If your building or facility has an area that is subject to temperatures that can fall to below 40o F, chances are it is protected with a dry pipe sprinkler system. Dry pipe sprinklers systems are designed specifically for areas subject to freezing, where the use of traditional wet pipe fire sprinklers would result in burst pipes and damage to the areas they are intended to protect. This post will take a closer look at dry pipe fire sprinklers to help you become more familiar with these systems and how they work.
Dry pipe sprinkler systems are ideal for:
- Parking garages
- Unheated warehouses and loading docks
- Unheated attics
- Commercial freezers and refrigerated coolers
- Outside canopies attached to a heated building (e.g., retail garden centers)
How a Dry Pipe System Works
Contrary to what some might think, a dry pipe system does not use dry chemicals to suppress a fire. Like wet-pipe sprinkler systems, dry pipe systems use water to suppress fires. However, in contrast to a wet pipe sprinkler system in which the pipes are filled with water at all times, the unheated pipes in a dry pipe sprinkler system are instead filled with pressurized air and/or nitrogen. While the system is connected to a water source, the water is held back by a dry pipe valve, which remains closed until the system is activated.
Dry pipe sprinkler systems use closed-type sprinkler heads, which work in combination with the dry-pipe valve to activate the system when needed. The pressure holds the valve in the closed position. When heat activates one or more of the sprinkler heads, they open up, allowing the system's pressure to drop. When the pressure drops, the valve opens and releases the water into the system to flow through the activated sprinkler heads.
Advantages of a Dry Pipe Fire Sprinkler System
Wet pipe sprinkler systems are typically the go-to system for most businesses. They are reliable and straightforward and work instantly -- the water in a wet pipe sprinkler system doesn't have to travel far as it is available right at the sprinkler heads. However, when it comes to protecting areas subject to freezing temperatures, dry pipe systems become an obvious choice when considering the alternatives, especially if the area to be protected is very large. Using wet pipe systems in large areas exposed to cold temperatures can be very costly as they require a lot of insulation and heat tracing to keep them warm.
There are some older sprinkler systems out there that still use antifreeze solutions containing propylene glycol and/or glycerin. However, due to these compounds' combustibility, the National Fire Protection Association (NFPA) has required that all systems using traditional antifreeze solutions be replaced with alternative freeze protection methods by 2022. One alternative is to replace the traditional antifreeze solution they contain with one that has been tested and proven non-combustible when released from sprinkler heads. However, such solutions are just now coming to the market, making it unlikely that they will be widely available in time to meet the NFPA mandate.
The chief benefit of a dry pipe system is that its pipes are never in danger of freezing, which can release water into the area when it is not needed, potentially causing property damage and requiring costly cleanup.
Dry pipe sprinklers also offer "precision" fire suppression. In a dry pipe sprinkler system, each sprinkler head in the system operates independently, which means that sprinklers will only activate in the area in which fire suppression is needed.
Disadvantages of a Dry Pipe System are Relative to Your Needs
As with any system, there are advantages and disadvantages. And when it comes to sprinkler systems, the decision of which type of system to use will be largely determined on the context -- the specific conditions you are dealing with and how the area in question is used. If your situation requires a dry pipe system, any comparison to wet sprinkler systems becomes moot. Assuming the area you need to protect requires a dry pipe system, characteristics that could be considered disadvantages compared to a wet pipe system become factors you need to consider before investing. We offer a few of those factors here.
Installation and Maintenance Costs
In terms of costs, you can expect a new dry pipe sprinkler system to require a greater upfront investment than a wet pipe system because it is a more complex system both in terms of the equipment required and the labor needed for installation. Dry pipe systems require additional control equipment and an air compressor. With additional equipment come additional maintenance costs as well.
Dry pipe systems also come with more design restrictions, which means that installation will be more complex. For example, the strict requirement regarding the maximum permitted size of an individual dry pipe system (750 gallons) can make it difficult for an owner to make system additions later. This particular restriction makes it very important to consider both present and future needs when designing the initial system.
Dry pipes are also more susceptible to corrosion than the pipes used in wet pipe systems. While dry pipe systems are designed to keep water out of the system until activated, water can get into the pipes. This can occur when the air's humidity turns into condensation when the air in the pipes is pressurized. Residual water can also remain in the pipes after activation or testing. When combined with the pressurized oxygen in the system, this moisture can cause internal pipe corrosion, leading to pitting and small leaks in the pipes over time.
Corrosion in dry pipe systems can be mitigated with copper or stainless steel pipe, both of which are less susceptible to corrosion and/or with the use of dry nitrogen gas instead of air to pressurize the system. While these precautions can add to a higher initial investment, if your situation requires a dry pipe system, they can pay off in the long term.
It is essential to know that while a dry pipe system offers more precise protection than wet pipe systems, it can take up to 60 seconds from initial activation to when the water reaches the sprinklers. The main concern here is that this delay can lead to more damage before the fire is suppressed. However, when considered within the context of a wet vs. dry system, the risk of frozen pipes likely far outweighs the risk of a 60-second delay in fire suppression. Here again, if the area you need to protect requires a dry pipe system, this delay need not be a primary factor in your choice of the manufacturer because it is inherent in the system's design. All dry pipe systems will have this delay.
Maintenance is Key to Avoiding Premature Failure
Routine maintenance of dry pipe systems is critical to avoiding their failure and containing ongoing costs. If not properly maintained, these systems can freeze and flood the areas they are intended to protect. When this happens, you not only have a costly cleanup on your hands, but the system is rendered inoperable, which triggers the requirement for a fire watch until it is repaired.
The maintenance requirements for dry-pipe sprinkler systems can be found in the National Fire Protection Association (NFPA) 25 Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.
If your building or facility requires a dry pipe sprinkler system, Koorsen Fire and Security can answer any questions you might have and design a system that will meet your needs today and into the future. Our experts can also help you maximize the value of the system you have performing all the required inspections and testing to keep it in proper working order. Contact Koorsen today to schedule your next inspection.