Dry barrel hydrants must be tested annually to ensure proper drainage and operation. According to NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems:
After testing, full drainage of the hydrant must occur within 15 minutes. This ensures no residual water remains in the hydrant barrel, which could freeze in cold climates and damage the hydrant.
If the hydrant fails to drain within 15 minutes, it indicates an obstruction or malfunction in the drainage system that must be corrected.
10 minutes (A): Not enough time for standard drainage.
30 minutes (C) and 60 minutes (D): Exceed the acceptable limit defined by NFPA 25.
Reference:
NFPA 25, Section 7.3.2: Annual testing and drainage requirements for dry barrel hydrants.