SAN DIEGO -- A service dog signaled the possible presence of an explosive material in a cargo facility at Lindbergh Field Thursday afternoon, prompting the evacuation of the building and a search by a bomb squad.

The animal alerted its handler, a harbor police officer, to the potentially dangerous substance in a container in the stand-alone United Airlines freight facility during a routine sweep about 3:15 p.m., airport spokeswoman Diana Lucero said.

Authorities cleared workers out of the structure and notified the San Diego Fire-Rescue Department, which sent in an explosives materials team to investigate.

The personnel used an X-ray device to identify the contents of the suspect package, one of three with listed contents of testing equipment for aircraft components, SDFRD spokesman Maurice Luque said.

The scans revealed items that appeared consistent with their designation on a shipping sheet, but authorities were checking with the assigned recipient of the containers to make sure.

No flights were delayed by the incident, and public access to the airport was unaffected, Lucero said.

The process of clearing the containers could last into the early evening hours, airport information officer Steve Shultz said.