Heroes of the Flames
Heroes of the Flames is a 1931 American Universal movie serial. Although once considered to be lost, it has survived and a print has been preserved by Universal as of 2016. It stars Tim McCoy (in a break from his usual cowboy roles) as a firefighter who is developing a new kind of flame retardant, but his work is constantly being disrupted by a rival named Don Mitchell (Gayne Whitman) who wants the formula for himself as well as the leading lady, played by Marion Shockley. Fittingly, seven of the 11 cliffhangers involve burning buildings with  at least one principal trapped inside. It is unusual for the manner in which chapter recaps are handled: A reporter at a local newspaper repeats a summary of the previous episode as he takes it down from a witness on the phone. It also has no music at all—the opening titles are accompanied only by sound effects (sirens, bells ringing, fire crackling, etc.). It's also the only film in which future star Bruce Cabot appeared in an uncredited bit part.