Are skyscrapers safe?
A modern tall building is one of the safest structures a person can be in. The engineering is mostly about what happens when something goes wrong on one floor.
The short answer
Height is not the hazard. A building of 163 floors carries the same loads per square meter as one of five. What changes with height is the time it takes to leave and the distance a fire crew has to climb, and codes written since the 1970s address both. A tower built to them is designed so that a fire or a damaged column affects one part of the building and stops there.
Fire is kept in one place
The first line is compartmentation. Floors, shafts and corridors are separated by assemblies rated in hours, so a fire that starts in an apartment burns inside a box. Steel columns are sprayed or boxed with fireproofing, because bare structural steel loses strength around 550 °C.
Sprinklers do most of the work. The National Fire Protection Association reports that where sprinklers are present the chance of dying in a fire falls by half to three quarters, and wet-pipe sprinklers are more common in American high-rise buildings than in shorter ones. A crew cannot run hose up thirty flights, so every tall building has standpipes: risers with outlets on each floor, tapped two floors below the fire. The stairs are enclosed and usually pressurized, with fans holding the air in the shaft above the corridor so smoke pushes against the door instead of through it. Smoke is what kills people in high-rise fires.
Nobody empties the whole tower
Walking 102 floors of occupants down one stair would take hours and block the crews coming up. Tall buildings use phased evacuation: the fire floor and the floors immediately above and below it move first, and everyone else stays put until the fire command station calls them. Hong Kong and Dubai add refuge floors, open levels at intervals up the tower where occupants gather and wait. Hong Kong requires them above a set height, which is why the city's towers show a stripe of open grille every twenty-odd floors.
Why elevators changed
For decades the rule was blunt: in a fire, do not use the elevator. Shafts draw smoke, sprinkler water reaches the controls, and a car stopping at the fire floor opens onto it. Recall systems send every car to the lobby on an alarm and hold it for the fire service. Occupant evacuation elevators changed that. Written into the International Building Code after the World Trade Center investigation, they have smoke-protected lobbies, shaft pressurization and standby power. The Shanghai Tower and several towers since have elevators available for evacuation, which matters most for anyone who cannot use stairs.
Structure and redundancy
A tall building is designed so that losing one member does not lose the building. Load paths are doubled and connections carry force a different way when the first way fails. The codes call it structural integrity, and it entered them after the 1968 Ronan Point collapse in London, where a gas explosion in one flat took out a corner of a 22-story block, and after the 1995 Oklahoma City bombing.
The 2001 attacks produced the largest code revision of the modern era. Work by the National Institute of Standards and Technology led to wider stairwells, stricter fireproofing adhesion and a third stair in very tall buildings. One World Trade Center was built to them, with a concrete core and separated stair and elevator systems.
Earthquakes
Tall buildings often do better in an earthquake than short ones. A tower is flexible, and its long natural period sits away from the shorter periods that shake a two-story house hardest. Engineers design for ductility, with frames detailed to bend and absorb energy. Base isolation puts the structure on rubber and lead bearings so the ground can move under it, and steel plate shear walls were invented for seismic resistance.
Japan is the record to look at. Its 1981 code revision drew a sharp line between buildings that performed and buildings that did not, and the magnitude 9.0 Tohoku earthquake in 2011 brought down no post-1981 high-rise. Towers in Tokyo swayed for minutes and the frames held. Wind is the other lateral load, and usually the one that sizes a tall building; sway in a storm is designed behavior, and the dampers that limit it have a page of their own: how much skyscrapers sway, and why.
Where the real risk sits
The risk concentrates in two places. One is older stock built before sprinklers and enclosed stairs were required and never retrofitted. Many went up under codes that permitted single stairs and no suppression at all, and bringing one to current standard costs more than most owners spend voluntarily.
The other is cladding. Facade panels with polyethylene cores carry fire up the outside of a building and bypass every compartment inside it. The 2017 Grenfell Tower fire in London killed 72 people in a 24-story block that had been reclad, and similar facades burned at the Address Downtown in Dubai. Several countries have since banned the material on tall buildings, and remediation is still running.
The numbers
In the United States the NFPA counted roughly 15,700 high-rise structure fires a year across the late 2000s, with about 53 civilian deaths. Set against the millions of people who work and sleep in those buildings, that is a low rate, and below the rate for housing stock as a whole. The limit stated in the engineering literature is deliberate aircraft impact. The twelve buildings on the famous skyscrapers page span 140 years of this engineering, and the history page covers how each failure fed the next code.