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Dover crews tackled a suspected arson attack in Tower Hamlets Street in the early hours of this morning.
Firefighters were called at 4.10am and spent an hour in an alleyway, where an old mattress was on fire, and leaning against a building.
Neighbouring residents were unaware of the fire at first, as their fire alarm didn't alert them to the incident.
This has lead to a recommendation from the crews, urging people to make sure their fire alarms are active at all times.
Watch manager, Tony Scott, said: "We recommend that smoke alarms are tested once a week to make sure they are working.
"Its all good having them, but they need to be working."
The fascia of the building was damaged.
No one was injured.