By Tim McNicholas

CHICAGO (CBS) — The Great Chicago Fire was a heartbreaking tragedy with an invaluable learning experience.

The catastrophe sparked a new approach to construction, city planning and fire prevention.

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Morning Insider Tim McNicholas shows us how those changes shaped the city we still know today.

“We had to completely rebuild an entire city,” said Chicago Fire Department District Chief Wally Schroeder. “If you look around the city you don’t see too many high rise buildings made out of wood. There’s a prime example.”

The legend of Mrs. O’Leary’s cow starting the fire by kicking over a lantern has long been disputed. However, something near near the O’Leary home started a fire that spread to a third of the city at the time. The fire killed more than 300 people and left 100,000 homeless.

One reason the fire spread so far and fast? Chicago was full of wooden buildings in close proximity to each other.

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“When we started re-establishing Chicago as a great city, we then started using concrete, brick, mortar,” said Schroeder.

In fact, laws were passed requiring those fire-resistant materials, and the tragedy put fire safety in the public spotlight. Potter Palmer even branded his rebuilt Palmer House hotel as the “only fire-proof house in the United States.”

Firefighters eventually started using the fire’s anniversary to promote public safety. In 1920, President Woodrow Wilson officially declared the first week in October National Fire Prevention Week.

The location of the O’Leary barn is where the city’s fire academy now stands. Schroeder says the department itself grew rapidly after the fire.

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“It’s always a reminder, of a great tragedy that occurred and how we can always do better.”

Tim McNicholas