A creature has evolved to protect the herd. Its blood contains chemicals that act like pepper spray, burning the eyes and throat of anything around it. However it wants to be able to get a decent coverage on a pack of predators.
So how large an area could the blood be sprayed into?
To clarify I'm picturing a weaker member of the herd being caught - perhaps a younger one - and when the predator's bite severs an artery the blood is released.
I suppose, really, the question can be interpreted as "How high a blood pressure is possible?"
Another few points:
- Gravity: Similar to ours
- Animals, same basic structure - hearts pumping blood around and such.