OSHA provides timber-shoring charts for which types of timber?

OSHA provides timber-shoring charts specifically for fir and oak because these types of timber possess the necessary strength and durability to support excavations safely. Fir and oak have been historically favored in construction and shoring applications due to their structural properties, which include high bending strength and good resistance to deformation under load. These characteristics make them suitable for creating effective and reliable shoring systems that can prevent cave-ins during excavation work. The use of these specific types of timber ensures compliance with safety regulations and best practices in excavation safety, helping to protect workers from potential hazards associated with unsupported trench walls.