On September 6, NH Media explained what occurred, stating, "During filming for the MV, a smoke bomb was used for Kiseop's scene, and it caused an explosion. He suffered 2nd-degree burns, and 10 pieces of material were lodged in his body. He was transferred to a hospital in Incheon."
They later reported, "Kiseop is currently resting at home, and he will be visiting the hospital for treatment. He is stable, and he told fans that he is sorry for worrying you."
The video below shows the accident when it happened.
[WARNING: Video could be disturbing to viewers.]