One building was badly damaged by the fire
Gas canisters went off "like bombs" during a "serious" fire at an industrial estate.
Residents living near the site were advised to keep windows and doors closed while more than 40 firefighters fought the flames from about 17:45 GMT on Wednesday.
A plumbing supplier and an industrial unit on the Haigh Estate in Ross-on-Wye were damaged in the blaze.
Initially, firefighters thought a wood-burning stove could be the cause.
By Thursday afternoon, it had been ruled out.
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The fire was extinguished at about 03:10, a spokesman said. The full extent of damage at Alton Road is unknown.
The Environment Agency said it worked with the fire service to protect the community
Resident Alan Tandy called it a "severe fire" and praised the bravery of firefighters who worked as gas canisters went "off like little bombs".
He said: "There's a great big cylinder which would probably have removed most of the buildings on the estate if it had gone up, so they are brave guys."
The fire was extinguished at about 03:00 GMT
Residents living near the site were advised to keep windows and doors closed
