Police were called to Lee Street in Haymarket shortly after 1.30pm on Friday where they attended to a male, believed to be in his thirties.
Police spent between eight to 10 minutes trying to negotiate with the "deeply disturbed and upset individual" outside the building before he doused himself in petrol, Detective Superintendent David Donohue said.
While police would not confirm what the man's concerns were they did say his actions were in protest and that "he was a person who suffered mental illness".
The man, who was known to authorities prior to the incident, suffered superficial burns to his thighs.
He was treated at the scene before being taken to hospital for a physical and mental health assessment.
Detective Superintendant Donohue said the quick actions of police officers mitigated the injuries sustained by the man.
"This incident demonstrates the brave police officers on a daily basis across this state responding to very difficult self-harm jobs from mental health patients," he said.
"On each occassion our endeavour is to resolve these matters peacefully."
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