CHICAGO (CBS) — All Southwest Airlines flights in and out of Chicago were cancelled Sunday due to a lack of deicing fluid.

Deicing fluid is a mixture sprayed to remove ice and snow on aircrafts.

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“Southwest Airlines Operational Planners continue to carefully track winter weather moving through Chicago [Midway]. Throughout the storms, we’ve actively worked to manage our glycol levels, but due to the severity of the winter weather, Southwest has proactively canceled about 220 flights,” the airline state in a statement. “We have paused our service for the remainder of the day for the safety of our customers and crews.”

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Southwest said they will work with their customers regarding their travel plans and are offering refunds or flight vouchers.

Midway International Airport also cancelled more then 250 flights Sunday due to “winter operational issues.”

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Individual airlines are responsible for deicing operations, not the airport itself.