Fire chiefs who took charge at the Grenfell Tower fire after one hour were told "only the cladding from the outside was burning", an inquiry has heard.
Michael Dowden, a watch manager from North Kensington station, marshalled the firefighting response until around 1.50am on June 14 2017, by which point the blaze had reached the 23rd floor.
His rank meant he should only have been the incident commander for fires requiring four engines, but 25 had been called to the scene by 1.31am.
Giving evidence at the inquiry into the disaster on Wednesday, Mr Dowden said he did not believe compartmentation had necessarily failed when flames had climbed to the roof.
Compartmentation - a design feature that should ensure a blaze is kept within the flat of origin - is the basis of stay-put advice, as residents should be safe within their homes.
It is feared that the delay in ordering a full evacuation could have contributed to the death toll.
Station manager Andy Walton relieved Mr Dowden of the incident commander role and passed it on immediately to deputy assistant commissioner Andrew O'Loughlin at 1.50am.
Lead counsel to the inquiry Richard Millett QC asked of his conversation with Mr Walton: "Did you discuss compartmentation?"Mr Dowden said: "I cannot recall we did, no."
The lawyer continued: "Did you discuss the fire conditions on the building internally?" The officer said: "That is something I cannot recall."
Mr Millett then said: "Both Andy Walton and DAC O'Loughlin say in their statements they understood from you that only the cladding from the outside was burning, falling off, and the fire was only on the exterior - was that something you told them?"
He replied: "It was obvious from that time in the incident there was an external fire on the building from the way it developed so quickly, but I cannot confirm that was something I actually handed over to them."
A handwritten note drafted by Mr Dowden following the fire was shown to the hearing at Holborn Bars on his third day of evidence.
It related to the moment he requested 15 fire engines at 1.28am and said: "All my experience now gone out of the window, very daunting moment, I felt helpless."
He added on Wednesday: "There probably was moments I did feel helpless, it is a very difficult place to be as an incident commander when it is just relentless."
Asked by Mr Millett if he thought it was still safe for 999 operators to tell residents to remain inside at 1.29am, when the fire reached the roof, he said: "Everything that I had previously experienced and everything I had understood as an incident command, yes - if a building doesn't fail."
Mr Millett pressed him on whether the tower had failed by that point, to which he answered: "Not to the extent of what I know now, no."
Asked if he thought it had failed to any extent, he said: "Not to the internal, but something was happening to the external of that building."
He added: "I had not been in a position before when I ever had to make that decision or change that advice."
It also emerged that Mr Dowden failed to pass on any information about what he was seeing at Grenfell Tower to the control room, apart from that people were involved.
The earliest fire survival guidance (FSG) call had come at 1.24am and control had received 13 such calls by 1.36am, Mr Millett said.
By this point he had seen residents fleeing with blackened faces who were coughing and spluttering.
There were 170 FSG calls in progress by the time Mr Dowden relinquished his incident commander role, the inquiry was told.
He said: "The way this fire was developing, the way this was unfolding in front of me as incident commander, the way it was consuming our resources in terms of both personnel and fire appliances on the incident ground, it was very, very difficult to get that message away."
Mr Millett questioned whether the watch manager felt it was "appropriate you should have been left as incident commander until the moment you were relieved".
He answered: "I have no thoughts on that. My thoughts at that moment in time was to do the best I could as a firefighter to do the job I had been employed to do that night."
At the conclusion of his evidence, inquiry chairman Sir Martin Moore-Bick thanked Mr Dowden for speaking with "courage, candour and without shying away from the difficult questions of which, I'm afraid, there have been many".
The retired Court of Appeal judge later clarified that his comments were "borne out of courtesy for the witness" and "compassion for someone who clearly found giving evidence over three days a difficult matter", expressing surprise it had been suggested otherwise.
"I would hope that it went without saying that my remarks will not in any sense prejudice my views on the issues."
The inquiry will continue at 9.30am on Thursday.