Others result in really annoying tiny chunks of fiberglass on your fingers for a few days.
At a practical clinical conference I went to recently, one of the workshops offered an hour of putting on learning about various fractures and practical casting and fracture re-setting tips, followed by an hour of putting casts on each others' arms.
We learned some neat practical tips to make slightly casts, from how to cut the material so it doesn't bunch up between the thumb and pointer finger, to how to apply a bit of extra padding where the cast is likely to have a few extra pressure points.
For example, we learned "a good cast is an ugly cast" - if the cast is made properly, and is applying enough immobilization at the right area of the bone, there will be knobs and finger indententations from where the person applying the cast moulded it correctly (I don't think that the teacher was referring to a "really" ugly cast, like the one in the picture, that my friend Jordanna moulded... unlike me, though, at least she remembered Step #1...see below).

Or, we learned that any forearm cast - even for a single broken tiny bone in the wrist - should go up to within two fingerbreadths of the antecubital fossa (elbow crease). That way, if you fall on the cast, you don't end up with a radial/ulnar double bone fracture halfway up the arm where the cast ends (which could end you up in surgery) - instead the elbow joint can take the brunt of the force.
When it came time to apply the casts, though, I unfortunately forgot step #1.... put on gloves. I've had some experience applying plaster casts, where you can easily wash your hands afterwards with no residual... uh, residue.
However, for fiberglass casts, if you don't wear gloves, your fingertips get coated in tiny chunks of fiberglass cast material. Try as you might to wash it off, it's there for good for the next few days to wreak havoc on your sensory nerve endings and make your hands feel like they're desperately in need of moisturizer.
Fortunately this mistake didn't kill anybody. All the same, it's still one that I'll chose to not make again.



