What was the most important pre-World War II high-rise feature regarding fire spread?

The key feature regarding fire spread in high-rise buildings before World War II is the absence of a central air conditioning system. This is significant because a central air conditioning system can act as a conduit for smoke and heat, allowing fire to spread rapidly through the building via the ductwork. Without this system, high-rises depended more on natural ventilation, which limited the potential for rapid fire spread because smoke and heat would not have a dedicated path to travel through the building.

Other features, such as fire escapes, non-combustible materials, and multiple exits, indeed play essential roles in fire safety; however, they do not directly prevent the spread of fire in the same manner that the absence of central air conditioning does. Fire escapes provide a means of evacuation, non-combustible materials help inhibit fire from spreading, and multiple exits improve accessibility, but none of these features addresses the internal mechanisms that can facilitate fire spread as effectively as the presence or absence of a central air conditioning system.