Were you aware that both chipboard and softwoods can contain much more formaldehyde than MDF? I seem to recall watching a video on YouTube (10 Minute Workshop?) which demonstrated that MDF isn't particularly toxic.In terms of toxicity. There are far worse things in my world.
I doubt that I'm alone in thinking that the biggest issue with MDF is the small particle size, which means that you need point of production dust extraction and adequate filtration, something the vast majority of vacuum cleaners and woodworking "chip collectors" are incapable of providing. In my work environment arguably the mechanical grinding, cutting and drilling silicate-bearing materials such as concrete mortar, blockwork and bricks is far more hazardous because of the risks associated with silicates (silicosis).
I think that one or two sparks from time to time are far more likely to indicate surface contamination picked up in handling. Was the MDF rested on the road at any point? Was the delivery vehicle bed clean? How was the MDF handled in the yard? For that matter, is your riving knife too close to the blade? I've seen minor sparking from time to time with softwoods (bullets in one instance), OSB, plywood (resin glue pockets) and chipboard (calcite inclusions and metal), particularly chipboard which is generally made with a percentage of recycled fibres and therefore can sometimes contain whole screws. Does that make them "hotdogs"? Any timber which is handled badly, e.g.dragged across a timber yard or building site, laid down on a roadway, etc can pick up inclusions which will cause sparking
