When disability, need for medical treatment, or death results from the combined effects of two or more injuries, either specific, cumulative, or both, all questions of fact and law shall be separately determined with respect to each such injury, including, but not limited to, the apportionment between such injuries of liability for disability benefits, the cost of medical treatment, and any death benefit.
Source:
Section 3208.2, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=LAB§ionNum=3208.2..