Los Angeles ( CNN ) -- City workers in Southern California discovered a backpack Monday filled with grenades and other explosive devices , a sheriff 's spokesman said . The municipal employees came across the backpack in a storm drain in Placentia around 9 a.m. , Orange County Sheriff 's Department spokesman Jim Amormino told CNN . Police and bomb squad personnel subsequently responded and located six grenades , blasting caps , fuse igniters and some white and black powder , according to Amormino . These were discovered in the backpack as well as buried in dirt nearby . It appears the explosive devices were put in the area intentionally , according to the sheriff 's department spokesman , who added that he believes they had been there for some time . FBI agents were on scene Monday afternoon helping sheriff 's department members in their investigation , as is routine when explosive or suspicious items are found , said Ari Dekofsky , a spokeswoman for the bureau 's Los Angeles office . There was no immediate threat to the public 's safety , added Dekofsky . By 2:45 p.m. , all the explosive devices had been safely detonated , said Amormino . Placentia is a city of about 50,000 people located just north of Anaheim and 30 miles southeast of Los Angeles .
Emergency workers in Placentia found the backpack in a storm drain , a sheriff 's spokesman says . The explosives , blasting caps and two igniters were in the backpack and nearby dirt . The explosive devices likely had been there for some time , sheriff 's spokesman says . They have been safely detonated , he says .