An old mattress and rubbish were set on fire in a stairwell in a block of flats in Sheffield.
Firefighters were alerted to the blaze on Washington Road, Sharrow, at 7.40pm yesterday.
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Flames did not spread to any of the flats.
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Arsonists in Sheffield were also responsible for setting fire to two wheelie bins on Spring Close View, Gleadless Valley; a motorbike torched on Batemoor Road, Batemoor and a Suzuki Alto found alight on Chaucer Road, Parson Cross.
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In Barnsley, a Saab was fired on Lang Avenue, Lundwood; an Audi A3 was torched on Summer Street and a Vauxhall Insignia was found burning on Hound Hill, Worsbrough.
A Ford Transit van was set on fire on Lodge Lane, Braithwaite, Doncaster and a Toyota Land Cruiser was torched on Addison Road, Maltby, Rotherham
Anyone with information should call South Yorkshire Police on 101.