Sheffield Council contractor Amey will carry out a review into its security measures after an arsonist threw flammable objects at people at its Olive Grove depot.
Police and firefighters were called to the depot on Olive Grove Road at around 6pm on Monday.
Police said the arsonist threw a flammable object at people and Amey said the intruder caused a 'small blaze’ in a staff toilet.
The man, said to be 46-year-old, was known to those he targeted, police said.
He is believed to have suffered ‘superficial injuries’ in the incident and fled before police officers and firefighters arrived.
A police helicopter was deployed in the wake of the incident to try to locate the culprit but he has not yet been tracked down.
Darren Butt, account director at Streets Ahead, Amey, said: “Thanks to the quick actions of our operatives, the fire was extinguished and fortunately none of our employees were injured.The perpetrator fled and the police are investigating.
“There is some fire damage to the building but it remans safe for use.
“In the meantime, everyone has been reminded to be extra vigilant in and around the depot and to report any suspicious activity immediately.
“Staff safety remains our utmost priority and we will review on- site access in light of this incident.
Det Con Newman Holt said: “Those involved in this incident are all thought to have known each other and we are actively looking to speak to the man involved.
“He is thought to have suffered injuries as a result of the incident and it’s really important that we find him and speak to him.”
Anyone with any information should call police on 101, quoting incident number 646 of December 10.