One of the largest reasons the fire spread and started was because of the dry, arid, weather. For the past couple of months, Chicago was having dry weather. This affected Chicago majorly once the fire started. Once a small flame broke loose, it spread quickly because of the flammable materials surrounding the flames, such as dry wood, straw, coal, etc. Mrs. O'Leary seemed to have 2 tons of coal and 2 tons of hay in her barn, which impacted the fire very much.

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