At just 125°F burning can occur in 60 seconds. To put it in perspective, and egg can fry in 5 minutes
Of course the above temperature correlations will fluctuate depending on variables such as humidity, direct or indirect sun, wind, etc.
Signs of Burned Paw pads include:
Refusing to walk
Licking/chewing the feet
pads that are discolored, often darker in the center than in other areas
missing part of pad
Also, just like people, when pets swim the water softens the pads of their feet making them more susceptible to burning.
Place the back of your hand on the pavement. If you cannot hold it for seven seconds, it's too hot to walk your dog on it! If you're considering putting socks on as a barrier be sure to watch your dog closely, many dogs will chew (& consequently ingest!) the socks.
What Can you do Instead:
Limit the dogs' time on hot asphalt or pavement, walk them in the grass or gravel surfaces.
Be aware that gravel can get hot too.
Walk them earlier and
Bring a towel with you on the walk so if you stop for any length of time the dog can sit or stand on the towel rather than the pavement.
Use Paw Protection such as booties or Paw Wax
In addition to painful burns, pets are also susceptible to heat stroke as well.
Our close friends dog died last summer following a playful run with the kids, when they got back from playing, he collapsed. He was gone before they even made it to the vet.