B.O., Cape Cod

A. Ventilation will not help much because the kerosene is still in the wood and years of ventilation would be required to evaporate it. But all is not lost. Check the underside of the subfloor, if it is exposed in the basement. If you see kerosene stains on those subfloor boards, it means the subfloor boards are soaked, too, and if the smell pervades the basement, then you have to replace the affected subfloor.

If you don't see any kerosene on the under part of the subfloor boards, and there is not a heavy smell in the basement, you might succeed doing this: Sprinkle lots and lots of baking soda, Speedy-Dry or cat litter on the soaked subfloor boards, leave it for an hour, and sweep it up and throw it away. Repeat. If the odor begins to dissipate, you know you are taking up a lot of kerosone, and can repeat as necessary, and with luck will eliminate the source in the subfloor. If that doesn't seem to be working, then remove the boards and install a new subfloor as well as top floor. And, of course, ventilate, ventilate, ventilate.