Hide a fire by burning dry seasoned wood in a small hot fire that gives little smoke, by sinking the flame below ground in a Dakota fire hole, and by cooking at midday when a thin smoke column blends into the haze. These methods hide flame and smoke but do nothing about carbon monoxide, so they belong outdoors only, and no flammable tarp or cloth may hang over the flame.
Part of Camouflage and Concealment
Fire and smoke management is the set of practices that reduce how far a cooking or heating fire can be seen, by controlling the light, the smoke and the timing.
A Fire Shows Itself Three Ways: Flame, Smoke And Smell
The parent article gives the visibility of a campfire at night as 5 to 10 km. By day the signal is the smoke column; at all hours it is the smell. A concealed fire has to be handled on all three. The methods below mainly reduce flame and smoke; smell is covered in Cooking Scent Control.
The parent article’s methods are:
- Dakota fire hole — two holes dug and joined by an underground tunnel. The fire burns in one hole; the other is an air intake. The fire burns below ground level, which sharply reduces the visible light, and it draws air through the tunnel so the smoke does not billow upward.
- Dry, seasoned wood only — dry wood makes little smoke; green, damp and treated wood make dense visible columns.
- Cooking at midday — a thin column at midday blends into haze and sun glare, where the same smoke at dawn or dusk stands out against a clear sky.
- Dispersing smoke — the parent article suggests a tarp or woven screen 2 m above the fire opening. See the warning below before doing this.
What You Need
- A digging tool and soil firm enough to hold a tunnel (not loose sand, not peat or root mat)
- Dry, seasoned hardwood in thin pieces, split small
- Water and a shovel to put the fire out completely
- Open air, outdoors, with no shelter around the holes
Method: Dig, Burn Small, Put It Out
Step 1: Choose the ground. Dry, firm soil, away from roots, peat, thick leaf litter and tree stumps. Fire can creep along roots and through peat and duff underground and re-emerge hours later and metres away. If the ground is not mineral soil, do not dig a fire hole here.
Step 2: Dig the holes and the tunnel. Dig a hole for the fire and a second for air, joined by a tunnel at the bottom. Keep both holes small, since a large hole means a large fire. The tunnel must be firm enough not to collapse onto the fire.
Step 3: Feed it thin dry wood. A small hot fire fed with finger-thick sticks makes far less smoke than a smouldering large one. A rocket-stove style burn chamber does the same job with less fuel; see Rocket Stove and Rocket Stove Design.
Step 4: Watch the smoke from the outside. Have someone stand where an observer would. The goal is that a thin or nearly invisible haze rises and disperses within a few metres. A solid column means wet wood or too much fuel.
Step 5: Put it out before you leave and before you sleep. Drown it, stir the ashes, drown it again and feel for heat with the back of your hand. Fill the holes and restore the sod; a scorched hole is a visible sign of a past fire.
Worked Example: How Far Away Can The Flame Be Seen Directly?
Take a fire pit 30 cm wide and 40 cm deep, with the flame at the bottom, and an observer whose eyes are 1.6 m above the ground. These dimensions are chosen for the example and are not a recommendation. The observer sees the flame directly only if the line from the eye over the near rim of the pit reaches the bottom of the hole within the hole’s width.
- The line drops 1.6 m for every x metres of horizontal distance from the near rim, so its slope is 1.6 ÷ x.
- It reaches the depth of 0.40 m after a horizontal run of 0.40 ÷ (1.6 ÷ x) = 0.25 × x metres past the rim.
- That run must be no more than the pit width of 0.30 m, so 0.25 × x ≤ 0.30, which gives x ≤ 1.2 m.
So the flame at the bottom of the pit can be seen directly only from within about 1.2 m of the rim, and from anywhere farther away it is hidden by the rim. A deeper or narrower pit shortens that distance further. What the pit does not hide is the glow thrown on overhead branches, leaves and smoke, and that can be seen from a long way off. The corpus gives no figure for how far that glow carries, so test it: have a helper walk out at night and note where the glow disappears.
Common Mistakes
- Treating the underground fire as invisible. It hides flame from low angles, not warmth, smell or the glow on overhead branches.
- Choosing damp ground. Wet wood makes the smoke you were trying to avoid.
- Leaving it burning in the hole overnight. A hidden fire in a hole can ignite roots and burn for days.
- Cooking at dawn or dusk by habit. The same smoke shows more against a clear sky.
Safety
Carbon monoxide, collapse, ground fire and a tarp over the flame
Never use a fire hole, an underground fire or any fire inside a shelter, tent, cellar or covered pit; carbon monoxide is colourless and odourless and kills in sleep, as Carbon Monoxide Risks explains. A tunnel or hole can collapse onto the fire or onto the person tending it. A fire in roots, peat or deep leaf litter can smoulder underground unnoticed and re-emerge. The parent article suggests stretching a tarp or woven screen 2 m above the fire opening; I have not verified that height and a plastic or cloth tarp that close to a fire can melt or burn, so use no tarp. If you want to break up smoke, use the foliage of living trees well above the fire, or cook less and use the haybox of Retained Heat Cooking, which needs only a short boil. Keep every fire clear of dry camouflage and put it out completely.
What’s Next
- Learn next: Artificial Light Control — the light sources inside the house
- Combine with: Signal Fires and Beacons — the opposite problem: a fire that is meant to be seen