- The fire will continue to grow after the activation of a sprinkler in a dry pipe system. As the water travels the pipes in the sprinkler system the fire size grows. Therefore the designer should make the dry pipe system as small as possible.
- Sprinklers can only be installed in the upright position unless specifically listed dry pipe sprinklers are utilized or horizontal sidewall sprinklers installed so that water is not trapped.
- A dry pipe system is not intended to limit accidental damage from broken or open sprinklers.
- Sprinkler systems that are dry can not be gridded.
- The location of the dry pipe riser shall be heated to a minimum of 40 degrees F.
- Piping is pitched back to the riser so that water is not trapped.
Since the fire continues to grow while the water is traveling through the pipes, NFPA 13 requires that the design area of dry pipe sprinkler systems to be increased. This 30 percent increase is required by section 18.104.22.168.5 of NFPA 13. This added percentage is to provide additional water flow since it is likely that the fire will be larger, compared to a wet pipe sprinkler system installation.
If we compare two various systems installed in an attic area of a building. The changes in the system are either wet or dry pipe based on the lowest temperature in the space. If the attic space is maintained at 40 degrees F or higher, a wet pipe sprinkler system can be utilized. The design area may be based on a calculated density of 0.10 gallons per minute (gpm) per square foot over a design area of 1,500 square feet. If the area was not maintained at 40 degrees F, then a dry pipe sprinkler system would need to be installed. The density of 0.10 gpm per square foot remains the same, but a 30 percent increase on the design area would be utilized and a required area of 1,950 square feet would be required.
Proper installation of a dry pipe sprinkler system is critical. Improper system installation can lead to freeze ups or inadequate water delivery. The designer and inspector must work together to ensure a proper system which meets the code and the needs of the owner. As a responding fire fighter you should understand that each system initially operates differently and what the alarms associated with each system are. Next time you respond on a fire alarm at one of those big box warehouses, take a look at the systems and see if you can tell the difference between wet and dry pipe systems.
MICHAEL O'BRIAN, a Firehouse.com Contributing Editor, is a fire marshal for the Brighton Area Fire Authority in Michigan. He is the president of Code Savvy Consultants and is the creator of the dynamic webpage www.inspector911.com that is designed to assist all types of inspectors by providing resources, information, checklists and up to date news. To read Michael's complete biography and view his archived articles, click here. You can reach Michael by e mail at firstname.lastname@example.org..