The collapse of a boiler tower at Ulsan Thermal Power Plant was not an unforeseeable failure of an aging structure. Investigators found that workers cut load-bearing columns beyond their allowable limit during preparations for demolition, leaving the weakened sections unable to support the tower above. Local buckling began at the remaining column sections and spread into a progressive collapse.
Seven workers were killed and two were injured in the November 6, 2025 accident at the demolition site for Units 4 through 6 in Ulsan. A transport ministry accident investigation committee reproduced the failure found at a height of about 26.2 to 27.2 meters when it analyzed the structure using measurements, material tests and completion drawings.
- Accident date
- November 6, 2025
- Location
- Ulsan Thermal Power Plant demolition site
- Casualties
- Seven workers killed and two injured
- Failure zone
- Approximately 26.2 to 27.2 meters above ground
The calculations used to plan the cuts rested on faulty assumptions. Although the steel plates in the columns became thinner at higher levels, a measurement taken at one ground-level location was applied to the upper columns. That overstated their strength. The tower’s weight was also underestimated, further widening the gap between the structure represented in the calculations and the structure standing at the site.
The review also failed to account adequately for the risk of local buckling after the columns had been reduced. Investigators said it lacked sufficient safety margins for accumulated deformation in the aging structure and for damage that could occur during cutting. These omissions explain how advance weakening intended to control the direction of a later blast instead triggered collapse before the planned demolition.
Faulty data weakened every safety calculation
Responsibility extended beyond the specialists who performed the structural review and demolition work. The principal contractor relied heavily on specialist companies and did not sufficiently verify that the final construction details matched actual site conditions. Korea East-West Power, the project owner, supervised the work directly without a separate construction manager and failed to coordinate and control the participating companies systematically, according to the investigation.
The committee recommended stronger field investigations and technical standards, tighter design and construction controls for high-risk demolition, and greater responsibility for project owners. Its findings are to be sent to relevant authorities to support possible administrative action and investigations into legal violations, while the final report is due to be submitted to the transport ministry and made public.