The hairpin I know is basically a three step curved sharply to the left, half a turn. The footwork is the same as the three step. Using the Guy Howard/IDTA version that starts with the man's LF, that is heel, heel-toe, toe-heel.
Note the first step is not heel-toe as that would imply a rise and require the next step to be toe or toe-heel. That's not to say that the LF doesn't roll through from heel to toe as the next step is taken just as it would if walking normally, but there is no deliberate movement onto the toe.
I can't see a foxtrot hairpin in "popular variations" (oh for an alphabetical index!) but it does show natural hairpins in quickstep which would be tightly curved feathers.
Rgds
Howard