The HSE regs say that in a commercial environment any task must be undertaken on the most suitable equipment - which most of us take to mean the one with the least risk of injury or accident. Technically it is possible to make a dado head safe, I suppose, but when there are many safer/faster/better/more convenient ways to do this, why bother? In reality the HSE rarely compell - until you have an accident, in which case you find yourself being accused, or worse prosecuted, for "failing in the duty of care"...
If you'd like a personal reason for not using them, its simply that they are almost impossible to guard properly (i.e. very few machines have proper guarding available - my saw does, but that's another matter) and if you've ever used one and hit a knot (with the ensuing kickback, near finger event and bad language
) you'll know why I for one wouldn't have one one a table saw. Funnily enough, I have less qualms about using them on a crosscut saw (by that I mean a radial arm or pull-over type), as any kickback will direct the workpiece away from me and towards the fence and that's where most of the dado or trenching heads I've seen in commercial shops were installed, although there is/was always the hassle of having to locknut the dado head to prevent it coming off under braking! For an apocryphal story about dado heads (from the Land of the Free - and a pro site to boot), look here
http://www.woodweb.com/knowledge_base/Eyewitness_Injury.html - look for the piece from Contributor K :shock:
Surely it boils down to this: whatever people want to do in the privacy of their own shops is their own business (mostly) - when they start to publicly encourage others to follow suit and take risks, that's a different matter. The comment about measure twice, etc. on my posts refers in part to the fact that,
despite being a trained wood machinist I have still damaged both my thumbs in work-related accidents, and in one case required reconstructive surgery - and (in theory) I knew what I was doing.....
Sorry for the long post.
Scrit