Fifteen people have been treated for breathing difficulties after an unknown substance was sprayed inside branches of Pizza Hut, Tesco and McDonald's.
Emergency services were called to The Arcade in Upper Gornal, Dudley, shortly after 19:00 BST on Tuesday.
One person was taken to hospital, but none have suffered any lasting effects, West Midlands Police said.
A 20-year-old man has been arrested after he handed himself in at Brierley Hill police station.
West Midlands Police said it believed the substance to be a type of pepper spray and forensics experts are working to identify it.
Pizza Hut manager Philip White said he raised the alarm after himself suffering difficulties.
"I went to answer a phone, couldn't actually physically talk to the person who was taking an order, I ran around the back because my throat was just seizing up and I was like I don't know what is going on.
"I ran around the back to grab a bottle of water as soon as I came back I tried to work again, inhaled it again, then I ran around the front and was nearly throwing and it happened to two other of my colleagues as well."
West Midlands Ambulance Service said 14 people were discharged at the scene while one man was taken to Russells Hall Hospital for further assessment.
A Tesco spokesperson said its Dudley Gornal Express store was temporarily closed for a deep clean but has reopened, and staff are helping the police and fire service with their investigation.
Pizza Hut said it was working with the relevant authorities.
The McDonald's branch was closed temporarily but reopened on Wednesday morning "following an extensive clean", a spokesman said.
"We continue to assist the police with their investigation," he added.
Officers have urged anyone with information to come forward.