A valve installed at the fill port of an above ground storage tank to terminate product flow when the liquid level reaches a preset level.  Other methods include but are not limited to berms, liners and other secondary containment should a leak or spill occur and overfill alarms.  Overfill alarms use probes installed in the tank to activate an alarm when the tank is either (approximately) 90 percent full or within 1 minute of being overfilled.