Bomb disposal teams have carried out a controlled burning at a suspected bomb making factory in Leeds.
Homes were first evacuated on Alexandra Grove on 12 July
Police began evacuating about 70 houses in the area around Alexandra Grove in Hyde Park on Thursday lunchtime.
The flat is believed to have been a base used by the London bombers and is one of a number of sites police have examined in West Yorkshire.
Residents spent about three hours away from their homes while officers disposed of the substances safely.
People who live in Hyde Park were warned of the evacuation in a letter that arrived on doorsteps on Thursday morning.
In it, West Yorkshire Chief Constable Colin Cramphorn urged: "Please do not be alarmed."
He wrote: "The search of the premises has been methodical and meticulous and we are now at a point where the substances found need to be disposed of in a safe and controlled way.
"We appreciate the concern and inconvenience that recent events have caused local people, but would like to stress that public safety has been of paramount importance in the decisions we have taken."
Police have urged residents not to be alarmed
About 600 people had to leave the area around the street on 12 July, after officers found what was said to be hazardous material.
The majority were allowed home two days later after West Yorkshire Police said the material found did not represent a danger to other residents.
But sources have told the BBC that explosives made from ingredients available from high-street chemists were found in one of the homes police have searched in Leeds.
Forensic teams have been examining the property in Alexandra Grove since last week.