The head of London Fire Brigade says she would not have changed anything about the way her crews responded to the Grenfell Tower fire.
Dany Cotton told an inquiry into the blaze that they were put in an "untenable situation" and nothing could have stopped the spread of the fire.
But survivors' group Grenfell United called her comments "heartbreaking" and "disrespectful" to those who died.
The fire in west London on 14 June last year led to the deaths of 72 residents.
Ms Cotton, who was appointed in January 2017, was asked at the inquiry in central London if there was one aspect of the fire brigade's response which she would go back and change.
Survivors shook their heads as she said she "would not change anything we did on the night".
She said: "I think without exception my firefighters, my officers, and my control staff performed in a fantastic way given the incredible circumstances they were faced with.
"They were pulled into an untenable situation, a building that behaved in a way it should never have done, that put the residents' lives at risk.
"Without a shadow of a doubt, I personally was responsible for committing my firefighters to their potential death in the pursuit of rescuing as many people in that building as possible."
Ms Cotton said that even specific training in dealing with blazes involving cladding wouldn't have helped the firefighters.
She said she had never received any training on the spread of fire on cladding, but said the fire would have been deemed an "unrealistic scenario".
"I wouldn't develop a training package for a space shuttle to land in front of the Shard", she said.
"I wouldn't expect us to be developing training or a response to something that simply shouldn't happen."
But steps had been taken since, with full evacuation plans made and local authorities removing cladding, she said.
"We can no longer think that another fire like Grenfell Tower wouldn't happen, because we've seen it happen, and now we have to be able to deal with it", she added.
But Natasha Elcock, of Grenfell United, said the brigade should have learnt lessons from a previous tower block fire in Camberwell in 2009 in which six people were killed.
"To not prepare for a repeat of Lakanal House and say chances are like a space ship on the Shard is flippant and disrespectful.
"If anything, her answers suggests a culture of complacency and focus on damage limitation," she added.
"People are going to bed tonight in towers with cladding on and change needs to come fast to keep them safe."
'Like something from a disaster movie'
In a witness statement, Ms Cotton described how she first saw the blaze through her car windscreen as she arrived at Grenfell Tower at 02:49 BST.
"It just looked like something from a disaster movie. Like a hideous mixture of 'Towering Inferno' and a video I was shown in training school of a high rise fire in Sao Paulo where people jumped to escape."
The commissioner also revealed that she had wanted crews to know someone cared as they went into the tower.
She said: "I recall I actually physically went and touched some firefighters when I spoke to them, because I was not 100% convinced in my mind that everybody was going to come out of there alive.
"I wanted those firefighters to have a positive reinforced memory before they went into the building of somebody saying nice things to them, being supportive and demonstrating to them that somebody really cared."
She said she was hit by an "overwhelming anxiety" about committing firefighters to the blaze when she could not guarantee their safety.
Ms Cotton added: "People will quite rightly have questions, but for me I could not be more proud of the absolute commitment and dedication of the firefighters.
"They were clearly terrified of going into Grenfell Tower."
Ms Cotton said she had memory blanks from the night because of the "traumatic nature and sheer scale" of the incident.
She said she had undergone counselling after the fire to help improve her memory, but it had not been "terribly successful".
She also told the inquiry how she had blocked out a memory where a 6ft piece of debris almost hit her and could have killed her.
"I'm still finding it very difficult to look at visual images and have conversations about Grenfell," Ms Cotton added.