As recommended above bare steel (a dry chain or ding in the paint) can be a problem when the humidity is over 45-50%. In our maintenance warehouses we were careful to keep them closed up in the spring and fall when we would see large swings in temperature between day and night. Cold air ingress at night cools the metal and the humid daytime temps rise quickly resulting condensation on the bare metal. Just like a cool beer can on a warm humid day.