How long can beef be left out to thaw before it's not safe to eat?

officially, there is a 4 hour "window" of safety in that your meat can be between the temps of 40 degrees and 140 degrees for 4 hours after that time, it should be either reheated or chilled. Now, if you are thawing a chunk of frozen meat, obviously your meat temp will be much lower thatn 40 degrees. however, where the danger lies in that while the meat may still be pretty cold and even frozen on the inside, the outer edges all will be much warmer and could be a problem. That is why it is recommended that you thaw all meats in the fridge. A couple of hours on the counter won't hurt it or you. And if it does go past that window of safety, make sure you are cooking it to at least 160 degrees or well done.