The Fire Blanket Solution for Fighting Wildfire

Overview

The fire blanket building protection system is similar to the mosquito net that relies on gravity rather than motor power as previously proposed. With this new system we can control the cost for protecting most buildings to be under $20,000.

Learning from mosquito nets

Unlike mosquito net with small holes, our fire fabrics are solid to prevent embers from entering. That said, I see at least two similarities between mosquito net and fire net. First of all, like the mosquito net, the fire net will rely on gravity to drop down from rooftop instead of relying on motor power to drag it up from the ground, which adds complexity and cost (we can retain it as an option for some households however). Secondly, we must secure the fire net in the ground, just like we secure mosquito net under our bed.

The common problem with these top covers: they are not big enough to cover the whole building and they add much cost to the fire net. In addition, several other issues must be solved.

How to make a big and wide fire net for the entire building?

Put differently, how to connect pieces of fire fabrics, which are typically one or two meters wide, together so that we can deploy the giant fire net instead of doing it in a piecemeal fashion. One way to do it is stitching. A faster way is to use multi-purpose reusable Velcro cable ties (or hook and loop tape or fastening straps) to quickly connect fabrics together.

An even cheaper option is to use fabric glues. We can easily find many permanent fabric glues in the market with very reasonable prices.

How to store fire fabrics on rooftop?

We will use round metal or better yet, PVC tubes /pipes with a small opening or slot to put the rolls of fire fabrics in. The tube structure should look like the picture below, except there should be two openings on the opposite sides of the pipe so fire fabrics can come out in different directions (see discussion later). All fire fabrics will be stored on rooftop, ready to be dropped down to the ground in the event of fire or fire alarm.

In order to make fire net to cover the entire building, from chimney to porch, we must build racks to hold the PVC pipes at the highest position on the rooftop. That way our structure can work with all types of roofs, flat or sloped, because the fire net does not need to be in touch with the building. We can truly make a “one-size-fit-all” structure.

The supporting rack will lift the fabric storage pipes to the highest position on the rooftop, allowing fabrics to roll down to the ground.

Rolling down and returning fire fabrics

We must find a way to easily pull fire net down in case of fire and then return it back to the storage pipes on the rooftop. A manual approach, not relying on electricity in case of power shutdown, is to borrow the mechanisms from Stanley Tape Measures, either the spring mechanism or more realistically the hand crank to roll down fire net from the rooftop and then return there.

This small tape measure uses spring mechanism to automatically role back after each use. For longer tape measures it always uses hand cranks similar to the one below.

Although neither spring nor hand crank requires electricity, manual movement of fire net is made easy by the fact that fire net is connected by fabric glues, and we can move a large piece of net down at a time, instead of piecemeal fashion because the fabrics are thin and light weighted.

For some households, we can add an automatic device that operates with electricity. The rolling down of fire net is achieved by guiding ropes or cables that are connected to the hooks on the end of fire net on the rooftop to pull it down.

When there is no fire, these ropes and cables are hiding along the roof, walls and lawn of the house. In the event of a fire alarm, they become visible and tightened by hand cranks (or electric motors, see before on installing and working with optional motors) to form straight lines from rooftop to ground ditches. When the fire is gone, we must crank reversely so these cables retreat to the slack and hiding position — by us as an extra service for the customers — while fire net return to the pipes on the roof.

Deploying fire net for sloped rooftops

This rooftop is the easier type, and we can make a long pipe to be connected in 90 degrees on each end by another tube. The long tube/pipe sits above the middle roof or the ridge, and then attach to the two tubes that sit on top of the other two sides of the building.

The entire structure looks like a capital letter “I” in horizontal position, or a dumbbell like shape. In case there are objects on the rooftop, such as antenna, we will raise the structure to be higher than those to ensure complete coverage of everything on the roof and also the entire building.

Deploy fire net for flat rooftops

We first build a tubular /pipe structure similar to the picture below to store fire fabrics to be deployed to the grounds in case of fires

This structure covers the four sides of the building, but we could have a round shape structure instead — if the building is largely round shaped. Either way, the structure should be located near the edges of rooftop, so they are ready to drop fire fabrics down to the grounds.

We also need to cover the roof itself. For that we can use structure similar to the patio umbrella (or several umbrella, depending on the size of the roofs and buildings), in the center of the roof and then attach one end of the fire fabrics to the umbrella, similar to this picture:

A simpler and cheaper solution is to have two slots on each tube or pipe, one toward the edge of the building and another toward the inner areas of the roof. Fire fabrics (or PVC sheet) will come out of the latter to cover the roof area, while getting out of the former to cover the sides, porch and backyard of the building.

Secure the fire fabrics in the ground

The fire net must be secured to the ground so that it would not be blown away — or even briefly lift up — by strong winds. Even a small opening gap is enough to let the fire embers in to ignite the whole building. We must design the fire net to prevent this from happening.

There are two keys to secure fire net. First, we can have holes at the near ground end of fire fabrics to allow hooks going through. The structure assembles shower curtain:

A simpler way is to use the fastening straps, or even better, magnetic bars for quick assembly:

The second key is to have ditch surrounding the building on the ground, and to secure fire fabrics in the ditch. The crucial detail is to let the fire fabrics go through the rod and wrap it so there is no gap left open.

Budgetary Considerations

The fire net covers the entire building so we must estimate the total surface area of a solid object — the building in order to get a rough idea the size of fire fabrics needed for a typical building. Below we will make several simplifying assumptions.

We know the average houses are 2,700 sq. Ft in the US (a real figure from online), which translates into 250 sq. meters. Assuming each square meter of fire fabrics cost $7, and further doubling the average building to be 500 sq. meters (5,382 sq. ft.) to allow coverage for backyard, lawn and porch, then each side is the square root of 500 = 22.36 meters or 241 ft. (assuming the house has a square base for simplicity).

Next, we must add in the height of building. Let us assume the roof is 1.5 meters or about 5 ft. high. For sloped roofs we have essentially two triangles plus two rectangular (see the pictures before on sloped roofs). The triangles are on the side of the roof, while the two rectangular are the sloped roofs. We already know that each side of the house is 22.36 meters or 241 ft., so the base of the roof has an area of 22.36 * 22.36 = 500 sq. meters or 5,382 sq. ft. Now to get the area of the sloped roofs (the rectangular) we multiply 22.36 (length of the roof, same as side of the house) by 1.5 (height of the roof) to have 33.54 sq. meters (361 sq. ft.) With two sloped roofs we have 33.54*2= 67.08 sq. meters or 722 sq. ft.

For the two triangular sides, the area is ½*base*height=0.5*22.36*1.5=16.77 sq. meters or 181 sq. ft. With two sides we have 16.77*2=33.54 sq. meters or 361 sq. ft. Adding up the four sides we have 33.54+67.08=100.02 sq. meters or 1,077 sq. ft.

Now let’s calculate the surface areas of the house below the roof. We already know that each of the four sides of the house is 22.36 meters or 241 ft., now we need to find out the average height of the house. That average height according to ARXIV.ORG (https://arxiv.org/pdf/1512.00946.pdf) is 6.3 meters or 76 ft. (based on 12 cities height data using LiDAR, or Light Detection and Ranging measures of roughly 4.8 million buildings in the sample).  Now, since we have assumed the roof height is 1.5 meters, the rest of the house must be 6.3 – 1.5 = 4.8 meters or 16 feet. The area of each of the four sides (i.e., four walls) of the house is 22.36*4.8=107.33 sq. meters or 1,155 sq. ft. With four sides (or four walls) the total area comes to 107.33*4=429.32 sq. meters or 4,621 sq. ft. Adding back the roof total area of 100.02 sq. meters we have 429.32+100.02=529.34 sq. meters or 5,698 sq. ft. This is the total area of the house that needs to be covered by fire net. Notice the areas of porch, lawn and backyard are already included in the total of 500 sq. meters.

For now let us assume the price per sq. meter of the fire fabrics is $10 (we can go lower or higher than that), then to cover the total of 529.34 sq. meters we need $5293.4, which is less than the price of two brand new refrigerators that I found in Home Depot (unit price is $2,799, the brand is Bosch, $2799*2=$5,598).

If the refrigerator price is not typical, we can have another more convincing reference. Let’s calculate the average cost of all kitchen appliances in 2019. According to the website https://www.improvenet.com/r/costs-and-prices/kitchen-appliance-cost-estimator, the minimum price for a side-by-side door refrigerator is $700 and highest $2,100, the average of the two is $1,450. For the gas range, the minimum is $350 but the maximum $2,000. The average is $1,175. A separate cooktop can be $300 for four burner type but $2,500 for induction cooking, the average is $1,400. A dishwasher is minimum $250, but max at $1,000. The average comes to $625. A blender costs minimum of $25 but max $200, the average is $112.5. A toaster over is minimum $40 and max $175, the average is $107.5. A microwave oven costs between $80 and $300, the average is $190.

Adding up, a modern kitchen with average appliances costs a total of 1450+1175+1400+625+112.5+107.5+190=$5,060. This is a good reference price for our price of $5,293.4 for fire fabrics.

There are other ways to save money. For example, www.tableclothfactory.com has a deal that for 2 Pack | 5FTx10FT Black Fire Retardant Polyester Curtain Panel Backdrops With Rod Pockets for $38, each pack of 5FT x 10FT =4.64 sq. meters is $19. Now dividing the total area of 529.34 sq. meters by the 4.64 to have 529.34/4.64= 114 units, which then times unit price of $19 to have 114*19=$2,168!

Now we can confidently control the entire fire net to $5,000 in total cost. Given the average house price in the USA is $279,500, the cost of fire net is less than 2% of house price: 5000/279509=0.0179 or 1.8%. Even if the total budget for fire net is $10,000, it is still way less than 5% of the house market value: 10000/279500=0.0358 or 3.58%.

An even more interesting comparison is private firefighters. According to NY Times https://www.nytimes.com/2019/10/26/style/private-firefighters-california.html, the wealthy in California are hiring private firefighters to protect their valuable homes for up to $3,000 per day. What these private agents do? They are not directly fighting the flames but rather “They focus on making homes more fireproof by installing sprinkler systems, fire breaks and fire-blocking gels.” Also, “The majority of private fire crews work for insurance companies like Chubb, USAA and Safeco, which often provide fire mitigation services to their policyholders in high-risk fire areas without extra charge.”