Oak Hill Area FSC | Considerations for Building Fire Bunkers
What are the reasons people consider building fire bunkers?
- Some people who build bunkers are worried that they won’t be able to get out if a wildfire strikes.
- Others are concerned about the awful possibility of being stuck on one of our dead-end roads in the middle of a fire.
If you are determined to add a fire shelter or bunker to your fire survival plan, we offer thoughts about preparing a well-designed fire bunker at your home well in advance of any need. Keep in mind that creating a fire bunker - a place to shelter in place as safely as possible - can be quite costly.
Sheltering in place in an emergency is covered in detail in the "Save Your Life" page. Be sure to take a look at that page.
Wildfire is ERRATIC, UNPREDICTABLE, and usually UNDERESTIMATED. Life safety is always the most important consideration! Homes and things can be replaced. Your life cannot.
Remember: Evacuating early is just about always the best option for saving your life.
A shelter could be your home, an outbuilding, or shop that has been well-hardened against ignition, and has an adequate defensible surrounding.
A bunker is a shelter that is partially or fully underground- this is generally best for heat protection.
To maximize the likelihood of survival in a firestorm you need to be inside the shelter until the flaming front passes. That can often be just 15-20 minutes, but sometimes a firefront can turn back and reburn an area all over again. Findings from Australia's Black Saturday fires indicate suffocation and heat were the primary reasons people perished when sheltering. Smoke inhalation can be another cause of death.
Even though evacuating early is recommendedm, some people really want to shelter in place - they want to stay and defend their homes against spot fires that can go on long after a main fire front has passed.
This is not something to decide lightly. Are you sure that’s worth risking your life for? And putting firefighters who might need to save you in danger also?
Sheltering in place was at one time promoted in Australia, where many people live quite remotely, but the deaths from people who stayed during their terrible “Black Saturday” event of 2009 made people even there rethink the strategy. 180 people lost their lives, including some who thought they were safe in prepared shelters.
It is critical that your space is air-tight, has enough oxygen for the occupants, and is very well-insulated. According to USFS National Technology and Development, wildland fires are typically 1,600 degrees Fahrenheit and sometimes reach 2,000 degrees or more. Humans can tolerate 300 degrees Fahrenheit for a brief time and 250 degrees Fahrenheit for an extended period. Underground bunkers offer the greatest protection from heat exposure of an intense fire.
Stair access that has a three-hour fire door or hatch and a smoke-proof and airtight seal, or two sets of fire doors for radiant heat protection.
A special roll cage that is designed to stop debris from blocking the exits
A fire bunker must be made out of appropriate materials. Some options:
- Concrete: Reinforced concrete set into the ground deep enough so as to not be compromised (explode) from intense fire
- Wood: Built underground similar to a basement. Very thick timbers that char rather than burn rapidly, buying you time while the fire front passes
- Prefabricated: Specialized concrete reinforced with steel. Often modular in design and sometimes available as kits. Completely buried or partially exposed.
(information borrowed from Australia)
- Between 30 and 130 feet from your main home, with an entry door facing the principal dwelling - consider age, disabilities and other physical limitations as you choose your site.
- At the end of a clearly marked, non-slip access path that is straight, level, and obstacle free
- 30 feet or more away from outbuildings, garages or carports
- 30 feet or more away from other fuel sources, such as firewood piles, farm equipment, etc.
- Where any nearby trees have been removed or at least trimmed of branches that could fall on bunker door
- Where other vegetation is kept at a minimum or completely clear around the bunker
- Where there are no other combustible or non-combustible objects that could fall onto a bunker door because of wildfire generated winds
QUIZ: Should I stay or go?
Even if you have a prepared shelter, wildfires can be noisy, dark, incredibly hot, and very scary. Wildfire fatalities most commonly occur when people leave their homes too late and are overtaken by fire. If you are thinking that sheltering in place might be for you, take the Quiz below to assess your preparedness. If you answer “No” to any of the questions, plan to evacuate early.
The quiz below was designed for Rancho Santa Fe fire safe communities, where the whole community was built with fire protection in mind. Homes have boxed in heavy timber or ignition resistant eaves with no vents, residential fire sprinklers, adequately wide 2-way roadways and driveways, good water supply and water flow, 100 ft defensible space throughout the whole community, dual paned windows throughout, with one of the panes being tempered glass, etc.
Questions to consider about whether to stay or go for Rancho Santa Fe residents, and for you if you have a truly effective shelter. (Questions are based on people sheltering during the fire front itself, and then staying in the aftermath to put out spot fires.)
- Are you physically fit to fight spot fires in and around your home for up to 10 hours or more?
- Are you and your family members mentally, physically, and emotionally able to cope with the intense smoke, heat, stress and noise of a wildfire while defending your home?
- Can you protect your home while also caring for members of your family, pets, etc.?
- Do you have the necessary resources, training, and properly maintained equipment to effectively fight a fire?
- Does your home have defensible space of at least 100 feet and is it cleared of flammable materials and vegetation?
- Is your home constructed of ignition-resistant materials?
If you answered “No” to any of these questions, then plan to evacuate early.