A second dry ice bomb exploded at a Los Angeles airport Monday night and two more were found, just a one day after an initial dry ice explosion on Sunday.

Four dry ice bombs have been located at LAX so far, all placed in areas restricted to employee access, the Los Angeles Times reports.

No injuries were reported in either explosion, and the dry ice bombs had little impact on airport activity. But detectives from the local police and the FBI are investigating how the devices got placed in secure areas, including outside the terminal near the planes themselves. Authorities said they do not suspect terrorism at this time.

The bombs are very simple, just dry ice in a bottle.

[Los Angeles Times]