The document discusses principles of patient assessment for EMS providers, focusing on properly sizing up the scene. It outlines the key components of scene size-up, including identifying hazards, establishing body substance isolation, determining the mechanism of injury or nature of illness, and assessing the number of patients and additional resources needed. The document provides examples of common hazards at a scene, guidelines for use of personal protective equipment, and how understanding laws of motion can help anticipate injury patterns based on the mechanism of injury. It emphasizes the importance of thoroughly sizing up every scene to ensure safety and guide patient care.