You are looking at the floor of the master bedroom. The first weekend after we bought the house, we went through with one of those home lead-paint test kits. Know what we found? Lead paint---lots of it---all over the house.
It turns out that the person who owned the house before us was a painter, and, well, it seems that he painted the house with whatever he had sitting around. So we have lead paint over all of our floors. It's on the walls too---not just the trim.
Our first plan was to sand it, but that was quickly dismissed after we learned about lead paint. So we went to the paint store and got this stuff called Peel Away. The stuff is a very caustic paste which you smear onto the wood, cover with paper, and let sit for a few hours. The paper, paint and paste just peels off.
The one problem with the peel away is that it leaves a residue which is kind of nasty. We have a solution which you are supposed to treat with. But our main goal would be to sand after peel away.
Anyway, turns out that after I learned about Peel way, we discovered that some of the people with sanders in town have HEPA (high efficiency particle aerosol) filters, whhich might be able to safely pick up the lead paint anyway. They also have special sanders for getting under the radiators. We're not sure what we are going to do now.