Denver’s largest carrier, United Airlines, canceled about 90 departures and arrivals on Thursday.

About 40 planes were damaged by hail that pummeled the airport for about 15 minutes Wednesday night as severe thunderstorms moved through the Denver area.

Airport spokeswoman Laura Coale says all damaged planes must be evaluated, which has slowed operations. She says some planes have been taken out of service because of damage, but it wasn’t immediately clear how many.

United is waiving fees for passengers flying through Denver and Colorado Springs who need to change their flights.