When building a high rise (defined as being 75 feet or greater in height measured from the lowest level of fire department vehicle access to the floor of the highest occupiable story), it is especially important to consider smoke control. Due to their size, high rises are much harder to evacuate, and people may be stuck inside longer, inhaling smoke, if there is a fire. While many of the forces driving smoke movement inside of buildings are common to low, high and mid rises, there are several things to consider that are unique to high rises.
- Stack Effect is the vertical movement of air within a building. It is a result of differences in air density between either the building’s interior and exterior or two interior spaces. While this is a factor for all buildings, it is particularly important when discussing high rises, because that is how fire moves between floors.
- Piston Effect is related to the pressure differentials caused by the movement of an elevator car. High rises experience this more strongly due to the number of elevators and the speed at which they must travel.
- Wind affects pressure differentials as well, especially if a window happens to be broken during a fire. It may be worthwhile to do wind tunnel testing or computer modeling when designing the smoke control system for a high rise.
- Stairs in high-rise buildings are not designed for a total building evacuation, meaning that if an evacuation is necessary, people may find themselves waiting in the stairwells with the doors propped open. This makes tenability important, and fan size must be considered as well to take into account these factors.
- Refuge Areas are necessary due to the large number of stairs people will have to walk down to get out of the building- some people will have to take breaks between floors. Therefore, it is important to create areas similar to the stairs, with tenability and pressurization, for people to rest in.