From our Deicing Manual:
Type I fluids are used for both deicing and anti-icing. It is primarily used heated as a deicing fluid. It has limited effectiveness when used for anti-icing. Type I fluids which use ethylene glycol as a freezing point depressant may be used undiluted for anti-icing. Type I fluids which use propylene glycol as a freezing point depressant must not be used stronger than 60 percent deicer.