If your injured by a falling object at work (at a job or construction site, or any where you are working), then you will have claim for California workers' compensation, and possibly a third party if the falling object was due to the negligence of a third party not connected with your employer.

The truth is construction workers generally don’t work in a vacuum, and they use painting machinery, cranes, and cleaning equipment while up on scaffolds.  Things can fall and cause severe head wounds.  Also, construction work may be going on simultaneously on different parts of the site. If a person above you drops a bucket of tools or accidentally spills paint, you could lose your balance and fall off the scaffold; thereby causing injury.  

A good California construction lawyer will review the facts of your "object falling on you injury" to see if there is also a third party to pursue for legal damages in addition to any California work comp remedies.