On Thursday June 22, 1995 the Eastern Region of the National Cave Rescue Commission was holding a Mock Cave Rescue training exercise as part of the 1995 Weeklong. At approximately 1:30 p.m. Doug Moore (24) was walking through the cave when he hit his head while wearing a helmet. The impact was very hard and immediately a throbbing pain started. It continued for over five minutes so he decided that he needed to exit the cave and asked someone to exit the cave with him. This was mainly due to the severity of the pain.
After exiting the cave approximately 30 minutes after the incident he approached Dr. Sam Chewning about medication and to report the incident. Dr. Chewning gave some medication which did little to relieve the pain. The pain continued for approximately 12 more hours after the incident.
Doug Moore, accident report, 03/24/96.
In short, even with a helmet on you can wack your head severely. If I hadn't had a helmet on I would probably have had a severe concussion.