This scene greeted me as I first observed a batch of these impellers for inland waterway vessels reach "knock-out" in the lost-wax foundry - movie of hideous dust emission.
What's happening here is that the forward exhaust of the smaller chisel / descaler tool, which would normally clear the work area of released debris in a desirable way, is now working against you. The released refractory is fine, and in the recess of the casting, it is all ejected backwards all over the operator.
Here is the answer in action - movie showing zero dust emission.
How it works is that the pneumatic breaker exhausts backwards through the base of the handle - away from the casting being knocked-out. And the length of the big chisel keeps the exhaust and other air-movement from the juddering breaker away from where the chisel is breaking up the refractory. The released refractory stays in place and the Operator stops every now and again to tip over the casting and pour out the released refractory.
It might be counter-intuitive to apply a big breaker to a product casting. However, big pneumatic breakers are very controllable with a proportional operating trigger - big pussy-cats really. And their size and weight to power make them accurate to control.
Furthermore... The most accurate power tool regulation available is using a compressed-air tool supplied through a pressure regulator (reducing-valve). And the airline connection to the air-main has a regulator already in place. With a slightly blunted chisel, you can regulate the supplied air pressure so that the chisel cannot ever mark the product casting.
As it happens, this isn't necessary once the Operator has got used to using the pneumatic breaker for this knocking-out operation.
Sometimes metal has leaked through the shell into cavities in the ceramic backing. Applying the pneumatic breaker to these lumps of infiltrated metal when uncovered will eventually fracture the thin ligaments of metal which froze along the leakage path. And free the casting of them.
A very pleasing solution. The hazard of the dust has been eliminated entirely. The Operator works in an unencumbered workplace, in a good working environment (problematic responses like dust-extractor cabinets were avoided). The Operators took to the solution willingly and now of their own accord swap between three pneumatic tools of differing size depending on the job.