Fire crews tackled a blaze at an industrial unit in Andreas for three hours on Tuesday evening.
The unit, on the Andreas Airfield site, was being used for storage by a building firm.
Efforts to extinguish the fire were hampered by gas canisters stored inside, which fed the flames.
It was also suspected there was asbestos in the roof, which becomes even more hazardous once alight.
It took the crews from Ramsey and Kirk Michael until 8pm to put the fire out.
The Isle of Man Fire and Rescue Service believes the blaze was caused by a bonfire that was left smouldering, and unattended, close to the building.
It spread via vegetation.
Details of the incident were issued today (Thursday).