Petrol was sprayed over a member of staff during a raid at a bookmakers in Doncaster.
South Yorkshire Police said a robber entered Mark Jarvis Bookmakers in Bentley carrying a plastic bottle containing petrol.
He sprayed it over a member of staff and made threats before escaping with cash from the till.
The robber, who struck at the High Street-based bookmakers at 5.40pm on Tuesday, July 4, was wearing a black balaclava.
He was also wearing a grey hooded coat, blue jeans and black gloves.
He fled in the direction of Millgate.
Detective Sergeant Debra Renwick said: “Thankfully no one was hurt in the incident, however the victims were left shaken and I would urge any witnesses who may be able to assist with our investigation, to please contact us.”
Anyone with information should call South Yorkshire Police on 101 or Crimestoppers on 0800 555 111.