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Eliminating Sprinkler Ice Plugs in Cold Storage Applications

sprinkler ice plug

Sprinkler ice plug in pipe outside freezer

Ice plugs are a major problem in dry pipe fire sprinkler systems, particularly in cold storage applications. Ice restricts the flow of water, plugs piping and can prevent the sprinkler system from properly discharging water in the event of a fire. NFPA 25, The Standard for Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, requires freezers to be inspected annually for ice plugs, while some end users perform this inspection at more frequent intervals if they have previously experienced a problem.

When moist air from an air compressor is piped directly into the sprinkler riser within the heated area of the dry pipe valve, the water will condense and freeze as it enters the refrigerated space. The frozen condensate will eventually build up and plug the sprinkler supply main. To reduce moisture in the air supply, NFPA 13 recommends the air supply to be taken directly from the freezer space to obtain air that is relatively free of moisture. Sometimes the air is further dried with a desiccant or refrigerated air dryer before it is reintroduced into the freezer space.

Using Nitrogen to Eliminate a Sprinkler Ice Plug

A nitrogen generator provides several advantages over traditional air compressor/dryer configurations:

  • Nitrogen is an extremely dry gas that prevents moisture from entering the system and forming ice plugs
  • Nitrogen eliminates oxygen corrosion that occurs in supply mains outside of the cold storage area
  • sprinkler ice plug

    System supplied by nitrogen generator with no ice plugs

  • Nitrogen generators require much less maintenance than typical air dryers
  • Nitrogen generators can supply a significant volume of supervisory gas to multiple dry pipe sprinkler systems, minimizing the equipment needed at large facilities

Case Study: Nitrogen Generator vs Dry Air Pac in Cold Storage Facility

  • Total equipment and installation cost was equivalent between one nitrogen generator and two dry air pacs
  • Original installation of dry air pacs in four (4) riser rooms
  • Two (2) dry air pacs had reach the end of their life cylce and required replacement
  • In May 2016 one nitrogen generator replaced two dry air pacs
  • An internal investigation performed six (6) months later revealed the following:
    • Ice plugs found in dry pipe systems supplied by existing dry air pacs
    • No ice plugs found in systems supplied with the ECS nitrogen generator