Short answers, pulled from the story.
Fireproofing is the process of rendering structures, materials, or objects resistant to fire, classified as a passive fire protection measure. It works by applying materials or systems that delay heat transfer, maintain structural integrity, or prevent combustion; common methods include spray-applied coatings, concrete encasement, gypsum board cladding, and liquid convection cooling in hollow structural members.
Structural steel reaches a critical temperature of approximately 540 degrees Celsius, at which point it begins to lose the strength needed to support a building's frame. Fireproofing methods such as concrete encasement, gypsum plaster wrapping, and spray-applied fire-resistive materials are designed to delay the steel from reaching that threshold.
Paper documents are destroyed when internal vault temperatures exceed 176.7 degrees Celsius. Fireproof vaults made of concrete or masonry combat this by releasing chemically-bound water as steam into the vault chamber when exposed to fire, keeping temperatures below that threshold.
Magnetic media such as data tapes lose data above 51.7 degrees Celsius, the Class 125 threshold, and microfilm is destroyed at 65.5 degrees Celsius, classified as Class 150. Vaults engineered to the more stringent Class 125 standard are called data-rated vaults.
Asbestos was used for fireproofing because of its natural heat resistance; it was applied as spray, pressed into sheets, mixed with cement binders, and added to fabrics and building materials. It was replaced after it was proven to cause cancer, which prompted a large removal-and-replacement industry and a shift to endothermic materials such as gypsum and cementitious products.
An intense fire in the Channel Tunnel, which connects the United Kingdom and France, reduced the concrete lining of the undersea tunnel to about 50 millimetres. The event demonstrated that unprotected concrete cannot withstand severe hydrocarbon fires and contributed to the development of building codes through the European Eureka Fire Tunnel Research Project.