The Federal Bureau of Prisons offers a career service, and desires to attract to its ranks those interested in making federal law enforcement their life work.  Those who possess the qualifications and aptitudes for lines of work other than the position appointed, may have an opportunity to advance to the position of interest.  However, all employees are required and expected to demonstrate their suitability for prison work, in the position to which they are initially appointed, before they will be considered for promotion or advancement into other lines of work.  It must be emphasized that while it is the policy of the Federal Bureau of Prisons to fill vacancies from within the service, if at all possible, no positive assurance of advancement to a particular line, field or work can be given to employees, nor can the length of the waiting period for such an advancement be estimated.  Each employee is in competition with others similarly qualified.  Selections are made from the persons considered the best qualified, based on technical expertise as well as temperament, experience, and ability.