Plainly visible from West Seattle, thousands of shipping containers come and go daily from Terminal 18 on Harbor Island, where they are scanned with gamma rays, scoped with radiation detectors and analyzed by computer.

The security system at Terminal 18 is designed to limit access and keep track of the movements of all containers, trucks and people throughout the facility, said Andrew McLauchlan, senior vice president of SSA Marine, a Seattle-based private company that runs the terminal.

About 250 ships call at Terminal 18 each year to load and unload approximately 800,000 "twenty equivalent units" of containers. The TEU is the standard measurement used by the shipping industry meaning a 20-foot-long container. Most containers are 40 feet long and are owned by the shipping lines or leased.

There's been much worry nationally over the fact that relatively few shipping containers are opened and inspected by federal agents. They are not all opened and inspected at Terminal 18 either. However, every container coming into that terminal is electronically scanned for cargo that doesn't match what's listed on the ship's bill of lading. Agents look for weapons, narcotics, copyright and trademark violations and other problems, he said.

Containers that raise suspicion are lined up end-to-end for a sweep with gamma rays.

In some cases, an electronic seal is attached to a container when it is loaded with merchandise at the factory. The container's contents are coded into the seal along with the route the container is to take, said Mick Schultz, spokesman for the Port of Seattle.

Cargo in some containers is investigated and cleared before the container even arrives in the America.

The United States has agreements with 42 seaports around the world, where all containers headed for the states are screened 24 hours before the ship leaves port, said Mike Milne, spokesman for U.S. Customs and Border Protection. In many cases, agents in the United States continue to analyze the cargo for danger while the ship is at the sea.

U.S. Customs and Border Protection also works with manufacturers and the companies in their supply chains, said Tom Hardy, Seattle field director of the federal agency.

When trucks arrive at the 196-acre Terminal 18, they line up to go through guard stations where drivers' identification cards are checked.

A radio-frequency identification tag is on every container. Radio-frequency sensors mounted on the terminal's towering light poles continually track the movements of each container, truck and driver, McLauchlan said.

The high light poles also support 35 cameras, some of which are moveable, which scan the waterfront as well as the dock.

There are also monitors on all of the terminal's "top picks," the large forklifts used to move containers around the dock.

Truck drivers are checked again for ID.

When longshoremen arrive for work, they show an identification card to a television monitor, which relays the image of the ID to a nearby guard station.

There are also roving security guards, including a K-9 unit, keeping watch all day and night at Terminal 18.

At another site on the terminal, trucks slowly pull their loads between two rows of jersey barriers where they pass through two sets of radiation monitors. Trucks can be moving up to 20 mph as the monitors look for nuclear or radiological materials. Every container that arrives at Terminal 18 goes through the radiation monitors, whether the container is full or empty.

Occasionally nuclear medical equipment and even marble, with its natural radioactivity, can trigger the monitors.

Any containers that seem dubious are pulled aside and scanned with a hand-held radio-isotope identifier, which can find radioactive materials and reveal where they are located within the container.

A half-dozen suspicious containers are lined up end to end. A truck with a long hydraulic arm reaches over the top of the containers for a look at their other side with a gamma-ray scanner.

A computer image of the container's contents shows inspectors anomalies in the image. They know what a container full of tennis shoes is supposed to look like. So if there are other items among the shoes, the gamma rays can reveal them. The image is stored on computer for future reference.

Besides all of the security scans and inspections, routine customs inspections are still conducted as well to make sure import regulations are followed and duties paid, Hardy added.

Container operations at Terminal 18 are managed by SSA Marine, which also manages shipping operations at Terminals 25, 30 and the Bell Street Terminal. The company also has port operations in Tacoma, Portland, Oakland, San Diego, Houston, Jacksonville, Charleston and other locations, including Mexico and Panama.

SSA Marine shares security detail at Terminal 18 with U.S. Customs and Border Protection and the U.S. Coast Guard.

Tim St. Clair can be contacted at tstclair@robinsonnews.com or 932-0300.