Two firefighters who died at a former RAF base in Bicester have been named as Jennie Logan, 30, and Martyn Sadler, 38.
David Chester, 57, who ran a construction business from the site, was also killed in the fire on Thursday evening.
London Fire Commissioner Andy Roe said Mr Sadler was on call for Oxfordshire Fire and Rescue Service (OFRS), but was part of blue watch in Ealing, west London, where he was a leading firefighter/sub-officer.
He also confirmed Ms Logan worked for the Oxfordshire service.
The ex-RAF base in the Oxfordshire town is home to Bicester Motion, a business park that includes classic car restoration firms.
Its boss Daniel Geoghegan said Mr Chester had run a business, Chesters & Sons, on the site for 12 years.
It called him a "part of the fabric of our estate and a friend to us all".
"Our whole community used to say that 'Dave always had our back'. Yesterday, he was doing just that - the epitome of his selfless spirit," said a statement.
He added: "We will cherish you Dave and you will be sorely missed, and we send our utmost love to Sue, Jordan and Riley."
Mr Geoghegan also sent "heartfelt condolences" to the firefighters' families and said Ms Logan and Mr Sadler had "bravely tackled the scene".
"No words can ever make up for what has happened, but they are all very much in our hearts," he said.
Two other firefighters sustained serious injuries in the blaze and were taken to hospital.
Chief Fire Officer Rob MacDougall, from Oxfordshire Fire Service, announced the deaths earlier on Friday.
"It is with a very heavy heart that we today report the loss of two of our firefighters. Families have been informed and are being supported," he said.
"Our thoughts are with them at this most difficult of times and we ask for privacy to be respected."
He appeared to hold back tears as he talked about how "proud and grateful" he was.
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Emergency services were called to the scene at 6.39pm on Thursday, with 10 crews attending.
Footage on social media showed plumes of black smoke and flames swallowing the large building.
Kieran McGurk, who lives opposite the site, said he heard "multiple explosions" and "loud bangs". Another resident - who gave her name only as Ellie - said she "heard loads of pops and crackles and bangs".
Assistant Chief Constable Tim Metcalfe said Thames Valley Police were investigating but the fire wasn't currently being treated as a criminal matter.
Prime Minister Sir Keir Starmer said the deaths were "devastating news" and he hoped "those in hospital make a full and swift recovery".
Tory leader Kemi Badenoch said her "heart goes out to the families of those people who have lost their lives and those who are still on the front line".
(c) Sky News 2025: Police name firefighters and business owner killed at former RAF base in Bicester