[jkohler70]

I can only advise that, while stepping on the vent may cause pain, there is virtually no chance of an actual injury. An object must be at least 111 degrees F to cause a second degree burn, but that would take hours. It would take 6 seconds for a 140 degree object to cause a second degree burn. Your furnace is likely putting out air no hotter than 100 - 125 degrees.
The vent might "hurt", but it probably won't "harm".