Blood threshold <-- best description for it.

Hmmm, how to word the way I'd handle it.
Make it use the scale depending on what's happening.
If it's based on the number of frames for the scaling then you could simply multiply to get different amounts of silly.

So we make a scale of 0-10 (0 = disables blood, yay for everyone who's asked for that)
So for the sake of this the scale = X

Weak impact: none

Heavy impact: INT(X*0.5) frames of bleeding.
It'll round up to an integer so you'd bleed for 1-5 frames depending on the setting.

Fracture: X*2 frames of bleeding.
More blood, but still not too silly. 20 frames at the highest.

Dismemberment: X*20 frames of bleeding before it stops.
Top setting that'll give 200 frames of spraying, lowest it'd gush out a bit then stop.

You could also scale the blood particle sizes with the scale, where a low number would produce small mist looking ones (think along the lines of the blood on Equilibrium), and a high one would have the current stupid drip looking ones.

Also since multiplying anything by 0 = 0 setting the scale to 0 would disable blood.

OFC the numbers would need tweaking if it was done that way, but it shows that it's not only a simple to do & feasible suggestion, it could also have the added effect of giving the no blood option lots of people ask for.