"We sometimes get questions about what to do if you're in a roundabout when an emergency vehicle comes through. For some reason, people don't realize you do the same thing as any other intersection - clear the intersection and then pull over once you're in a safe place."
I think the skill of the driver (of the emergency vehicle) comes into play here as well. Not hitting the siren when they're right on top of a 'civilian' vehicle causing that driver to panic.
Even in a congested state, emergency vehicles usually get through roundabouts without too much delay. Drivers tend to automatically revert to the original mode of operation, i.e. priority to the vehicle entering the roundabout, even if they didn't know it.
Our designs are usually such, that there is some escape room to allow for the 'Red Sea' effect, where two rows of vehicles part to allow a fire engine/ambulance through the middle.