ISI is the Initial Spread Index; which factor does it most closely relate to?

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Prepare for the Edmonton Fire Rescue Services 159 Exam. Use flashcards and multiple choice questions, with hints and explanations. Ace your exam!

Multiple Choice

ISI is the Initial Spread Index; which factor does it most closely relate to?

Explanation:
Initial Spread Index measures how fast a small fire would spread in its early stages. It is driven mainly by how quickly flames can preheat and ignite fuels ahead of them, which is most directly affected by wind and slope. Strong winds push heat and flames toward unburned fuel and increase oxygen supply, while an uphill slope causes heat to rise and preheat fuels upslope, both speeding up initial spread. Fuel moisture, humidity, and ambient temperature influence fire behavior, but ISI specifically reflects the impact of wind and slope on the early rate of spread, not moisture-related effects or temperature alone. That’s why the best choice is wind and slope.

Initial Spread Index measures how fast a small fire would spread in its early stages. It is driven mainly by how quickly flames can preheat and ignite fuels ahead of them, which is most directly affected by wind and slope. Strong winds push heat and flames toward unburned fuel and increase oxygen supply, while an uphill slope causes heat to rise and preheat fuels upslope, both speeding up initial spread.

Fuel moisture, humidity, and ambient temperature influence fire behavior, but ISI specifically reflects the impact of wind and slope on the early rate of spread, not moisture-related effects or temperature alone. That’s why the best choice is wind and slope.

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