By mid-October, containers leaving the Port of Charleston, SC, will face an additional security step on their way out the door.

The port has installed seven new radiation portal monitors to check outbound containers for dirty bombs or possible nuclear weapons. The containers will be in use by the week of Oct. 17.

The Associated Press reported that the monitors – which are big enough to drive a truck through – will scan every container moving out of the terminals and the results will be sent electronically to a remote lab for analysis. If anything suspicious is found, the load will be pulled aside for further check.

Some critics wondered why the containers aren’t scanned as they come off the ships, rather than as they are on the trucks leaving the port.

Pam Zaresk, ports director for U.S. Customs in Charleston, told The AP that it isn’t logistically possible to scan the containers as they come off the ships because there are as many as 12 ships being unloaded at any given time.

Similar scanners are also being installed at the Ports of Long Beach and Los Angeles in California. Scanners at those ports are expected to be in use by the end of the year.

The scanners are already in use in several ports throughout the country, including Jersey City, NJ, and Oakland, CA.

Oakland installed 25 of the devices in April and became the first port to begin scanning all of its incoming containers.