It depends on whether your scanner meets the standards set by NARA Preservation Programs. Scanners with printing functions/capability are not allowed in the textual research rooms.
Once approved, the supervisor and staff may designate an area for you to work.
Approval is good only for that research room. Because the records in each research room present unique formats and preservation issues, you must receive separate approval to use the scanner in another research room.
Information regarding equipment allowed in National Archives research rooms can be found at: http://www.archives.gov/research/start/whats-allowed.html
Rules for using scanners in National Archives research rooms and descriptions of allowable scanners are at: http://www.archives.gov/research/order/scanning.html