How safe and secure are seaports such as Philadelphia?

The discovery of explosive devices on two cargo planes Friday raises many questions, among them: How carefully screened is maritime cargo, and what are security protocols at U.S. ports such as Philadelphia?

Though 100 percent screening is still deemed prohibitively costly and would cause huge delays, the U.S. Customs and Border Protection agency in January began enforcing a cargo-reporting requirement that ocean carriers and importers submit details about U.S.-bound cargoes 24 hours before being loaded onto vessels in foreign seaports.

The rule aims to help identify high-risk cargo, such as hazardous materials.

In addition, ships reaching the United States are randomly boarded by the Coast Guard, which assesses ship safety, the crew, and anything suspicious. Customs and Border Protection separately inspects ships and may order containers in ports to be opened and examined.

"Short of physical screening of all containers, there is an extensive set of layered protocols in place for imported cargo," said transportation consultant Paul Bingham, of Wilbur Smith Associates.

"I'm hesitant to say it's fairly secure," Bingham said, "because the biggest risk still is that somebody manages to corrupt the supply chain overseas and get something into a container."

Maritime security regulations are stricter than they used to be.

Lt. Cmdr. Matt Fine, enforcement chief and head of vessel boarding security for the Coast Guard in the Delaware Bay, said every cargo vessel coming to the United States has been "screened based on numerous factors, including where the vessel has been, what it is carrying, who is on board as far as nationalities and geographic areas."

It's then determined whether a ship needs to be boarded at sea.

Since the September 2001 attacks, vessels with U.S.- bound cargo have been required to send ship manifests to U.S. Immigration and Customs Enforcement 24 hours before sailing. The manifest information is transmitted to a national center and analyzed, and high-risk cargo is inspected before leaving foreign ports.

The screening measure asks for details about where the cargo came from, who the shipper is, and who the manufacturer was.

Customs does not get the same 24-hour advance notice with air cargo "because too many things are shipped last minute," Bingham said. "The whole point of air shipping is time; the cargo is often time sensitive. You can't give a day's notice before something gets on an airplane."