I tried to replicate this experiment.
I tuned to the local AM station so that there would be some audio for the FCI TDA2822 to amplify.? The rig has an internal 4 ohm speaker.? I turned the radio up all the way.? It was very annoying.
With my calibrated finger firmly on the TDA, it would slowly get warm.? I did not keep my finger on to the point of discomfort.? After around 30 seconds I would take my finger off for 10 seconds.? When I returned my finger to the TDA, it was not warm to the touch.? This was repeated a few times.
For this instance, there was no failure or thermal runaway of the FCI TDA2822 powering a 4 ohm speaker at full volume.
Arvo W0VRA