Police and firefighters were scrambled to Doncaster Royal Infirmary yesterday after three men rushed into the emergency department claiming an unknown substance had been thrown at them in the Thorne Road area.
Shocked bystanders initially feared they were witnessing the aftermath of an acid attack.
But all three men were tested and police, who were called at around 1.50pm, said no traces of a harmful substance or chemical were found.
When officers searched a vehicle in the hospital car park with smashed windows, however, they discovered a variety of weapons including knives and a hammer.
The weapons were seized, and two men aged 21 and a third aged 17 were subsequently arrested on suspicion of possessing offensive weapons.
All three men were released under investigation while police conduct further enquiries.
Anyone with information about yesterday's events or concerns about the use of weapons where they live is asked to call police on 101 or Crimestoppers, anonymously, on 0800 555 111.