On December 26, 2005, at approximately 1635 Pacific standard time, a McDonnell Douglas MD-83, N979AS, was substantially damaged when the airplane experienced a rapid cabin depressurization during climb out from Seattle, Washington. The airline transport pilot captain and first officer, the three flight crew members, and the 137 passengers were not injured. Alaska Airlines Inc. was operating the airplane under Title 14 CFR Part 121, as flight number 536. Visual meteorological conditions prevailed for the commercial cross-country flight that originated approximately 30 minutes before the accident. The flight was on an IFR clearance with a destination of Burbank, California. The captain said that the airplane arrived late into Seattle, from its previous flight, and the new flight crew was waiting at the gate. After the airplane was chocked and the engines were shut down, the first officer immediately performed his preflight inspection. A new (approximately one week on the job) ground baggage handler, who was driving a tug towing a train of baggage carts, said that he waited for a belt loader to be correctly positioned on the right side at the middle cargo door of the airplane. He said that he approached the airplane from aft to forward, but had to maneuver around another train of carts to get close to the belt loader. Once in position, he said the front of his tug was 4 to 5 feet away from the airplane. After loading the carts with baggage, he attempted to drive away. He said that he turned the tug's wheels as far as possible. He stated, "I was hoping to make it out, but I felt my tug going against something. I immediately set my foot on the brakes and glanced at the body [in moderate rain] of the aircraft to see if there was any damage. It was a quick glance and I did not see any damage." He said two other ground personnel came to assist him in maneuvering his tug away from the airplane. He did not report the incident to anyone. The pilot said that the takeoff was normal. During the climb out, at approximately 26,000 feet, they heard a loud bang, and the cabin depressurized. He said that they put their oxygen masks on, and coordinated a descent to a lower altitude with Seattle Center. An uneventful landing was performed at Seattle-Tacoma International Airport, Seattle, Washington. Post landing examination of the fuselage revealed a 12 by 6 inch hole between the middle and forward cargo doors on the right side of the airplane. After the occurrence, the ground baggage handler confessed that he had "grazed the airplane" with a tug, while attempting to depart the vicinity of the airplane.