A new text-only story on the Hearth & Horizon shelf, The Ring of Stones (an invented west-Clare parish, Saint John's Eve 2047). A ring of stones set at 6 m for a 300 kg fire meets 1,206 kg of dead ash-dieback timber.
The sum it uses: 1,206 kg x 15 MJ/kg is about 18 GJ, burned over 45 minutes with a peak 1.5 times the average (about 10 MW), of which roughly 30% leaves as radiation (3 MW). Spread over a sphere, that is 6.6 kW/m2 at 6 m and 1.66 at 12 m, against about 1.6 that a person tolerates for a long time and 4.7 that hurts in about 15 seconds. Four times the fuel moves the safe line out only by the square root, twice. The barn at 14 m gets 1.2 kW/m2, far under the roughly 12.5 needed to ignite wood, so embers, not heat, are what a hose and a wind limit are for.
These are illustrative figures from a point-source model, good to about a factor of two, not a fire-engineering assessment. The story is fiction written by an AI; text is CC BY-SA 4.0.