LONDON: Oozing rucksacks, harmless puffs of smoke and the failure of the latest apparent attempted suicide bombings in London suggest a link between this week’s attacks and the July 7 bombings, experts said on Friday. Explosives specialists said the four bombs which apparently failed to explode on Underground subway trains and a double-decker bus on Thursday bore similarities to the type of Al Qaeda-style devices used in the suicide attacks earlier this month.

Witnesses spoke of seeing a lard-like substance oozing from one of the would-be bombers’ backpacks after it failed to go off, suggesting the presence of an explosive mixture such as acetone peroxide which was used on July 7.

That substance — made from household items like sulphuric acid, hydrogen peroxide and acetone — deteriorates over time and becomes harmless if it passes its use-by date.

“If the bombers from July 7 and yesterday all loaded their rucksacks together two-and-a-half weeks ago, then you might expect a substantial amount of the explosive to have disappeared by this week,” said chemist Andrea Sella of University College London.

“It sublimates away like camphor. Sublimation is the evaporation of a solid, as molecules leave a solid to go into the gas phase, as with camphor mothballs.”

She said explosives manufacturers spent a lot of time refining the size of the particles in the mixture, which determines its explosive power.

“How coarse or fine your mixture is helps determine whether it will explode, burn or just go ‘phut’,” she said.

Abisha Moyo, a Zimbabwe-born business analyst who was on a subway train near Shepherd’s Bush station in west London when the incident happened on Thursday at lunchtime, described hearing a bang like a pistol shot and noticing a man lying on the floor with a rucksack on his back.

“He had his eyes shut and there was a puff of smoke coming from the bag,” he was quoted as saying by the Daily Mail.

“The rucksack was ripped at the bottom, with some sort of muslin showing and some gooey lard coming out of it. I could see what looked like a pressurized canister or tube and there was a strong smell of vinegar,” he said.

Andy Oppenheimer, of Jane’s Information Group which analyses security and defence issues, said acetone peroxide could have been used in both attacks and might have come from the ‘same batch’.

“If this is the same material in both attacks, it can deteriorate and may have lost its function,” he said.

“It is an explosive that has to be used quickly after it is made. There is a possibility that that is what has happened here — rather than the detonators failing it is the actual explosive mixture that has failed.”

He said acetone peroxide could lose its explosive capacity within ‘a few days’.

“They probably have tried to rush to make some more devices and get them deployed as quickly as possible,” he said.

Media reports have said police have already found similarities between the explosives used in both London attacks, but this has not been confirmed by the police themselves.

Metropolitan Police chief Ian Blair said the wealth of forensic evidence from the latest attacks ‘may represent a significant breakthrough’ in the massive investigation into terrorist groups in Britain.

British authorities have listed the attacks two weeks ago as being the likely work of Al Qaeda network. But Ian Blair has refused to make a definitive link between those attacks and the latest incidents. —AFP