Cal. LAB § 7603

The maximum weight of materials stored on building floors or load-carrying platforms, except those built directly on the ground, shall not exceed their safe carrying capacity. Material, when stored, shall be piled, stacked, or racked in a manner designed to prevent it from tipping, falling, collapsing, rolling or spreading. Racks, bins, planks, sleepers, bars, strips, blocks, sheets, shall be used when necessary to make the piles stable.