What is the characteristic feature of the two-person extremity carry?

The characteristic feature of the two-person extremity carry is its ability to be performed in tight spaces. This technique is particularly useful in situations where maneuverability is limited, such as in narrow hallways or small rooms. Firefighters can effectively carry a victim or load by using both individuals positioned at the extremities—one person at the head and one at the feet—allowing for a compact formation that can navigate confined areas efficiently.

The necessity of a chair or backing board, as noted in the other options, is not a requirement for this specific carry method. While a backing board can provide additional support for an injured person during transport, it is not integral to the two-person extremity carry itself, which primarily focuses on utilizing personnel strength and coordination in restricted environments.