Paul
Leaving machines over night, make sure you have had them PAT tested and have a copies on file, I would also recommend an rcd with them, the same applies if you need to use extension cables, and if you have to use them if the wound up type make sure you leave it un-wound when in use.
Have a little storey re extension cables a FF person was dealing with a flood left de-hums over night got a call you know the flood you are dealing with, well they now have a fire, a true story.
Len