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March 2005: Maintaining Dry-Pipe Sprinkler Systems

The owner of the large glass plant couldn't remember the last time he tested the building's dry-pipe sprinkler system. The facility had been sitting idle for at least a year, and he had three other busy locations to focus on.

Unfortunately, in the early morning hours, a fire started in the building's 200,000 ft. storage area that was filled with combustible storage. A corroded clapper in one of the dry-pipe valves failed to open, preventing water from reaching the sprinklers, and allowing the fire to engulf the entire storage area and the surrounding buildings. By the time the fire was extinguished several hours later, the loss was calculated in the range of $30 million.

It is an expensive lesson to learn and one that could have been avoided if the plant's operator had instituted a regular dry-pipe inspection, testing and maintenance program.

Understanding Dry-Pipe Systems

A wide range of industries relies on dry-pipe systems for their sprinkler protection. Most of these industries have operations in colder climates or the systems are installed in areas that are not practical to heat. These businesses may include paper mills, saw mills or other operations where handling the product involves moving from the outdoors to the indoors. Other industries, such as food processing and storage, require the buildings be kept at low temperatures to maintain the quality of the product.

Preaction type dry systems are often used in freezers, coolers, computer rooms and where detectors are used to actuate the pre-action valve. These installations are more complex and potentially less reliable.

For effective fire control, the building's automatic sprinklers must receive an unobstructed flow of water. The most common material used for sprinkler systems is uncoated ferrous metal (iron). When the pipe is exposed to water and air, its internal walls will oxidize. This corrosion leads to scaling which can obstruct the sprinkler head orifices. The result could be greater fire damage, an excessive number of sprinklers operating during a fire and even a threat to the structural integrity of the building.

Current standard recommend galvanized pipe for new dry system installations. But, there are still many older systems that use uncoated pipe in places where you can't prevent the corrosion from happening. All you can do is periodically remove the scale accumulation.

Recommended Testing Periods

The key to ensuring the best possible outcome of any emergency is a well designed and documented formal inspection, testing and maintenance program as indicated in NFPA 25, "Inspection, Testing and Maintenance of Water-Based Fire Protection Systems." Major items include:

• Dry pipe should be trip tested once per year. This will ensure the clapper is free to operate in an emergency.

• If the system is composed of black steel dry-pipe, it should be flushed when a system is 15 years old, 25 years old and every 5 years thereafter.

• An adequate source of air is needed to maintain proper air pressure for the system. This can be from a dedicated air compressor or a connection to a plant wide system.

• The dry pipe valve room or enclosure should be at least 10 degrees above freezing and provided with a reliable heat source.

When properly designed and maintained, a dry or preaction system should provide the same level of protection as a wet system.

Risk Logic can assist in helping you determine if your dry or preaction sprinkler system is in proper working order and up to current standards. We can also assist in designing a system for a new occupancy.