The metallic grinding dust from most steel and cast iron alloys do not present a significant health risks.
They quickly rust away to nothing. The dust from the wheel it's self is a different story. It does not
dissolve and can not be absorbed. 90% of that dust inhaled will end up as disgusting on a tissue when
you blow your nose. The other 10% is yours to keep for the rest of your life. In a home hobby setting
that may add up to only a few grams over the years. It is still something that a simple dust mask can
greatly reduce.
When you get into more exotic materials such as red brass, some copper alloys, high nickle cast and
hard steels containing higher levels of manganese, the metal dust also becomes a health hazard.
Red brass and copper may contain beryllium. That is a very nasty thing if inhaled!
The minimum safety requirement for grinding is a dust mask.
A shop vac nozzle set close to and safely secured near the grinder exhaust would be a great plus.
The ultimate would be ieezitin's suggestion a full face respirator. They can be very expensive unless
you know where to shop for one. If you have a military surplus store near you that would be a place
to look for one. If not, there are many online stores who sell exactly what is needed.
Such as
This One
They may not have been manufactured for grinder safety, and if you walk outside wearing one the
local law enforcement may have some questions for you.
Bottom line is they work perfectly for reducing the health risks of grinding.
Rick