A firefighter was repeatedly refused permission to access King's Cross Tube station despite choking passengers emerging from the smoke-filled tunnel, the 7 July inquest has heard.
Andrew Shaw said his senior officer told him to wait until a second crew arrived at the scene.
Poor radio communication, because of heavy radio traffic, was also frustrating for the firefighters.
Germaine Lindsay killed 26 people with a bomb on the Tube on 7 July 2005.
His attack, on a southbound Piccadilly Line train between King's Cross and Russell Square, was the most deadly of four co-ordinated attacks on the London transport network, which killed a total of 52 people.
A fire crew which arrived at King's Cross station saw an increasing number of passengers emerge from the platforms, with a worsening array of injuries but were ordered to wait for back-up.
'A bit useless'
Mr Shaw said: "There's obviously smoke down there and there's obviously people that need help.
"You kind of feel a bit useless when you're standing around not doing much. So, yes, you want to assess the situation and you want to just continue with the job."
He and a colleague were eventually allowed to go to the bottom of the escalator, but then also ventured further onto the platforms.
He saw one "visibly distressed" British Transport Police officer who spoke of the loss of life in the bombed Tube and said there had been an explosion.
Mr Shaw said it was only when a second appliance arrived - at 0942 BST, almost an hour after the bomb was detonated - that he and his colleague were allowed to go all the way in to the tunnel.
The inquest heard radio communications were problematic, possibly because of being in a built-up area where there could be "blind spots", plus the volume of radio traffic that day.
Combined with protocol preventing him going to the tunnel, Mr Shaw agreed with the suggestion from inquest counsel Hugo Keith QC that it was all "deeply unsatisfactory".
Waiting for back-up
Once in the tunnel, he stayed at the scene until all the living casualties had been removed but described the process of moving the deceased and carrying people out of the tunnel as one of the worst jobs he had ever had to do.
Inquests at the Royal Courts of Justice are examining the deaths of the 52 people who were killed by suicide bombers on three Tube trains and a bus.
Adam Colebrook-Taylor, of the London Fire Brigade, who was in charge of Soho station on 7 July, explained the process of committing crews.
"Protocol is that we don't commit crews when you're really with bare minimum.
"The reason behind that is, if you send your only two crew down to an incident, whether it be sub-surface, whether it be a high rise, you've got no means of, if they got into trouble, of rescuing them.
"So it's always laid down that, you know, you have to wait for a second crew."
The inquests also heard how the rescue effort was hampered by confused instructions which meant some firefighters were dispatched to Euston Square rather than to King's Cross.
Mr Colebrook-Taylor's fire engine was "still being committed and deployed to Euston Square at 09.39", said Christopher Coltart, representing seven of the victims' families.
"But for the fact that one of his officers had spoken by mobile phone with [another officer] on the appliance which was already at King's Cross, that's where they would have gone, and it was only by that happy chance, that the two officers had spoken to each other, that Mr Colebrook-Taylor knew to attend at King's Cross."
Questioning Mr Shaw about the Euston Square mix-up, he said: "In the context of what was happening that morning, that was a disaster, wasn't it, frankly?"
Mr Shaw replied: "It was unfortunate, yes."