Four fire engines and around 25 firefighters were called to an incident at a mixed-use commercial and residential block on Tower Brigade Road near Tower Bridge.
Chemicals were mixed in the basement swimming pool area. Firefighters carried out a sweep of the property and confirmed elevated readings of chemical substances on arrival. One man was treated on scene by London Ambulance Service crews.
Crews evacuated around 70 people from the building and a 50-metre cordon was put in place as a precaution. Firefighters used specialist equipment to contain the spill of chemicals and ventilated the property.
A London Fire Brigade spokesperson said: “Always follow the instructions for cleaning products and chemicals carefully and don’t be tempted to mix them as it could produce hazardous fumes.
“Make sure you also wear gloves when using cleaning products and always keep them securely sealed and out of the reach of children.”
The Brigade was called at 1018 and the incident was over for firefighters by 1502. Fire crews from Dockhead, Dowgate, Whitechapel and Bethnal Green fire stations attended the scene.