Arsonists who torched two cars on an industrial estate destroyed three out of the nine units.
Wallingford police are investigating the fire at Queenford Farm, Dorchester, which happened on Friday evening.
No-one was put out of work -- people from the three units moved into others on the site.
Estate owner Ian Read said: "One of the cars was right up against one of the units and set it alight. There was a very great deal of damage.
"Fortunately no-one was hurt -- the site was deserted at the time."
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