(CNN) When a fire forced dozens of homeless people to leave their tents in Chicago's South Loop neighborhood, Jackie Rachev at the local Salvation Army was ready to welcome them.

Little did she know a Good Samaritan was paying to put them up in hotel rooms.

It's been brutally cold in Chicago, with temperatures of 20-25 below zero on Wednesday. The homeless encampment near the Dan Ryan Expressway was heated by 150 to 200 portable propane tanks -- many of them donated by generous citizens.

Shortly after noon, one of the tanks in the tent city exploded because it was too close to a space heater, CNN affiliate WLS reported . That left city officials with no option but to close the encampment and hurry to find shelter for the people living there.

"This is extremely unsafe," said Major David Byrd, the Illinois State Police Region commander. Thankfully, no one was injured in the explosion.

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