According to Cal/OSHA, every employee in an excavation must be protected from cave-ins by an adequate protective system, unless which of the following conditions is met?

• The excavation is sloped at a 1:1 ratio and is less than 8 feet deep.
• The excavation is less than 4 feet deep and a Competent Person has examined the ground.
• The excavation is made entirely in stable rock.
• The excavation is less than 6 feet deep and no workers will be in the trench for more than 15 minutes.