Firefighters had to break into a leisure centre to stop it being wrecked by fire after bins in a compound were thought to have been torched deliberately.
Flames had spread to the main building of Southwick Leisure Centre in Old Barn Way and were up to 40ft high when fire crews from Shoreham arrived.
A spokesman said: "Two windows at the side of the building were already blown in and we could see part of a display area had been damaged.
"We could not get in touch with a keyholder so we had to force our way in."
Crews used a sledgehammer to break through the main entrance to the two-storey building and found the ground floor clogged with smoke.
It took just under an hour to put out the fire, which started just before 4am on Saturday.
Police and fire investigators spent Saturday morning establishing the cause of the blaze.
Duty manager Mark Shackleton said the damage would cost between £7,000 and £12,000 to repair but it was hoped the centre would be open tonight or tomorrow.
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