Jul 07 2014

Main Drain Tests

Category: Main Drain,Questions and Answers,Sprinklers,TestingBKeyes @ 5:00 am

Q: Where are main drain tests required to be done? This is a large medical facility with nine story towers. Several fire mains feed the various campus buildings. Is the main drain test required to be done only where the fire mains supply the system risers, or does it also need to be done on each floor at the riser as well? Would you please supply your rationale for your answer?

A: According to the 2000 edition of the Life Safety Code, main drain tests are regulated by NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, 1998 edition. Section 1-5 of NFPA 25 defines a main drain as the primary drain connection on the system riser and also is utilized as a flow test connection. Section 9-2.6 requires a main drain test must be conducted annually at each water-based fire protection system riser to determine whether there has been a change in the condition of the water supply and control valves. NFPA 25 does not adequately define what a ‘system riser’ is, so we turn to the Handbook for NFPA 13 Standard for the Installation of Sprinkler Systems which identifies a ‘system riser’ as the above ground horizontal or vertical pipe between the water supply and the mains (cross or feed) that contains a control valve (either directly or within its supply pipe) and a waterflow alarm device. A system riser is more than just a subset of the term riser, which is broadly defined as any vertical piping within the sprinkler system. As indicated by the definition, a system riser can be any aboveground pipe in a vertical or horizontal orientation installed between the water supply and the system mains that contain specific devices. By this definition it appears one could loosely define the locations of a main drain test to be conducted wherever there is a control valve and waterflow alarm switch. In a large multi-story facility such as yours, that would most likely require a main drain test at least on every floor, possibly more. The Accreditation Organizations (AOs, such as Joint Commission, HFAP and DNV) typically do not seek this level of compliance. Most of the AOs only expect main drain tests to be conducted at the base of the risers of the sprinkler system, not at every floor. However, depending on your state agency surveyors who conduct CMS validation surveys, it is very reasonable and possible that they will expect the main drain tests to be conducted at every floor. To continue with additional information, the purpose of a main drain test is covered in the Annex section A-9-2.6, which says main drain tests are used to determine whether there is a major reduction in waterflow to the system, such as might be caused by a 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 a previous test) 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 main drain test is conducted in the following manner:

  1. Record the pressure indicated by the supply water gauge [Static Pressure]
  2. Close the alarm control valve on alarm valves
  3. Fully open the main drain valve
  4. After the flow has stabilized, record the residual (flowing) pressure indicated by the water supply gauge
  5. Close the main drain valve slowly
  6. Record the time taken for the supply water pressure to return to the original static (nonflowing) pressure
  7. Open the alarm control valve