BY ALBERT ROACH
Every year homes and businesses worldwide are lost due to wildfires. There is no doubt Firewise and FireSmart programs have improved fire safety. However, there are still many structures in the wildland urban interface with high potential for loss due to wildfire. Sprinklers set up to protect structures vulnerable to wildfire, have a proven success record. Wildland urban interface firefighters trained and equipped to use sprinklers will further reduce loss due to wildfire.
Sprinklers in Your Tool Kit
Sprinklers are a great tool to use in protection of structures from wildfire. Agricultural Sprinklers! The agricultural “impact” sprinkler that has been watering crops and golf courses for years is now an effective tool in the protection of structures from wildfire.
Structures protected by correctly positioned sprinklers, almost always survive wild fires. Unsuccessful outcomes, where sprinklers were correctly positioned, have been due to system failures such as pump break down or hose failure.
When fire approaches people try anything they think will save their home. They put lawn sprinklers on the roof, wet-down the house and yard before leaving yet often return to a total loss. What went wrong: “sprinkler position”! The water was not hitting the vulnerable places at the critical time.
Positioning sprinklers to keep fine fuels wet is the key to success. Sprinklers on top of roofs may give you a sense of security, but it is not enough as often the area next to the building stays dry due to leaves. By studying the reasons for structural loss in wild fires, and positioning sprinklers based on that information, you will have success.
To fully understand how a sprinkler can save structures from wildfire we must examine the fire behavior that leads to structure loss. Solid fuel must be heated to the point where there is enough fuel vapor coming out of the material to ignite (burning point). The faster fuel vapor can be produced in large enough quantity for burning to take place, the sooner you have self-sustained fire. Small combustible materials like grass or trigs (fine fuels) heat up quickly, they also dry out quickly compared to a log or 2×4 (heavy fuels).
The factors that govern the ignition of any material are: volatility, size, and flame (heat) to fuel proximity. Volatility refers to the speed a substance can change into a flammable vapor based on the material’s properties. That is: cedar, more volatile than ironwood, will ignite faster. The size of a solid will directly affect the amount and duration of the heat required to produce sufficient fuel vapor for ignition. That is: a spruce splinter will ignite faster than a spruce 2”X4”. Fuel proximity refers to the location of the fuel relative to an impinging flame or heat source. That is: heat is always greater above a flame than below it, so flame under a material will produce ignition faster than a flame above the same fuel.
The other factor related to structure ignition in wildfire is time. To sustain fire, ambient heat and flame impingement must last for a lengthy period of time for the large fuels to ignite and continue to burn. The time of extreme heating, depending on fuels and wind during the passing of a wildfire, is relatively short; generally, less than four minutes! Most large fuels do not reach burning point temperature in that short time period and are therefore easily protected with a small amount of water. Wildfires can turn into conflagrations in built-up areas, but the dynamics are different. In conflagrations, unlike wildfires, building to building ignition will take place without the presence of fine fuels due to the long-term high ambient temperatures. Therefore sprinkler placement requirements will be different.
In summary, when we build a camp fire we put twigs and other easy to light materials at the base and pile larger pieces of wood on top. The small material “fine fuel” lights quickly and builds sufficient heat to make the larger material burn. It is very difficult to make a camp fire burn without dry fine fuel. Wild fire moves quickly, the heat of a wild fire peaks and begins to drop at a speed that often is too fast to ignite large fuels. Fine fuels will ignite easily and just like kindling in a camp fire, can set larger fuels on fire. Sprinklers make the fine fuels wet and fire resistive. If the kindling won’t burn there will not be a camp fire. It is a very simple process: keep the fine fuels wet and the large fuel will not ignite!
Impact sprinklers deliver water in a circle. As the spray of water passes over fine fuels, the fuel becomes too wet to ignite. After the spray goes by, the fine fuel begins to dry, but before becoming hot enough to ignite the spray returns. In summary, heat must dry out fine fuel before it will burn and sprinklers keep fuel wet.
The location of fine fuels (kindling) is very important. If there is no fine fuel near any part of the structure and the exterior of the structure is fire resistive, the structure will most likely survive a wild fire without help.
In spite of the efforts of Firewise and Fire Smart programs, few are listening, even fewer are acting. The common thought, “it won’t happen to me”, is a significant opponent to the success of these fire prevention programs. In locations where home owners have taken the proper precautions and made their property wildfire smart, there are often neighbors who have not. The addition of sprinklers to a wild fire safety plan ensures better outcomes.
Impact agricultural sprinklers are ideal for structure protection and other wild land firefighting operations where sprinklers are needed for the following reasons:
· they are less susceptible to plugging from debris
· they have greater reach
· they are more durable
In order to use agricultural impact sprinklers for wild fire operations a mounting system providing for water delivery at ground level, in an elevated location and on a roof is necessary. Sprinklers come in ½”, ¾”, and 1” pipe thread, therefore, a waterway adapting them to garden hose fittings is ideal for fast and easy set up by homeowners, firefighters, and wildland firefighters. Sprinklers adapted this way are available from several different manufacturers.
Sprinklers Are Not Water Wasters
The objective is to make and keep the fine fuel wet while embers are falling and during the passing of the fire. Operating sprinklers for long periods before the fire’s arrival wastes water and provides little to no fire protection. Unnecessary property damage has occurred from excessive sprinkler operation. If a sprinkler has established a foot print before fire arrives and continues to maintain that foot print until the fire has passed, it has done its work.
A sprinkler will establish a footprint within a few minutes. Running sprinklers for longer time than is needed to establish a footprint has very little value as much of the water simply runs off or soaks into the ground. Small (3/4”) irrigation sprinklers equipped with a 3/16” nozzle can deliver the equivalent of .8 inches of rain per hour. Running sprinklers with that performance for several hours wastes water and can produce damage.
The amount of water required to protect a structure using sprinklers is far less than the water used by a structural fire fighter operating a single 1 ½” fog line. A sprinkler with a 3/16” nozzle will flow 8 gpm when operated at 65 psi. Depending on the size and configuration of a house it can be protected with as few as 2 sprinklers with 3/16” nozzles or 16 gpm. A 1 ½” fog nozzle can flow as much as 125 gpm. One minute of operation of a 1 ½” fog nozzle is equal to running the two sprinklers for over 7 minutes. It takes far less water to prevent ignition than it takes to achieve extinguishment.
Static water supplies are more desirable than hydrants as they will not reduce the water available to fire engines. When using hydrants it is important to establish how much stored water is available and if electricity is essential for hydrant pressure. Electricity often fails when electrical transmission lines are in wild fires. Not all fire water systems have a backup that will operate during power outages.
Sprinklers are often blamed for empty reservoirs after wild fire has destroyed several buildings. Sprinklers may have used a large amount of water, however, the major water loss was due to broken pipes at each of the burned down structures.
Fire fighter safety in wild fire is always a major concern. Every fire fighter that works ahead of a fire is taking a risk; the closer the fire, the higher the risk. Sprinklers do not require supervision they can be set up tested and turned on when all personnel leave the area. If sprinklers have been properly located, the system is protected, and the water supply lasts, structures will be standing after the fire. No one needs to be present during the most dangerous phase of the fire.
Guidelines for Sprinkler Set Up
· Where possible place the sprinkler high to simulate rain. Structures are designed to resist rain.
· All combustible material that is adjacent to the building or under decks must be wet.
· Easily ignited surface material on the building must be made wet.
· All parts of a wood roof surface must be wet.
· Avoid direct hitting of windows and doors or any other location that would allow water to enter the building.
· Test the set up to be sure all sprinklers are working correctly and that all targeted parts are getting wet before leaving the area.
· The sprinklers do not need to be operated for a long period before the fire arrives but they should be working all of the time that the fire is present.
· Protect the hose lines by burying them or keeping them under sprinkler protection.
· Pump sites should be sprinkler protected if they are on vegetation or any other fuel.
Sprinklers Work………It is hard to set wet things on fire!
ALBERT ROACH is president of A.S. Roach Fire Services Ltd., which provides structural and wildland fire protection consulting. He has served 47 years in the fire service and has held the titles of firefighter, engineer, instructor, chief, fire services advisor, wildland urban interface coordinator, safety codes officer, and fire protection consultant.