ANTIOCH (CBS SF) — Crews contained and cleaned up a small amount of spilled radioactive material Thursday that forced the evacuation of several apartments next to a construction site, according to Contra Costa County fire officials.

At about 9 a.m. crews responded to a report that a piece of equipment used by surveyors was run over by a construction vehicle and spilled out a very small amount of radioactive material, Contra Costa County Fire Protection District Fire Marshal Robert Marshall said.

“There is zero contamination on the site at this point” and no one was injured or exposed to the material, Marshall said.

The material, cesium and americium, are common in medical and industrial uses and are found in certain types of smoke alarms.

As a precaution, however, about 50 units in roughly eight nearby apartment buildings were evacuated. Residents were allowed back into their homes at about noon, Marshall said.

In addition to the fire crews, the county’s hazardous materials team responded, as did teams from PG&E and the county’s water district.

The construction site is on Tabora Drive, near the intersection of James Donlon and Contra Loma boulevards, which were closed to traffic while the cleanup continued.