stress is increased in emergency medical nurses . Another study showed that working hours per week was not related to occupational stress of employees employed in 115 .