Fire Proof Building

The past few summers I’ve been caught somewhat off guard by how vulnerable I feel when dry winds are blowing and smoke fills the sky. I remember very clearly being on the roof, with a mask on, cleaning out gutters and small piles of leaves. As an industrial hygienist, I know harm of dust and smoke from wildfires, but when the time came to protect my home I felt overwhelmed and unprepared. I remember looking around our valley and seeing tightly packed homes in the foreground with golden brown, grassy hills in the background. Trying to clean ash off my solar panels I caught myself thinking, “I wish I could enjoy a fire proof building.”

Can a Building be Fire Proof?

The short answer is no. At some point a fire is hot enough to melt steel and destroy concrete, and even before concrete is destroyed all contents within a building would be destroyed. So technically I suppose you cannot have a “fire proof” building. When a hundred structures are burning within feet of each other and the wind is howling in your direction, the only way to survive is to evacuate because the fire is too intense for any typically constructed building. However, experts now use the term “fire hardened,” and everyone agrees that you can significantly reduce the risk of catastrophic fire by following some simple recommendations. Just as I can look at a building and point out weak spots in moisture management and things that are likely to cause long term water damage or mold growth, a fire expert can similarly evaluate a building for fire risk. This obviously piqued my interest and now I’m happy to share these concepts with you.

Disclaimer: You cannot have a fire proof building. These concepts are borrowed from other sources and in no way should substitute for having a professional assessment, and engaging licensed design and construction professionals to harden your building. Finally, just reading this won’t do anything to reduce your risk. Get out there and make some improvements.

How Do Fires Start and Spread?

In order to understand the why of fire hardening, one must first understand how fires start and spread. Remember the fire pyramid?

Fires need fuel, oxygen and heat. (period)  If you eliminate any of these variables – you will extinguish a fire. Thinking preemptively, if you reduce any of these variables in a given area you reduce the risk of fire occurring.

Examples include:

• Fuel – Gases (e.g., propane, oxygen, etc.), liquids (e.g., gasoline, alcohol, etc.) and solids (e.g., leaves, trees, fences, decks, wooden siding, etc.) provide fuel for fires. Eliminating or protecting these fuels from fire is the most obvious means of fire hardening.
• Oxygen – Many fire suppression systems, such as fire extinguishers or helicopters dropping flame retardant foams, operate by removing oxygen from an active fire. Shoveling dirt over a camp fire is an example of suffocating a fire.
• Heat – Combustion requires an initial heat source. Ignition may start from a chemical reaction, lightning, electrical sparks, cigarette butts or a random ember flying from an unprotected chimney. Cooling materials will slow a fire, and if you remove enough heat fast enough, it will extinguish a fire.

Recent catastrophic fires in California have occurred in a perfect storm. Trees (fuel) have grown too close to power lines and eventually a spark (heat) starts a fire. Dry winds blow the fire across crispy fields and through forests full of dense undergrowth and standing dead trees. Intense fires create their own weather patterns with massive uplifts of wind which lift and carry embers far ahead of the actual blaze. Those embers ignite smaller fires ahead of the main fire, and by the time the main fire meets the smaller fire it’s a raging storm of heat and destruction. In some instances embers from wildfires have started fires up to a mile away from the big fire. Once in an urban setting fires jump rapidly from building to building, and embers fly into buildings and land in cluttered gutters and on dry wooden decks. The hot, dry wind distributes embers but also increases temperatures and desiccates materials so when ignition occurs it’s instant and the fire spreads very quickly.

Any building in the midst of a fire storm is unlikely to survive, but there are many things we can do to reduce the risk of fire in the more common “small fire” incidents to which we are accustomed. In every major fire the initial ignition source starts small. Taking these steps not only fire hardens your building, but takes steps toward reducing risk for your entire community.

Practical Fire Hardening Tips:

Creating Defensible Space

• Zone 1
  • Eliminate all combustible materials in Zone 1 (within 30 feet of the home) such as fire-prone vegetation, firewood stacks, combustible patio furniture, umbrellas, and dimensional lumber decking. Desirable substitutions include irrigated grass, rock gardens, stone patios, metal patio furniture, and noncombustible decking.
  • Before fire season begins, remove combustible litter on roofs and gutters and trim tree branches that overhang the roof and chimney.
• Zone 2
  • Ensure that Zone 2 includes only individual and well spaced clumps of trees and shrubs and/or a few islands of vegetation surrounded by areas with noncombustible materials.
  • Use hardscape features such as driveways and paved or gravel walkways or patios to create firebreaks throughout the yard.
  • Plant fire resistant, low volume vegetation that retains moisture well and needs minimum maintenance such as pruning and removing dead and dying branches.
  • Separate auxiliary structures such as a detached garage, pump house, pergola, and utility shed from the home by at least 50 feet. Increase the distance if the structure is used for the storage of combustible materials.
  • Comply with recommended construction practices related to fire resistance for auxiliary structures.
  • Ensure that patio furniture is either made of noncombustible material such as metal or is at least 30 feet away from the building. Store patio furniture in a location that is protected from ignition by a wildfire.
  • Place woodpiles at least 30 feet from the building and store the wood in a vegetation free zone such as a graveled area.
  • Store fuel tanks away from a structure at the minimum distance that is required by code or greater and place underground or on a noncombustible pad.
• Zone 3
  • Reduce fuels that are farther than 100 feet from the building by thinning and pruning vegetation horizontally and vertically as discussed above. Thinning and pruning in Zone 3 can be more limited than in Zone 2. The goals in Zone 3 are to improve the health of the wild lands and help slow an approaching wildfire. Zone 3 is also an aesthetic transition between the more heavily modified Zone 2 and the unmodified surroundings.