Hi,
Funny enough, was reading the cleaning and maintenance magazine, where there is a large 4 page advert on Victor products, and they do a battery powered backpack vacuum.
Only seems to have half of the power compared to the electric ones.....but it is battery!!
However, if you get a powered one, i'm sure that as long as you have a couple of "Danger, cleaning in progress" signs, you should be ok. Don't forget to incorporate this in your Health and Safety pack.....
Happy hunting
Regards
Tim