"Today's illustration identifies two problems with this upright sprinkler in an attic on a 1-inch riser nipple (also known as a 'sprig up'). This damage was discovered by another company on a service call after other portions of the sprinkler system froze and broke. The corrosion resulted from a leak between the sprinkler and pipe. Why wasn't this identified as part of the annual inspection required by the National Fire Protection Association (NFPA) 25, 'Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems?' NFPA 25 requires 'Sprinklers shall be inspected from the floor level annually. . . . Sprinklers installed in concealed spaces such as above suspended ceilings shall not require inspection.' The purpose of these inspections is to find and correct obvious deficiencies; in this case, the sprinkler above the ceiling could not have been observed from the floor."
Coffee Break Training - Fire Protection Series No. FP-2009-9
United States Fire Administration: http://www.usfa.fema.gov/