Customer asked me if i could clean high internal ducting in a large supermarket , about 40ft high in places , round ducting with visible [ to me looks like dust ] dirt , unsure of best way to go about it ,or to quote . Got to be compliant with H&S [ that means no ladders ] and to keep cost down, if i can come in with a good quote and method could be many more sites, i'm a wfp w/c and i dont know why he's asking me but i'm not turning down good money if i can help it, anyone with any ideas / methods exp ?