What is the “chimney effect” and why do wildland firefighters fear it?
When serious accidents in vegetation fires are discussed, one question keeps coming up among wildland firefighters: What is the “chimney effect” and why do wildland firefighters fear it? This phenomenon, closely linked to topography, can turn an apparently controlled situation into a deadly trap.
What is the chimney effect in wildland fires?
The chimney effect occurs when fire spreads through gullies, canyons or ravines shaped like a funnel, where hot air rises with great force. The terrain channels the wind and hot gases upwards, accelerating combustion and narrowing the available space. The result is a sudden increase in fire intensity and temperature, right in the area where personnel may be located.
Why the chimney effect worries wildland firefighters
Wildland firefighters fear the chimney effect because it reduces their reaction margin to a minimum. In a deep ravine, the fire can “run up” over the crew at great speed, engulfing vehicles and people before they are able to evacuate. The combination of steep slope, accumulated fuel load and channelled wind means that any positioning error comes at a very high cost.
Warning signs and rapid decision-making
Identifying a possible chimney effect requires reading the topography before entering and throughout the entire operation. Narrow ravines, facing slopes and drainages that form a tube are high-risk areas. If the fire is at the bottom and the wind is blowing upslope, extreme caution is needed. Sudden changes in smoke direction, increased fire noise or embers rising forcefully are all signs to withdraw immediately to safety zones.
Self-protection and lessons learned in ravines
The best defence against the chimney effect is to avoid becoming trapped inside the topographic “tube”. Working from ridgelines, always securing escape routes and maintaining constant monitoring of the fire’s evolution are basic principles. In addition, vehicle self-protection systems and collective shelters can offer a last chance of survival if everything else fails. Every incident in ravines leaves lessons that must be integrated into training and into the safety culture of wildland firefighters so that the same critical situations are not repeated.