American Medical Response says they responded to at least 20 incidents due to the heat at McKay’s 50th anniversary celebration.

AMR says two of those affected were taken to the hospital and 15 were treated on the scene.

Knoxville Fire Department’s Mark Wilbanks says traffic issues on Papermill Drive, Weisgarber Road, Kingston Pike and other roadways affected their ability to dispatch crews. Willbanks told WVLT News that the department and McKay’s decided to end the event early. He also called the situation a “mass casualty incident,” citing the number of people affected and responders’ limited resources.

In honor of the franchise’s 50th birthday, McKay’s set up The Ultimate McKay’s Road Trip. The used bookstore is challenging fans to travel to every McKay’s location in one day to earn prizes.

The monumental day for McKay’s ends on a sour note after the Knoxville location was shut down due to severe heat and weather concerns. Again, at least 20 heat-related incidents were reported at the Knoxville location, the road trip challenge involved traveling to all five McKay’s locations in one day to earn various prizes including up to $800 in free credit. Those who showed up at the Knoxville location and turned away received credit for visiting the store.