The FBI is near-impenetrable, with applicants intensely scrutinized and assessed over an extended period. To apply to become an FBI agent, one must be between the ages of 23 and 37. Due to the decision in Robert P. Isabella v. Department of State and Office of Personnel Management, 2008 M.S.P.B. 146, preference-eligible veterans may apply after age 37. In 2009, the Office of Personnel Management issued implementation guidance on the Isabella decision. The applicant must also hold American citizenship, be of high moral character, have a clean record, and hold at least a four-year bachelor's degree. At least three years of professional work experience prior to application is also required. All FBI employees require a Top Secret (TS) security clearance, and in many instances, employees need a TS/SCI (Top Secret/Sensitive Compartmented Information) clearance. To obtain a security clearance, all potential FBI personnel must pass a series of Single Scope Background Investigations (SSBI), which are conducted by the Office of Personnel Management. Special Agents candidates also have to pass a Physical Fitness Test (PFT), which includes a 300-meter run, one-minute sit-ups, maximum push-ups, and a 1.5-mile (2.4 km) run. Personnel must pass a polygraph test with questions including possible drug use. Applicants who fail polygraphs may not gain employment with the FBI.