The buffers are not intended to stop a free falling elevator cab. The buffers are there in case the elevator control system malfunctions and the car travels at contract speed (normal speed)  past the terminal floor (top floor or bottom floor). The safeties are on all cabled elevators to prevent the free falling of the cab. Every modern elevator also has both a normal backup system to prevent the elevator from traveling past the terminal floors along with an emergency system as a sort of backup of the backup. Also, the newest elevator machines have two independent braking systems to hold the car at a given floor. Elevators are very safe.