The building was completed in late 1989, and the Sampoong Department Store opened to the public on July 7, 1990, attracting an estimated 40,000 people per day during the building's five years in service. The store consisted of a north wing and south wing, connected by an atrium.
Later on, a fifth floor was added to the four-floor building, which was first planned to be a skating rink; the skating rink was added due to regulations that stopped the whole building from being used as a department store. Lee changed the original plan for the fifth floor to include eight restaurants. When a construction company tasked to complete the extension advised that the structure would not support another floor, they were fired, before another company finished the job. The restaurant floor also had a heated concrete base with hot water pipes going through it, as patrons sit on the ground of traditional Korean restaurants, which added a large extra load as a result of increasing the thickness of the concrete slab. In addition, the building's air conditioning unit was now installed on the roof, creating a load of four times the design limit.
Collapse
In April, 1995, cracks began to appear in the ceiling of the south wing's fifth floor. During this period, the only response carried out by Lee and his management involved moving merchandise and stores from the top floor to the basement. The store management failed to shut the building down or issue formal evacuation orders, as the number of customers in the building was unusually high, and the store was not intending to lose potential revenue for that day. However, the executives themselves had left the premises as a precaution.
On the morning of June 29, the number of cracks in the area increased dramatically, prompting managers to close the top floor and shut the air conditioning off. Civil engineering experts were also invited to inspect the structure, with a cursory check revealing that the building was at risk of collapse; The National Geographic documentary series Seconds From Disaster indicates that the facility's manager was examining the slab in one of the restaurants on the fifth floor, eight hours before the collapse, when, unknowingly, vibrations from air conditioning were radiating through the cracks in the concrete columns and the floor opened up.
Five hours before the collapse, the first of several loud bangs were emitted from the top floors, as the vibrations in the air conditioning caused the cracks in the slabs to widen further. Amid customer reports of the vibrations, the air conditioning was turned off, but the cracks in the floors had already widened to 10cm.

At about 5:00 p.m. Korea Standard Time (UTC+9:00), the fourth floor ceiling began to sink, resulting in store workers blocking customer access to the fourth floor. According to Seconds From Disaster, the store was packed with shoppers 52 minutes before the collapse, but the owner did not close the store or carry out repairs at the time. When the building started to produce cracking sounds at about 5:50 p.m., workers began to sound alarm bells and evacuate customers.
Around 6:05 p.m., the roof gave way, and the air conditioning unit crashed through into the already-overloaded fifth floor (Seconds From Disaster indicates that the fifth floor slab and roof were the first to collapse, causing the air conditioning units to fall through the structure). The main columns, weakened to allow the insertion of the escalators, collapsed in turn, and the building's south wing pancaked into the basement. Within 20 seconds, all of the building's columns gave way, trapping more than 1,500 people and killing 500.