Owner William Grieve, whose father Walter established the business, rushed to the fire from his home in Birtley a few miles away after a friend called at about 12.10am yesterday to tell him about the blaze.
He said: "We arrived there and it was just chaos. It is awful having to just stand there and watch - you feel so helpless.
"It is just absolutely devastating to watch your whole life go up in front of you.
"The flames were coming out of the building and you could feel the heat as you got closer. I have been working there for the last 35 years, since I was 15, and there is stuff we will never be able to replace."
Among items destroyed in the fire were a BMW car belonging to a customer and a computer used for MOTs.
Much of the money that is generated by the business is used to fund the flourishing motor racing career of Mr Grieve's son, Christopher.
Featured just last week in The Journal, the 23-year-old is current champion of the Legends National Championship, in which he drives a Chevrolet Sedan.
Fortunately the racing car is not kept at the garage, although a Ford Fiesta modified by Chris at a cost of thousands of pounds is thought to be damaged.
Because of the explosive canisters, which contained acetylene used for welding, the family have not been able to visit the garage as police and fire crews have cordoned off the area and shut the Barrasford to Wark road for 24 hours while they are made safe.
Despite the fire, which Walter Grieve, 75, described as a disaster, William said the consequences could have been worse. He said: "You have got to be thankful that there was no one inside and no one was hurt.
"The fire crews did a fantastic job and we will just get on with it - the message to our customers is that we will be carrying on."
A cordon was thrown around the premises 200 metres away and special equipment has been used to cool the cylinders.
A fire service spokesman said: "The cordon will remain in place for 24 hours and Northumberland Fire and Rescue Service continue to have one appliance and crew working at the scene."
A police spokesman said: "At this stage the fire is not being treated as suspicious."
Written by The Journal - Newcastle-upon-Tyne