Believe it or not in my research it’s a little obscure to get an accurate answer! So I’ll mention human comparison as we are usually more sensitive to surface temperatures than a dog! I’ve seen where it has been said temperatures of 110° can burn a human.  I’ve also read  surface temperatures of pavement  120° and above can burn a human’s and dog’s  feet in less than a minute…When a dog’s pads are properly developed and conditioned they are stronger than a humans skin but I always will error on the side of caution and still stick to the human specs! But the issue becomes 2 fold with dogs because of their pad structure where they emit their heat from so even warm pavement can inhibit their cooling process! So if it’s too hot for the dog, it could burn their pads and even if it’s too warm, it can inhibit their cooling process! That’s why we spray the dog’s pads constantly throughout our adventures in warmer weather as well as get them cool downs in waterways when possible! And also keep in mind from surface to surface the temperature can have a large disparity as concrete is usually lighter in color and will reflect the sun so temperature stays cooler,  where as dark surfaces like asphalt absorb the sun so they will be hotter! I did a comparison video above!  So my rule of thumb is when temperatures of surfaces on my thermometer are above 90° I will start to consider if we need to get off the trail and end our adventure and other options how we can safely  proceed! I will avoid surface  temperatures greater than 95°. Additionally, I will avoid stopping on warmer surface temperatures, most importantly when possible, because like a human, if the dog is just standing there without lifting their paws as they do when they’re moving, it can exacerbate their heat exposure, even more! Of course I always carry dog booties in the unforeseen instance that we run into hotter temperatures. I can use the booties on short distances to get us past a situation that may be what I consider too hot! But booties can present another problem as I mentioned the dogs emit their heat from their pads, so the booty can trap their heat  in and again, really inhibit their cooling process, which could create a whole other problem! There’s also some waxes that are made for dogs pads like Musher’s Secret, which can be an option for limited heat protection in certain scenarios! Keep in mind also my practices work for me and my breeds of dogs, but can vary from breed to breed and even from dog to dog!