Firefighters battled to stop flames spreading from a blazing shop on a petrol station forecourt.
The Total Garage on the A286 at Birdham, near Chichester, is now closed after the incident at 6pm yesterday.
Four fire crews from Chichester, East Wittering, Selsey and Bognor managed to contain the blaze. No one was injured.
Twenty per cent of the garage shop was destroyed and the rest was damaged by heat and smoke.
A fire brigade spokeswoman said: "The fire has been investigated and this revealed an accidental cause. The garage will be closed for some time."
Firefighters were called twice in the one night to an arson hotspot in Worthing.
Youngsters set light to rubbish in Homefield Park, Chestwood Road, Worthing, last night at 9.15pm and 12.30am.
Leading Firefighter Andrew Weeks said: "When we turned up the first time last night there were groups of youths pulling bits of wood from fences and using pallets from the Co-op shop to set light to.
"We wet everything so they could not set light to it, but then they used a wheelie bin. Then it started to rain and that stopped them."
We reported last week that police have decided to increase patrols of the area because fire crews are being called to the park around five times a week.
Mr Weeks said: "It is really wasting our time and it is damaging the skate park."
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