The fire was set in or near "plastic" baths and the power of flames then caused the over-heating and explosion of gas cylinder(s) stored in metal cage nearby on site.
Bedfordshire and Luton Fire and Rescue Service received multiple 999 calls from 04.11 onwards on Monday 17th May.
On arrival crews found stock on fire in the yard of the building. Four fire appliances (Luton, Stopsley and Dunstable) attended and the fire was put out by 05.30.
Fire crews stopped the fire spreading to the building itself - which was NOT involved in fire.