SAYING A BRACHA IN A CLEAN PLACE
It is written in Devarim that when a person is saying "a holy thing, the place should be clean." For that reason, we show respect to Hashem, by saying brochos in a place that is clean. When the Rabbis say "clean", they mean that he is four amos or eight feet away from anything dirty that smells. If there are dirty diapers or garbage that is covered and cannot be smelled, then Tefilos may be said.