Overfill alarms use probes installed in the tank (see illustration below) to activate an alarm when the tank is either 90 percent full or within one minute of being overfilled. Either way, the alarm should provide enough time for the delivery person to close the truck's shutoff valve before an overfill happens. Alarms must be located where the delivery person can see or hear them easily. (Overfill alarms are often a part of automatic tank gauging systems.)
Overfill alarms work only if they alert the delivery person at the right time and the delivery person responds quickly. Remember to put the alarm on an electrical circuit that is active all the time so that the alarm will always work. Many deliveries are made at night when the facility is closed. You don't want to turn off your alarm when you turn off the office lights.
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