arpadveress 
Cable routing should be arranged in such a way that the cables accumulate the minimum amount of dust layers whilst remaining accessible for cleaning. Where trunking, ducts or pipes or trenches are used to accommodate cables, precautions should be taken to prevent the passage or collection of dusts in such places. Where layers of dust are liable to form on cables and impair the free circulation of air, consideration shall be given to derating the current-carrying capacity of the cables, especially if low minimum ignition temperature dusts are present.
It also means dust accumulation might be source of danger in case of gas and mist hazardous environment. Proper cleaning is a life saving effect even there.
Keep up good work!
Arpad
