Sheltering in place is the last resort in a wildfire, for when leaving is cut off or too slow, and it works only in a building prepared beforehand: stone, earth or earthbag walls, a metal or earth roof, screened vents, non-combustible shutters, bare ground around it and water and tools inside. Nobody should plan to stay outside wetting the walls, because wetting a 260 m² building at even the ideal 0.29 L/min per m² needs about 75 L/min, so the preparation has to be done before the fire arrives.
Part of Fire Prevention in Settlements
Shelter-in-place preparation is the making ready of a fire-resistant building, with its supplies and a rehearsed procedure, so that people can wait inside it while a wildfire front passes.
A Refuge Is Chosen In Peacetime, Not In The Smoke
The fire guide says that sometimes evacuation during a wildfire is more dangerous than sheltering, and that a stone, earth or earthbag building with a metal or earth roof can survive a wildfire passing over it. Its steps are: close all windows and doors; wet the building exterior if water is available; block chimney openings to keep embers out; move combustibles from the exterior; fill sinks and containers with water; and gather everyone in the most fire-resistant building, the gathering hall or a stone structure. It says the fire front typically passes in 5-15 minutes and that survival depends on the building surviving that passage.
This corpus gives no test in which a building with people inside has been shown to survive a front, so treat the guide’s statement as a hope to design for and not a promise. Leaving early remains the plan (Wildfire Defense); sheltering is for when the trigger was missed or the route is cut.
Worked Example: Air, Heat And The Wet-Down For A Hall
Inputs: 150 people standing; a hall with a main floor of 100 m² and a ceiling 4 m high (assumed), so a volume of 400 m³; 150 ÷ 100 = 1.5 people per m², or 0.67 m² each, inside the hall guide’s standing allowance of 0.5-0.7 m² (Community Gathering Hall); resting oxygen use 0.25 L/min and carbon dioxide output 0.2 L/min per person, and heat output about 100 W per person (standard physiology figures, recalled and not read from this corpus); sealed, with no leakage.
- Oxygen in 15 minutes: 150 × 0.25 × 15 = 560 L = 0.56 m³, which is 0.14% of the 400 m³. Air holds 20.9% oxygen, so it falls to about 20.8%.
- Carbon dioxide in 15 minutes: 150 × 0.2 × 15 = 450 L = 0.45 m³, or 0.11% (about 1,100 ppm).
- In 2 hours, 8 times as much: oxygen down to about 19.8%, carbon dioxide about 0.9%.
- Heat of the occupants in 15 minutes: 150 × 100 W × 900 s = 13.5 MJ. The air mass is 400 × 1.2 = 480 kg; at 1.0 kJ per kg per K that is 480 kJ/K, so the air would warm by 13,500 ÷ 480 = 28 K if the walls took up none of it. They take up most, but a packed, closed hall can still become hot and stuffy.
- The exterior wet-down: walls of 2 × (10 + 10) × 3 = 120 m² and a roof of about 140 m² make 260 m². At the ideal 0.29 L/min per m² for a 12.5 kW/m² flux (Water Reserve Sizing), 260 × 0.29 = 75 L/min, over the whole 15 minutes, 1,100 L, and a bucket line delivers 50-80 L/min. So the guide’s wet-down cannot be done by hand for a building this size while the front passes, and no one can stand outside while it does.
Air is not the limit for a quarter of an hour. Heat, smoke and embers are.
What You Need
- A building of stone, earth or earthbag with a metal, tile or earth roof, and no thatch (Earthbag Building)
- Non-combustible shutters for every opening, fitting tightly, and curtains and bedding moved away from windows
- Screened vents and a closable chimney cap (Ember Protection)
- 10 m of bare ground or short grass around it, with no woodpiles (Defensible Space Zones)
- Water inside: barrels, sinks and buckets, and cloths for putting out spot fires
- Doors that open outward by pushing, with nothing to bar from inside
- A roster and a person for children, the sick and first aid
Method: Prepare And Run The Refuge
Step 1: Choose the building in advance by the list above, and mark it.
Step 2: Prepare it before the season: shutters fitted, vents screened, ground cleared, water barrels filled.
Step 3: On the trigger, if leaving is still possible, leave. Otherwise bring everyone in, close doors, shutters and the chimney cap, and count them.
Step 4: Assign a person to each opening inside, with a bucket and a damp cloth, to put out any ember that enters.
Step 5: Stay away from windows and doors while the front passes, keep low, and keep everyone calm.
Step 6: Do not go out until the front has passed and the heat has fallen. Then go out, put out spot fires on the roof and walls from the ground, and watch for hours, since embers keep igniting after the front.
Common Mistakes
- Choosing a thatched or shingle-roofed hall. It is the hazard, not the refuge.
- Counting on a wet-down. The arithmetic above shows it cannot be sustained from inside.
- Barring the door. A crowd needs to get out, and the outward-opening, pushing exit is the rule for any room holding more than a handful of people.
- Staying until it burns. If the building itself catches, the shelter has failed; know where the second exit leads before it comes to that.
Safety
Heat and smoke come through openings before the building fails
Radiant heat comes through open windows and gaps, and smoke and carbon monoxide through every leak. A building with an unshuttered window facing the fire or a vent that is not screened is not a refuge. Do not shelter in a vehicle, in a lightly built outbuilding, or in any room with a single exit and no ventilation. If the building catches fire, leave at once by the exit away from the fire, over bare ground, and do not wait to be sure.
What’s Next
- Learn next: Emergency Shelter Capability — supplies and capacity for a longer stay
- Combine with: Evacuation Routes & Assembly — the plan that comes first