If the nail is black, you will lose it. The best drill is to make a hole in the fingernail immediately after the injury. This is best done by heating a needle and touching it to the nail until blood comes out. Sounds yucky and painful but it is actually painless. There are no pain sensors in the nail and you stop when you hit blood, which is under pressure and immediately comes out. The drill is NO HEAT for 24-48 hours, then warmth. Heat causes swelling, which is the last thing you want to do. So alternating hot and cold is the wrong train in the wrong direction. If you can wrap with a circumferential pressure bandage before swelling takes place.
Thank you for your input!
An internet post elsewhere says to drill a hole, but this one method, but is not necessary. When you smash a fingernail blood immediately begins to accumulate under the nail, separating it from tissue. This blood must be drained before it coagulates. The "hot needle" trick is absolutely positively painless. If done soon after the blow you won't lose the nail.