im assuming your running cusions (solid tires)
are your tires black rubber? if so that may be the source of the dust
the tires wear down like pencil erasers from dead steers and other reasons
the radiator fans and exhaust could be kicking up the shavings
you can try using non-marking (white) tires that prob run about 900 bucks per machine for 5000 lb machines
also check to see if the operators are braking hard (skidding) and if they are pulling holeshots (peel out, etc) when changing directions (slow safe operation may cut down the dust)
dont forget that if this is the source and you go with nonmarking tires you will have to add a static strap or a small length of chain to the frame that drags on the ground
this discharges static buildup (unless u like little shocks and blown ECU's) as the black tires ground static thru themselves
also check the floor condition (large cracks potholes rough areas etc)