During an emergency, what is the primary role of a life vest?

The primary role of a life vest is to ensure buoyancy in water. Life vests are designed specifically to keep a person afloat, which is critical during an emergency situation where there is a risk of drowning. They are constructed with materials that provide buoyant support, allowing individuals to remain on the surface of the water without expending energy, which is essential for survival until rescue.

While warmth and protection from environmental factors can be beneficial in certain situations, the fundamental purpose of a life vest is to provide flotation support. It is not intended to protect against electrical shock or to reduce body weight, as these aspects are unrelated to the vest's design and primary function. Thus, ensuring buoyancy in water is the essential characteristic that makes a life vest a vital piece of safety equipment in emergencies involving water.