Peeking Into The Pipe
Distinguishing between an ‘obstruction inspection’ and an ‘obstruction investigation’
NFPA Journal, September/October 2010
Internal piping inspection is an issue that received considerable attention during the development of the 2011 edition of NFPA 25, Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. Much of the attention focused on making a distinction between an "obstruction inspection" and an "obstruction investigation." In the 2008 edition of the standard, the inspection appears almost to be a subset of the investigation. In fact, the obstruction inspection is simply one of 15 different triggers for the more elaborate obstruction investigation.
The concept of the obstruction investigation of water-based fire protection system piping has been around not only since the first edition of NFPA 25 in 1992, but since 1980 in its predecessor document, NFPA 13A, Recommended Practice for the Care and Maintenance of Sprinkler Systems. That edition called for flow tests through carefully selected representative systems or lines to indicate general conditions throughout the premises. In selecting specific systems or lines for investigation, it was recommended that consideration be given to lines found obstructed during a fire or maintenance work, systems adjacent to recent repairs, or lines that simply involved long horizontal runs of feed and cross mains. Obstructions were most likely to be found in the most remote branch lines at the end of the longest cross main, particularly if the branch lines were located at a lower elevation such as under a deck or platform.
Today, the conditions that would trigger an obstruction investigation includes debris from the inspector’s test connection, evidence of pinhole leaks, or a 50 percent increase in the water delivery time for a dry-pipe system. An investigation may require that the system be flushed to remove the obstructions.
The concept of the obstruction inspection began with the 2002 edition of NFPA 25. Obstructions can enter the piping, such as through the use of fire department connections, or they can grow within the piping in the form of tubercles or corrosion. An obstruction inspection is a random internal inspection of the sprinkler system piping to check for any type of obstructions, including stones or welding coupons, that could block sprinklers. Indications of obstructions would warrant a more complete obstruction investigation, and, if slime or tubercles are discovered, the standard requires testing for microbiologically influenced corrosion. The inspection can take place when the system is shut down for another reason, such as a modification. In fact, NFPA 25 requires all systems to be shut down for maintenance at least once every five years for an internal inspection of check valves.
Evidence suggests that sprinkler systems need an occasional look inside. The German VdS insurance organization examined nearly 8,000 older sprinkler systems from 1998 to 2008. They found that, after 25 years of service, 3.5 percent of wet-pipe systems and 22.9 percent of dry-pipe systems contained heavy corrosion damage or considerable amounts of sediment, while another 31.3 percent of wet systems and 44.6 percent of dry systems showed corrosion and sediment in a threshold range.
While a random internal piping inspection is obviously not enough to ensure that all parts of the system are in proper working order, it does provide a relatively quick and simple check of the internal condition of the system piping. And that simple check can help ensure proper system performance in the event of a fire.
Russ Fleming, P.E., is the executive vice-president of the National Fire Sprinkler Assocaition and a member of the NFPA Technical Correlating Committee on Automatic Sprinklers.