I entered the Philadelphia, PA Fire Academy in Oct. 1969 and was trained in the use of the life net. We used to catch each other in the net for practice. There were injuries. Some cadets were hurt quite seriously. We were told that use of the life net was only for desperate situations. In thirty six years with the Dept. I never used a life net or heard of anybody using one. As a matter of fact, they were removed from service sometime in the 1970s as they were deemed unpractical and dangerous.
ETA: Link to column: Did firemen once use nets to rescue people from burning buildings? - The Straight Dope