Mahopac Falls Volunteer Fire Department members and two Putnam County Deputy Sheriffs went out in the bitter cold weather, using the frozen Lake Mahopac for an annual Ice Diving drill this week.  Fire officials say it's a physically, logistically, and mentally challenging task that can be extremely dangerous.  Firefighters and Deputies went over equipment, correct signals to communicate with the divers,  and how to correctly set up the pulley system.  Once the divers completed their dives, EMS crews monitored their vital signs.