Fifty people evacuated from a block of flats on Cottons Approach in Romford yesterday evening, while firefighters investigated a suspected carbon monoxide leak.
A woman and two girls who left the building before the arrival of the Brigade were treated at the scene by the London Ambulance Service.
Firefighters used detection and monitoring equipment to sweep a five roomed flat on the second floor, but no elevated readings were found. The building was ventilated as a precaution.
Two fire engines from Romford and Harold Hill fire stations attended the incident.
The Brigade was called at 2017 and the incident was over at 2258.