Monday, May 16, 2016

7 Sprinkler System Obstructions


"Plumbing" by Harsha K R

NFPA 25, Standard for Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems requires that an investigation of sprinkler piping be conducted to ensure that there are no obstructions.  This internal piping assessment is to be conducted, at a minimum, every 5 years.

What could cause fire sprinkler piping to become obstructed?  NFPA 25, Annex D lists and describes seven sources of sprinkler obstructions.

  1. Pipe scale - most commonly occurs in dry pipe systems that have previously had water through them then been allowed to dry; this can also result from condensation in dry pipe systems. Pipe scale are impurities in water that create a build-up in sprinkler pipes
  2. Careless installation or repair - this can result from parts, debris, or tools that are allowed to enter the system during installation and repair; these range from gloves, metal shavings, cutout discs/receipts, etc.
  3. Raw water sources - items and debris that is sucked into the system from the bottom of ponds, rivers, or reservoirs; this results when intake screens are not in place or properly installed
  4. Biological growth - primarily encountered in systems fed from a fresh water source (lake, pond, etc.);  the most common biological growth is the Asiatic clam.  The clam larvae enter and attach to the pipe, they feed on bacteria and algae that passes through
  5. Calcium carbonate deposits - this is an obstruction caused by "hard water" film
  6. Corrosion - "...deterioration of a material...resulting from a chemical or electrochemical reaction."  Common types of corrosion:
    • uniform corrosion
    • pitting
    • crevice corrosion
    • selective leaching
    • erosion corrosion
    • environmental cracking
    • intergranular corrosion
  7. Microbiologically influenced corrosion (MIC) - biological growth obstructions caused by microorganisms such as bacteria and fungi
For these seven reasons, ensure that an internal obstruction investigation is being conducted in conjunction with the fire protection systems 5-year NFPA 25 inspection.

Further reading: