Using Theory in Qualitative Research

I am doing a qualitative research (see purpose of research below) concerning stress and firefighters, can someone help me with the role of theory in my qualitative research plan and any considerations regarding this theory.

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Stress: Firefighters
The fire-fighters that were present at the World Trade Centre in New York during 9-11 illustrated the type of women and men entering into this profession - fit, brave, mentally strong, skilled, healthy, well-trained, and disciplined. The job set the firefighters faced was daunting - terrorists attack was pervading New York City endangering thousands of individuals trapped inside burning skyscrapers and buildings. Chaos and danger were everywhere. Many people were fleeing for their lives; however, fire-fighters were running straight to the danger. Fire fighters face extreme danger in their work environment. Many times if the fire is not controlled, it has the capacity to quite easily consume everything in its path - including the firefighters. Consequently, firefighters in many instances may face stress similar to soldiers going into a battle - the individuals may have adequate training, but one cannot accounts always account for the many variables that are ever present; thus, producing various levels of stress. Therefore, being a firefighter can be a profession that is very stress-inducing, numbering second to being a soldier as the "most stressful job in the United States" (Meyer, Zimering, Daly, Knight, Jeffrey, Kamholz, Gulliver, 2011). Just how stressful is the firefighting profession?
Purpose Statement
The purpose of this qualitative research is to study the stress that firefighters are faced with because of their profession. What are the specific stresses? Are these stresses job-related? How do the firefighters cope with their stresses? What are the measures that can be selected to help? It is the intent of this study to focus on the subject of stress by examining the available research as well as through actual interaction with the fire-fighters.

Research Questions
The research will focus on central questions such as whether being a fire-fighter is stressful. Why is this the case? What are the reasons contributing to the stress? Is it the firefighters' personality or the nature of the job? Is stress of the job higher in others and less in some? How do they cope and manage?
Questions
This particular research concerning fire fighters and the experiencing of stress was chosen because firefighting can be a very stressful job, and although there may be considerable levels of stress, there is various way fire-fighters can/do manage and cope with it. The experience of being a fire-fighter of course is subjective, the levels of stress differing between individuals. But they all face danger and going into burning buildings entails bravado and extreme confidence in one's training, skillset and in the skillset and commitment of their fellow fire-fighters. Can the fact be proven that firefighting is a stressful profession? It would seem that by following the qualitative perspective, one will be able to find answers.
My target population is my local firefighting unit due to the fact that I know most of them which would allow for a much easier aspect for interviews. Knowing the local unit is an advantage in gaining more information; however, by my knowing them, I will be able to interview each individual fire-fighter. With a good set of information from interviews, it is possible to identify their shared stresses and to put together measures that can be of help in alleviating the effects of stress for the local fire fighters.