The fire at the 2012 Olympics site, which threw up a huge plume of smoke over London, was an accident.
The blaze at a warehouse in Hackney Wick, east London, on 12 November began by sparks from an oxy-acetylene torch setting material alight.
The Olympic Delivery Authority (ODA) said workmen had been cutting steel piping during demolition work in the Olympic Park site.
Similar work has been suspended while procedures are reviewed.
The all-clear was also given over fears that asbestos may have been released in to the air.
Professor Virginia Murray, of the Health Protection Agency, said: "In terms of public health surveillance, no adverse health effects have been reported so far."
Smoke plumes 200ft high could be seen 20 miles away and 75 firefighters tackled the fire on the edge of the Olympic Park. No one was hurt.