Nobody could have survived in the stairwell of Grenfell Tower by 1.57am without breathing equipment, according to a firefighter who almost died that night.
Christopher Secrett, a crew manager from North Kensington red watch, found himself low on oxygen during a mission to rescue a 12-year-old girl from the 20th floor.
He collapsed from exhaustion in the staircase - the building's only escape route - and considered contacting his mother out of fear he would not survive the descent.
The firefighter, who burst into tears while giving evidence at the inquiry into the fire, was thanked by chairman Sir Martin Moore-Bick for his bravery on June 14 last year.
He said: "I would just like to say that I've been very impressed listening to your account this morning and the degree of bravery you demonstrated on that night and complete disregard, it seems to me, for your personal safety."
Mr Secrett had joined firefighters David Badillo and Chris Dorgu on a rescue effort to Flat 176 - the family home of a schoolgirl reported trapped, Jessica Urbano Ramirez.
They arrived to find the 20th-floor flat smoke-logged and the little girl nowhere to be seen.
He told a hearing at Holborn Bars that air only started to clear "fairly close" to the second floor, where the bridgehead, or safe-air space, was located.
Lead counsel to the inquiry Richard Millett QC asked if at any point he would not have needed breathing apparatus, to which he replied: "No, absolutely not."
Pressed on the air conditions at that time, he said: "On the bridgehead they were fine, but there is no way myself or anyone else could have survived without breathing apparatus on at that time I was on the stairs."
He arrived there at 1.57am, according to Mr Millett, who asked him whether "essentially the stairway was unusable".
"Yes, definitely," replied Mr Secrett, confirming this was true from the 20th floor down to the second.
His account suggests the difficulties firefighters would have faced carrying out a full evacuation of Grenfell Tower, due to the speed of the fire's spread.
Fire commanders have been criticised for failing to abandon the standard stay-put advice to residents until 2.47am, nearly two hours after the fire began.
Mr Secrett's evidence also laid bare the communication problems which plagued firefighting crews that night.
A 999 call operator who spent 55 minutes on the phone to Jessica knew she had left Flat 176 to seek shelter on the 23rd floor, but this fact had not been passed on to her rescue team.
Mr Secrett said neither he nor his colleagues were receiving any radio traffic on the 20th floor, despite attempting to contact superiors on the second floor.
He took a long pause before setting out the communication failings, explaining he had "a little wave" of emotion.
He continued: "To a point we had a complete disconnection from the outside world."
Mr Secrett and Mr Badillo took the risky decision to search the 20th-floor flat without any water as "time was of the essence", during which time his warning whistle for oxygen sounded.
"In normal circumstances if your whistle goes off you've got 12 minutes of air remaining at a rate of 50 litres per minute. I don't know what my breathing rate was but I imagine it was a lot more than that," he told the hearing.
"It all started, kind of started, going wrong for us all at once - we couldn't find who we were looking for, my air was running out and the temperature raise, it was like, 'Let's get out of here'.
"I remember having this huge wave of, 'We've come too high', my whistle was going ... at that point I was very unsure whether we were going to get out or not.
"We had no way of communicating that back to the bridgehead."
The whole temperature of the 20th floor "spiked quite quickly", Mr Secrett said, agreeing it appeared they "all were" suffering from the effects of heat stress.
The team entered the stairwell to thick smoke, where conditions were "definitely worse".
"My legs were wobbly from exhaustion. I tripped a few times and at one point we lost Chris Dorgu, so I crawled to the corner of the lobby and asked Dave to call out for him because I didn't have the energy to."
At this time, hope of a safe escape had started to fade and Mr Secrett considered texting his mother, but decided against it. They were then pulled to safety when Mr Dorgu reappeared.
Earlier, the emotional fragility afflicting many firefighters who attended Grenfell Tower was again demonstrated when Mr Secrett broke down.
He began pinching his eyes tightly, sobbing uncontrollably, when Mr Millett asked him to recall the first time he realised the blaze almost engulfed the block.
The firefighter had been inside at the bridgehead when the original kitchen fire was being extinguished, at first not realising fire had spread up the building's exterior.
Several firefighters, including senior officers, have broken down during their evidence, prompting the inquiry to offer them breaks at least once an hour.