When Metrosafe tells a unit to go to Channel 8 it is usually because another officer had asked them to switch and they didn't hear them.
EMS channel 8 is used exclusively for EMS Unit to Hospital transmissions.
In very very rare occasions do the services "cross over" and use other channels.
Urban channel 8 is a simplex channel and the pl's should still be the same. To change pl's would entail changing several radios, both mobile and portables.
D