We researched this through the US National Library of Medicine, and found three studies at the National Institutes of Health that prompted us to create this graphic. Please feel free to share this - if it saves even one dog from injury, it's worth it!
Please click the infographic to see a larger version.
35 seconds - thirty five! - and you have a second degree burn.
And while a wooden deck may not be a 'perfect black body' like asphalt is, (the scientific term for a surface that absorbs heat most efficiently) even wood can be too hot for the paws of a dog or cat to handle. So when our cats go walkabout in their harnesses on a hot summer day, I'm careful to set them down in shady spots, or in the grass.
When in doubt, invoke the 7 Second Rule: if the back of your hand can't take the heat, your pet's paws can't either.