In multi-story multifamily structures there is a lot more to consider than in single family structures. The population density increases significantly, the size of the structure increases and in high rise operations you have to be concerned with the rapid spread of heat, smoke, toxic gases and fire upward through the structure. The fact that the structural design is significantly different as the size if focused on going vertical verses horizontal.
These structures have a high life hazard at regardless the time of day. This proposes unique problems as occupant evacuation often hampers fire department suppression operations. With this fact being in place it also changes the focus of operations due to the potential need for evacuation or rescue efforts. Many of these building were constructed with fire escapes on the exterior of the building. These are often in disrepair and become involved in fire as the fire has vented out of a window and prevents the use of the exterior fire escape. Many structures have limited internal stairwells. Often these internal stairwells are not secure from the effects of smoke and heat. These prevent for safe evacuation. It is important to also consider the age of the tenants. The elder population that could live in these structures creates a special need for assistance in evacuation or rescue as they are not able to ambulate efficiently enough to travel the potential distances required for evacuating.
These structures require massive amounts of man power to be able to operate. It is recommended that for every position assigned a total of three (3) personnel be committed, one in operations, one in staging and one on deck ready for relief. This alone can make a significant impact on available resources.
Construction features can create a series of fire-control tactical concerns with the stacking of apartments that creates chases that run the entire height of the building. This design feature creates an easy pathway for fire to extend and do so without showing significant signs of fire growth and spread until large quantities of fire exist. This type of feature provides for fast moving fire extension and can compound the loss of life potential.
Larger buildings have design features that bring light and natural ventilation to rooms in the middle of the structure. These light and air shafts pose danger of allowing the fire to extend horizontally across the shaft. This feature allows the fire to sometimes by pass a fire wall or fire stop. This design will also allow fire to extend vertically as the exposures are increased and the ability to extend both via convection and direct flame contact due to lapping out of windows. The design of these windows being directing opposite or directly above each other contributes to the fire extension. One advantage is that there is not roof over these sections which eliminates the mushrooming concept and will slow the spread of fire to the upper floors.