When propping a C172 by hand due to a dead battery; the pilot failed to set the parking brake and was unable to restrain it after the engine started. Damage was limited to the aircraft and the T-hangar which arrested it.

Narrative

The battery on the airplane was dead; so I was attempting to start it by hand-propping it. I have received instruction from a CFI in proper procedures. I set the parking brake; but did not chock the wheels. The engine would not start after numerous attempts; so I decided to put the plane back in the hangar. I released the parking brake in preparation for the push-back. Then; without thinking; I decided to make one more attempt at starting the engine. This time; it started right away and began taxiing on its own. It traveled about 100 feet and ran into a T-hangar. The propeller was bent and the left wing tip was dented. From my inspection; it appears that only one rib was damaged. There was also a slight buckle in the skin of that wing about halfway from the fuselage to the wing tip. My understanding is that this is not a reportable accident under NTSB rules since (1) I never boarded the aircraft; (2) there was no serious injury involved (3) damage to the hangar was substantially less than $25;000; and (4) damage to the aircraft was not substantial.