The explosive used by the alleged 21 July bombers was as powerful as TNT or gelignite, a jury has been told.
The explosive was in a container covered with nails, the jury heard
Forensics expert Claire McGavigan said that, had one of the devices exploded, lethal shrapnel would have travelled at "hundreds of metres a second".
People could have died, been seriously injured or lost limbs, she told Woolwich Crown Court.
Six men deny conspiracy to murder and conspiracy to cause explosions on London's transport network in 2005.
They are Manfo Asiedu, Muktar Ibrahim, Hussein Osman, Yassin Omar, Ramzi Mohammed and Adel Yahya.
The jury has heard how none of the four bombs set off in three Tube trains and a bus exploded properly.
Mr Mohammed is alleged to have tried to detonate a rucksack bomb on a Northern Line train between Stockwell and Oval.
Ms McGavigan, a senior case officer at the Forensics Explosives Laboratory in Kent, tested samples from his bag.
"It was comparable to the gelignite and the TNT used in the same tests. These are both high explosives as well," she said.
"Any fragment travelling at that speed and possibly very hot is very dangerous and can obviously embed itself in a person and cause serious injury.
"There would be serious damage to the train itself, there would be serious injuries, quite possibly death to people in the area at the time."
On the day of the alleged attempted attacks, Ms McGavigan examined the remains of Mr Mohammed's alleged bomb on the floor of the Tube carriage.
It had a "strong chemical smell, a bit like bleach", was sticky and made her eyes sting when she tried to scoop it up, she said.
She also told the court that she thought the home-made device had not gone off because of a problem with the detonator.
"It appears that the most likely reason was that the initiator containing the TATP [triacetone triperoxide - an explosive sometimes used in detonators] wasn't actually powerful enough to set off the main charge in this particular case," she said.
Smoking and burning
The explosive was placed in a plastic container with shrapnel such as nails and screws taped to the outside, the court heard.
Earlier the jury was told that a sample of the explosive charge from Mr Mohammed's rucksack started to smoke and burn through layers of forensic packaging five days after the attempted attacks.
Ms McGavigan said she had smelt burning the moment she went into a separate building to the main laboratory on 26 July 2005, where the sample was kept.
The pale yellow gel-like mixture was being stored in special anti-static bags, placed in water and then in plastic boxes, the court heard.
She told the jury that she and the principal forensic investigator had hosed down the outside of the bag.
"Some of the material had burnt and was black and charred. It burnt through three layers of packaging and left a hole," she said.