Main drain tests are required by section 9.7.5 of the 2000 edition of the Life Safety Code, which requires sprinklers systems to be tested and maintained according to NFPA 25 Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, 1998 edition. The purpose of a main drain test is covered in the Annex section A-9-2.6, of NFPA 25, which says:
“…(main) drains also are used to determine whether there is a major reduction in waterflow to the system, such as might be caused by major obstruction, a dropped gate, a valve that is almost fully closed, or a check valve clapper stuck to the valve seat. A large drop in the full flow pressure of the main drain (as compared to previous tests) normally is indicative of a dangerously reduced water supply caused by a valve in an almost fully closed position or other type of severe obstruction. After closing the drain, a slow return to normal static pressure is confirmation of the suspicion of a major obstruction in the waterway and should be considered sufficient reason to determine the cause of the variation. A satisfactory drain test (i.e., one that reflects the results of previous tests) does not necessarily indicate an unobstructed passage, nor does it prove that all valves in the upstream flow of water are fully opened. The performance of drain tests is not a substitute for a valve check on 100 percent of the fire protection valving.”
The Annex section A-9-2.6 also continues to describe what a main drain test is:
The main drain test is conducted in the following manner:
- Record the pressure indicated by the supply water gauge [Static Pressure]
- Close the alarm control valve on alarm valves
- Fully open the main drain valve
- After the flow has stabilized, record the residual (flowing) pressure indicated by the water supply gauge
- Close the main drain valve slowly
- Record the time taken for the supply water pressure to return to the original static (nonflowing) pressure
- Open the alarm control valve”
I find that many hospitals, especially the older hospitals, do not have the requisite pressure gauge, drain valve and a suitable drain to collect the substantial flow of water to properly conduct a main drain test. Also, I always recommend to my clients to shut off the fire pump and leave on the jockey pump during the main drain tests. Shutting off the fire pump for this test constitutes an impairment, and appropriate interim life safety measures must be considered, according to the organization’s policy.
Please be aware that a main drain test is required downstream of any control valve that has been closed, then opened. Also starting with the 2002 edition of NFPA 25, a single quarterly main drain test is required downstream of all backflow preventers in the system. This will be a requirement once the 2012 edition of the Life Safety Code is finally adopted.