The police watchdog is investigating whether a Taser electric stun gun ignited a flammable liquid which caused a man to be fatally burned.
Andrew Pimlott, 32, died five days after a liquid he was covered in caught fire after officers were called to a house in Plymouth on 18 April.
The Independent Police Complaints Commission (IPCC) said it was investigating why the weapon was used.
Mr Pimlott's family have paid tribute to their "fantastic son".
Two officers from Devon and Cornwall Police were called to the house at about 21:00 BST on 18 April after reports about a man with a can of flammable liquid were made by a member of the public.
The IPCC confirmed a Taser, which delivers a 50,000-volt electrical charge into targets to incapacitate them, was fired during the incident.
After he was burned, Mr Pimlott was taken to hospital in Plymouth before being transferred to Bristol's Frenchay Hospital. He died on 23 April.
The IPCC said its investigation would focus on the circumstances leading to his death.
Commissioner Sarah Green said: "Our investigation will be looking at what information was known to the officers attending the scene, the officer's rationale for discharging a Taser on a person known to be doused in flammable liquid; whether the discharge of the Taser caused the fuel to ignite; and we will look at training and policies."
Deputy Chief Constable Simon Chesterman of the Association of Chief Police Officers said officers receive "very good training" in Taser use.
Speaking generally about Taser use, he said there were "always going to be cases" where an officer's judgement was mistaken, but in the majority of cases it was justified.
Alternatives, such as using a baton or a police dog, often resulted in worse injuries than being Tasered, he added.
A solicitor who specialises in cases where people have been Tasered said there were very few circumstances in which use of the device was justified.
"They should be used as an alternative to the firearm; so if there is a life-threatening incident, either to a member of the public or to the police, and the police feel that the only way to stop the life-threatening incident would be to Taser someone, in that scenario I would say to use the Taser," solicitor Sophie Khan said.
"But anything outside of that, I would say is unlawful and excessive use of force, and in this scenario has led to a death."
In their tributes, Mr Pimlott's family said he was a "fantastic son", as well as a "dear brother and uncle".
The tributes added: "We are going to miss you so much and you will never be far from all our thoughts.
"You will always hold a place in all our hearts."
Devon and Cornwall Police said it was co-operating fully with the IPCC.