Firenet to Contain Prescribed Burns and Protect Property

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Caitlin Cannon
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Firenet to Contain Prescribed Burns and Protect Property Design Team Oyedotun Ajewole, Alex Cooley Veena Kothapalli, Eng Ly Design Advisor Prof.

1 Firenet to Contain Prescribed Burns and Protect Property Design Team Oyedotun Ajewole, Alex Cooley Veena Kothapalli, Eng Ly Design Advisor Prof. Yiannis Levendis Abstract Traditional methods of combating forest fires include creating firebreaks and releasing water or chemical retardants. However, these methods do nothing to stop the fire from being spread by burning embers carried by the wind, which leads to fires jumping distances over a mile long. Often, wildfires start as prescribed burns, which are intentional, controlled fires but can get out of control if the fire jumps. A large, netlike, fire retaining structure has been designed that will give firefighters more time to combat the flames on the ground by reducing the spread of fire by airborne embers during prescribed burns that are threatening to grow out of control. The method of deploying such a net has also been taken into consideration as part of the overall design. For effective usage, the deployment method allows the net to be used quickly and with mobility. By folding or rolling the net in conjunction with scissor lifts, it can be easily transported and deployed by a small number of people, making it usable at the site of almost any prescribed burn. For more information, please contact yal@coe.neu.edu.

2 The Need for Project Fire personnel have no way to control air-spreading of embers during prescribed burns except to chase them and extinguish them manually. The Firenet will catch embers before they spread outside of the burn area. Currently, when a prescribed burn is performed, there are several methods used for ensuring the fire will not break out of the burn unit, the area designated for burning. However, these methods, which focus on clearing out ground fuel, do nothing to prevent fire spreading through the air by way of burning embers. When fire spots over firebreaks, the only control in place is to have fire personnel see, chase, and manually extinguish each ember and the fire it causes. The Firenet, placed in crucial areas around the perimeter of the burn unit, will catch these embers, eliminating the need for fire personnel to locate and chase each spotting ember. The embers, upon hitting the net, will extinguish when caught or will fall onto an area clear of ground fuel. The Design Project Objectives and Requirements The Firenet must be large enough to block off a targeted area from embers, but also light and mobile. The material of the net itself must be nonflammable, have low drag, and stand up well to use, while the deployment method must be strong enough to support the weight of the net and the force of wind. Design Objectives The Firenet must be large enough to catch embers coming from the tops of small trees, which are sometimes burned in prescribed fires. Research into prescribed burns has shown that the net should be at least 50 ft. high and in order to be useful should be at least as long. At the same time, it should be light and mobile enough to be transported to the site of a fire; it should not take more than 2-3 people to transport and set-up and must be able to be carried by small vehicle. Design Requirements The net must be as big as stated above and should be less than 200 pounds, the limit for ergonomically safe lifting by a 2-3 individuals. It should be able to withstand the heat of a burning ember, which can reach up to 550º C. The holes in the net should allow sufficient air to pass through in order to minimize drag force when wind hits it; a drag coefficient of less than.15 is desirable (Rep. 4.1).

Design Concepts Considered Thirteen materials were tested, of which 3 passed all tests. Four deployment methods were considered, of which two were feasible.

These were the only materials with physical properties that could withstand the heat but were not too expensive or too dense.

3 Design Concepts Considered Thirteen materials were tested, of which 3 passed all tests. Four deployment methods were considered, of which two were feasible. Net Material Thirteen materials were initially considered and tested for the net, including 304 stainless steel of various wire thicknesses and weave patterns, 316 stainless steel, and nickel. These were the only materials with physical properties that could withstand the heat but were not too expensive or too dense. These 13 materials were put through tests involving direct flame and burning debris, and each passed, sustaining only cosmetic damage, but no physical damage. Of these 13, 9 were then eliminated based on the lack of flexibility in the weave pattern and thickness. The remaining materials, two 304 SS, a 316 SS and nickel, were tested in a wind tunnel to determine their drag coefficients. With this test, the nickel was eliminated for having too high of a drag coefficient and the 304 SS with meshed weave pattern had the lowest and thus became preferable. These three remaining steels were put through a tensile test and the meshed material again was found to elongate the most before critically deforming (Rep. 4.2). Deployment Method Several possibilities were considered for deployment such a large net, including by air, land, and having stationary nets. Dropping the net by air was excluded early in the design process as this would be less effective, would require more resources, and would only be used in emergency situations. Placing nets in critical, stationary locations where they could be unrolled was also considered, but decided against, as this would require users to purchase too much material that might never be used. Finally, two mobile methods were considered. The first was an umbrella concept, whereby the net would unfold like an umbrella from the middle of the fire and surround it on all sides, even from above. The second was to have the net behave more like a wall between two supports rather than around the entire fire. Several of these could be used in conjunction with one another. Eventually, the latter concept was chosen because it would require less material and thus would be easier to set up and transport, and would cost less to the end user. Securing the area above the fire with the umbrella was not as important, and the umbrella would have to be directly in the fire.

Recommended Design Concept The recommended design utilizes two supporting scissor lifts on either side of the net. The net rolls down and folds to become mobile and is unfolded using the lifts.

4 Recommended Design Concept The recommended design utilizes two supporting scissor lifts on either side of the net. The net rolls down and folds to become mobile and is unfolded using the lifts. Design Description The final design incorporates the net and deployment system in tandem. The net size can be modified according the user needs, but for the purpose of experimentation the model correlates to a 50 x50 net. It is supported on either side by two industrial scissor lifts (dieselpowered) that are self-driven with 4-wheel drive and extend to the full 50 feet in height, but when are less than 8 high when compacted. The net will be attached using flexible but strong rubber connectors that are able to twist to allow for the rolling and unrolling of the net as the lift moves up and down. The net is flexible enough to roll in two directions, making it compact and transportable. The lifting mechanism will provide enough force to lift the net, which will weigh approximately 160 lbs. Experimental Investigation Flame Tests The flame test, mentioned above, proved that the material can withstand a sustained flame over 550ºC for several minutes, whether direct flame (Bunsen burner), or burning debris (wood, leaves, etc.) (Rep ) Analytical Investigation Wind Test & Tensile Test The wind test showed that the selected material has a drag coefficient of.11. Using this, the force on the net from 20, 40, and 60 mph winds was determined. This, together with the information from the tensile test, including Young s Modulus, enabled further calculations to determine the effect of such forces on the overall structure (Rep ). Analytical Investigation Structural Integrity It is crucial to understand how wind forces will affect the structural integrity of the overall system. The wind blowing on the net creates a tension in the net which translates to forces on the scissor lift itself in the form of bending stresses. ANSYS was used to model these forces and determined that the tension caused by drag force will not cause excessive bending in the lift supports (Rep 4.4). Key Advantages of Recommended Concept The wall-like net structure is easily the most mobile and easiest to set up of all the considered designs. It is strong enough to withstand outside forces but light and flexible enough to be quickly deployed.

5 Financial Issues The net itself is likely to be greater than $5,000 to manufacture. However, billions of dollars are spent annually in reparations when prescribed burns go awry. The net material itself, while relatively inexpensive at less than $4.00 per square foot, will become expensive simply because of the overall net size. When bulk ordering and manufacturing is considered, this price will likely become much less. Moreover, the net will be reusable if the fire does not grow completely out of control and engulf the entire apparatus. Industrial scissor lifts range from a few thousand dollars to over $20,000. It is unclear whether the market would be best-suited for retro-fitted nets for existing scissor lifts or if they should be sold together with available lifts. Although this overall cost may seem high, it is quickly offset by the billions of dollars spent each year in damages and payouts when prescribed burns grow out of control. Recommended Improvements The design could benefit from further investigation into connectors from the net to the supports. From a marketing point of view, much research needs to be done to determine how to best group the net and deployment device in sales. The design could benefit from more research into an optimal connector to join the net to the lift supports. The basic requirements are that the material is flexible or twistable, so that the net can roll and unroll, but a trade-off between strength and flexibility exists in this small component that has not been fully explored. From a sales and marketing perspective, it is crucial to understand whether customers would be interested primarily in purchasing the net by itself to attach to their own lifts, or whether they would be purchasing, or even renting, lifts for this specific purpose. In the latter case, a redesign of available lifts might be necessary to reduce costs, as all the features of industrial lifts might not be necessary.

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