I'll try posting this again. The first attempt was wiped out for some unknown reason.

A 5 PSI overpressure is strong enough to destroy a high percentage of buildings and especially houses. That's enough to kill a lot of the occupants and injure many more. Even buildings not destroyed will suffer damage unless they're hardened like military bunkers.

The good thing is that this wouldn't be exactly unexpected like a nuclear attack or sudden natural disaster like what happened in Indonesia this morning. With such long leadtime, there is plenty of time to evacuate any projected impact area.

Average population density for a country is a pretty meaningless number. If you drive across much of the American west, you can find huge areas where hardly anyone lives. On the other hand, a high percentage of all Americans live within 20-30 miles of the coasts. The same is true in many other countries - you have areas of high population density and other areas where few people live.

To me, the most dangerous situation would probably be an ocean impact, and also the most likely. The tsunami-like waves generated by such an impact can travel long distances and do tremendous damage to the coastal areas where population density is often the highest. Like I mentioned before, there would be time to evacuate these coastal areas well before a projected impact if diversion attempts proved unsuccessful, but there would be tremendous economic impact. There always be a lot of people too remote to get the word, or too dense to evacuate.

We need to take the size estimates with a grain of salt. They're based on a lot of assumptions. Until we get some better measurements, preferably radar space object identification (SOI) type data, all we can do is guess.