Temperatures at Chicago's O'Hare Airport were at -20 Wednesday morning.
And wind chills are making those dangerous numbers feel even lower: the -30s, -40s, and -50s.
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While the Arctic blast hits, rail crews worked to prevent and fix pull-aparts -- a rail defect where two rails separate at their connection.
According to Chicago's Metra rail authority, the defect occurs in extreme cold because the metal shrinks and the rails pull apart from each other.
To fix this, Metra will use fire to warm the metal until it expands so the rails can be connected again.
Wade Horvath saw the technique first hand.
He was riding Chicago's Union Pacific West Line when he saw the tracks burning.