Ridgway Spark Arrestors? Not familiar with that term. Do you mean beartrap basically errr?
I would think they took them off because of the way they were steaming. It was too much. Any steam locomotive runs well without any sort of spark arrestor. Only problem is, is that you start fires all time. If it's a coal or wood burner.
But I would think that most cinders actually would totally burn out by the time they hit the ground if you don't have a spark arrestor on the engine, because they'd shoot higher in the air and come down slow. But then again they land farther away from the road bed and make it harder for the water car to put out. Another problem would be that you'd get alot more draft through the fire and probably pull alot larger cinders out and through the tubes and out the stack, those would probably be red hot when they hit the ground.
They certainly look better without spark arrestors. Especially the mudhens!