A signal fire is safe and readable only if the ignition source, the stack of fuel and the ground around it are all prepared in advance: a stack on bare cleared ground, lit with a carried flame from the upwind side, with water or sand at hand and a watcher who stays until it is out. Fire carries the farthest of the visual signals but it also marks the signaller’s position to everyone in sight, so a fire alarm must be rare, pre-agreed and unmistakable from an ordinary cooking fire.
Part of Signal Systems and Communication
Fire signals use flame by night and a smoke column by day to send one or two agreed messages over distances that sound cannot cover.
The Fire Is The Hazard Before It Is The Signal
A signal that sets light to its own perimeter has failed. That is why the Early Warning Systems article allows a flare only as a hand-fired signal and never rigged to a tripwire, and the same test applies to every fire signal. The parent article describes pre-built fire stacks covered by a waterproof sheet, to be lit within 60 seconds; that is an untested claim, and nothing in the parent says where the stack stands or what it can ignite. Signal Fires and Beacons covers the siting and chain logic; this article covers the three things to settle for each fire.
- Ignition source. A carried flame (a torch, a lamp or a brand from a banked fire) lights the stack from the upwind side. A spark kit or match works but is slower with damp kindling; the 60 seconds must be timed on a rehearsal, not assumed.
- Fuel it spreads to. The stack, and anything within sparking distance: dry grass, a thatched roof, a hedge, leaf litter. The stack stands on bare earth or rock with a cleared ring around it that is wider than the height the flames will reach.
- Where sparks land. Embers travel downwind. If grass, a roof or a haystack is downwind within reach, the stack is in the wrong place.
Designing The Message
A single fire is ambiguous, as the parent article says, because it could be a campfire. Make the meaning depend on position and pattern, not on the presence of a fire.
- Place. Alarm fires burn only at the prepared signal site. A fire anywhere else has no meaning to the code.
- Pattern. Two fires side by side, or one fire and a second lit a fixed time later, are harder to imitate than a lone flame. The parent article’s three fires in a triangle as a distress signal is a wilderness-survival convention that neighbours may not know; if you use it, write it into the code table.
- Repetition. The parent’s “a fire lit and extinguished repeatedly” does not work with a built stack: you cannot put out a large fire in seconds. Use a count of fires, or two stacks lit in sequence.
Because any person can light a fire, a fire alone proves nothing about who lit it. See Authentication and Security.
Smoke By Day
Damp green leaves, grass or green boughs piled on a hot fire give a thick pale column. Resinous conifer wood tends to burn with darker smoke (recalled). The column must contrast with the background: pale against dark woods, dark against bright sky.
The parent article suggests black smoke from rubber, oil-soaked material or plastic. Do not use it. Burning rubber and plastics gives poisonous smoke that harms the person lighting it and anyone downwind, and the beacon article already limits fuel to wood. The parent also suggests pulsing the smoke by covering the fire with a wet blanket. Covering a hot fire releases a burst of steam and can burn the signaller; use two stacks or a count of fires to give a coded pattern instead.
Worked Example: How Far A Fire Can Be Seen
A stack on a 30 m hill, with the flame 2 m up, is at a flame height of 32 m above the plain. A ground watcher’s eyes are at 1.7 m.
- Fire’s horizon: 3.57 x √32 = 3.57 x 5.66 = 20.2 km.
- Watcher’s horizon: 3.57 x √1.7 = 4.65 km.
- Geometric ceiling: 20.2 + 4.65 = 24.9 km.
That is the Earth’s limit. A small fire is not that bright: Light Discipline puts a campfire at 5 to 10 km on a dark night, and the daytime smoke column depends on haze and wind. Use the ceiling for siting and the 5 to 10 km figure for planning, and test.
Diagnosing Failures
- Stack will not catch. Damp kindling or a leaking sheet. Store kindling in a lidded dry box and check after rain.
- Flame, but the next station does not react. The fire is hidden by a hill, a tree or a slight dip. Check the line by day, then at night.
- Smoke vanishes in wind. A strong wind tears the column; rely on a night flame or another method.
- A grass fire downwind. The cleared ring was too narrow. Re-clear and add water.
- Misread. The fire pattern collided with a burn the farmers started. Post the burn calendar.
Common Mistakes
- Lighting on a rumour. A false alarm costs trust at every station.
- Leaving the stack to burn out unwatched. Embers re-ignite after the flame dies.
- Burning rubber, tyres or plastic for colour. It is poison, not a signal.
- A stack beside a building or hay. Sparks reach it.
Safety
Signal fires start wildfires and give off poisonous smoke
Light only on bare ground with a cleared ring, never in a dry wind or a drought, and keep water, sand or a shovel at hand. Burn only wood and green vegetation. Stand upwind, keep clothing and hair clear of flame, and do not throw liquid fuel on a fire. A hand-fired flare may be used by a sentry who aims it deliberately; do not rig one to a tripwire. Stay until the fire is out and cold, and check the ground again later.
What’s Next
- Learn next: Lantern Signals — a much smaller light for night codes
- Combine with: Camouflage and Concealment — the other side of a signal that carries far