I wasn't able to find specific regulations for using a three-step ladder to install twelve-foot drywall sheets. However, here is some general safety guidance based on industry standards and best practices:

• Ladder Load Capacity: Ensure the ladder can support at least four times the maximum intended load, including the weight of the user, materials, and tools.

• Ladder Angle: When using a non-self-supporting ladder, position it at a 75½ degree angle from the horizontal.

• Ladder Spacing: Ensure that rungs, cleats, and steps of portable ladders are spaced not less than 10 inches (25 cm) apart, nor more than 14 inches (36 cm) apart, as measured between center lines of the rungs, cleats, and steps.

• Ladder Safety Systems: Each ladder safety system allows the employee to climb up and down using both hands and does not require that the employee continuously hold, push, or pull any part of the system while climbing.

• Fall Protection: When working on a scaffold more than 10 feet (3.1 m) above a lower level, ensure each employee is protected from falling to that lower level.

• Ladder Inspections: Ladders are inspected before initial use in each work shift, and more frequently as necessary, to identify any visible defects that could cause employee injury.

• Ladder Usage: Each employee faces the ladder when climbing up or down it and uses at least one hand to grasp the ladder when climbing up and down it.