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NFPA 25 Obstruction Investigation
In order for sprinkler systems to be effective for fire control and extinguishment, internal piping and sprinkler heads must be free from obstructions such as scale, silt, other foreign organic and/or inorganic material.
Chapter 13 of NFPA 25, 2002 Edition outlines requirements for obstruction investigations which include “minimum requirements for conducting investigations of fire protection system piping for possible sources of materials that can cause pipe blockage.” Review of Chapter 13 uses terminology reflecting three categories as they relate to obstruction investigation and prevention programs: 1) internal piping examinations, 2) obstruction investigations, and 3) flushing procedures.
An investigation of piping and branch line conditions (internal piping examination) is required to be performed every five (5) years in accordance with Section 13.2.1. This was a new requirement in the 2002 Edition of NFPA 25 and is mandatory for all sprinkler systems, including wet systems. The internal piping examination requires the opening of a flushing connection at the end of one (1) main and the removal of a sprinkler toward the end of one (1) branch line. The purpose of this requirement is to check for presence of Microbiologically Influenced Corrosion (MIC). Any tubercules or slime, if found, is required to be tested for the presence of MIC.
Although possible with wet pipe sprinkler systems, internal piping obstructions are more likely in dry and pre-action sprinkler systems and systems supplied by a fire pump drawing off an open pond or reservoir. An obstruction investigation is triggered by Section 13.2.2 if one of fourteen (14) conditions outlined in the standard exist, including identification of pin-hole leaks, plugged sprinklers, and foreign material observed in water during drain tests or plugging of inspectors test connections, to name a few.
Obstruction investigations are more labor intensive and thorough than the internal piping examination required by Section 13.2.1. Obstruction investigations require the internal examination of the system valve, riser, cross main and a branch line. Hoses are attached to several carefully selected cross mains and branch lines with burlap bags attached to the hose end. Water is flowed through the sprinkler system and out the hoses with any foreign material that may be present in the system piping collected in the burlap bags. If the obstruction investigation reveals less than ½ cup of scale washed from cross main(s), scale fragments not large enough to plug sprinklers, or full unobstructed flows are obtained from the branch line(s), the system can be considered reasonably free from obstructions.
If this is not the case, and the sprinkler system is found to be obstructed a flushing procedure is mandated by Section 13.2.4. Flushing procedures must be performed by qualified personnel and requires a thorough flushing of the entire system beginning with the yard mains, then the sprinkler riser(s), feed main(s), cross main(s), and branch line(s).
Flushing procedures can be performed using the hydraulic or hydropneumatic method. The hydraulic method involves using available system pressure and flowing water strategically through each system component in the same direction water would flow during a fire and is effective on obstructions comprised of loose material. The hydropneumatic method utilizes a special piece of equipment that takes compressed air and about 30 gallons of water and blows it from the end of a branch line back through the system piping and out an opening at the base of the riser. This method is necessary for compact obstructions that normal system pressure will not move.
In summary, within the scope of NFPA 25, 2002 Edition, Chapter 13, you are mandated to determine whether or not you have a problem with internal obstructions and/or MIC by completing an internal piping examination and obstruction investigation; if findings are inconclusive and no obstructions are found, then no further action is required. If you have obstructions that could plug sprinkler heads, you are mandated by NFPA 25 to correct the problem by having qualified personnel perform a thorough flushing procedure.
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