The Parsons Green bomb packed with 400g of explosives and shrapnel could have been lethal if it had fully detonated, an expert has said.
Iraqi asylum seeker Ahmed Hassan, 18, allegedly used a "student of the year" prize to buy a key ingredient for the device on Amazon and assembled it in the kitchen of his foster home in Sunbury, Surrey.
He left it inside a bucket in a Lidl bag during the morning rush hour on September 15 last year, getting off one stop before it partially exploded, the court has heard.
CCTV footage showed 93 passengers duck for cover and scramble to get off the District line train when a fireball engulfed the carriage.
Asked what would have happened if the bomb had detonated fully, explosives expert Sarah Wilson said: "400g of TATP has the potential to cause damage to property and harm or serious harm to those in closest proximity which could potentially be lethal.
"There would have been damage to the train, the infrastructure of the train, but also harm to those in closest proximity."
On why it failed, she said: "There may be a number of reasons why it failed to function: was it made correctly? Was it wet? Other things - construction not quite right - a number of factors could influence why."
Prosecutor Alison Morgan asked: "Were all the elements necessary to make a viable explosive device present in that bucket?"
Ms Wilson replied: "Yes they were."
The court heard how she compiled a report on the bomb after taking samples of white powder before it was destroyed, confirming it was made from TATP.
Ms Wilson, who has 17 years of experience in explosives, said: "We looked at the carriage. There was no obvious explosive damage to the carriage itself. There was sooting in the ceiling."
Witnesses described seeing flames and wires sticking out of the bucket following the blast, she said.
She added: "TATP is a sensitive primary high explosive. It's very unstable and as such it's not produced for any commercial or military use.
"TATP is sensitive to a number of different stimuli - friction, impact or heat."
She said hitting or dropping it in transit could cause it to detonate.
Just one gram of TATP can cause "serious injury to people or property", she said.
She told jurors it would take at least several hours to make the 400g of TATP in the bomb plus the small amount later recovered at Hassan's home.
Ms Wilson said there was an "initial event" followed by a "slower fire" that caused damage to the device.
A "standard kitchen timer", modified to remove the buzzer, was used, she said.
She told jurors there was 2.2kg of shrapnel that had the "potential to cause serious harm". It included a mixture of knives, screwdrivers, hooks, nuts, bolts and sockets.
She said: "The addition of shrapnel or metal items in the explosive device would increase the potential of that device to cause harm or damage.
"You have the explosive which is capable of exploding but you then have a lot of small metal fragments which could also be expelled out some distance at that event."
Ms Morgan asked: "Looking at the fire wall we have seen, looking at the positioning of the device, what did you conclude happened?"
Ms Wilson replied: "My conclusion was there had been a partial explosion. Obviously this device had not fully detonated but something quite violent happened. It was likely to be a rapid burn rather than a detonation.
"The initiator mechanism, the battery, has functioned but the main charge had failed to function fully."
Traces of TATP were found in the kitchen of Hassan's home in Cavendish Road, Sunbury, including on the hob, sink and extractor fan.
After the bombing, hefled to Dover, changing his clothes, but was picked up by police the following morning, jurors have heard.
Hassan denies attempted murder and using the chemical compound TATP to cause an explosion that was likely to endanger life.