A Dumfries and Galloway Police spokesman said:
“The causes of the fires are being investigated. We are anxious for anyone with information to come forward so that whoever is responsible can be apprehended.”
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The historic event always takes place on the last Friday in July.
Early enquiries suggest the men may have taken the drug Blue Valium. Two of them remain in hospital with breathing problems.
More than 8,000 people are expected to attend over the three day event, which starts at 7pm tonight.