Firefighters were scrambled to a fish and chip shop in Woodford Green after a fire broke out.
Six fire engines and around 40 firefighters were rushed the blaze in High Road just after 12.50pm on Thursday.
Part of the shop was damaged and the ducting - which runs from the ground to the second floor of the building - was completely destroyed.
One man suffered from smoke inhalation and was treated on scene by paramedics.
A London Fire Brigade spokesperson said: "This fire spread inside the ducting.
"We'd like to remind restaurant and takeaway owners to ensure they don't have dirty ducting. If you don't clean the ducting in your extraction system regularly, you're at a greater risk of ducting fires.
"You should also make sure you keep the hob, cooker hood and extractor fan clean too – built up fat and grease can ignite and cause a fire."
The fire was under control by 2.03pm.
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