THE Grenfell Tower disaster has left many wondering why it’s still standing after it was gutted by an inferno that burned for more than 24 hours and killed at least 79 people in London.

Images of the raging fire last week ravaging the high-rise building as smoke bellowed from the windows and those trapped inside jumped to escape flames has drawn many comparisons to the 9/11 attacks on the World Trade Center in New York City in 2001.

Firefighter Leon Whitley, 34, climbed to the 15th floor of the burning Grenfell building despite fearing it could collapse like several of the World Trade Center buildings.

“I’d want someone to go in and rescue my son, so that’s what I did,” he told The Sun.

While Grenfell wasn’t subjected to the impact of a commercial jet and its fuel like the Twin Towers, it was engulfed in fire more similar to that of the old 7 World Trade Center during the 9/11 attacks.

According to the official version of events, flaming debris from the burning Twin Towers flew into the 47-floor skyscraper — sparking blazes all over the building — until it finally came crashing down after seven hours.

The National Institute of Standards and Technology concluded that the heat generated by the infernos brought the tower down — making it the first and only steel skyscraper in the world to collapse because of fire.

But with Grenfell having burned about four times longer than the WTC7 yet remaining upright it’s a comparison that has left many commentators and conspiracy theorists scratching their heads.

“London high rise fire, why didn’t that building collapse down on its foot print? Way more damage than the WTC’s. Just makes you wonder,” one Twitter user wrote.

It was a sentiment echoed by many.

“The Grenfell Tower in London was ablaze for 12 hours and it didn’t collapse. The WTC7 was on fire for (less) ... and collapsed?” another wrote.

So London building burns for dozens of hours and never collapse but WTC 7 had small fires and was completely destroyed? pic.twitter.com/wGeZZlZ9z5 — karl jr (@karlholmesjr) June 19, 2017

https://t.co/n9rCesJiAR

Why did 3World trade center buildings collapse while the intense fire of the building in London didn't? C4 self — Jim (@cabman49) June 19, 2017

my facebook feed is full of structural engineers saying that 9/11 was an inside job because the buildings in London didnt collapse amid fire — Ralph Janik (@RalphJanik) June 18, 2017

Despite the fate of the WTC7, structural engineers quickly declared the Grenfell Tower was unlikely to collapse when it was engulfed in flames. The fire continued to burn for more than 24 hours but official advice that it wasn’t in danger of collapse remained in place.

“Our specialist urban search and rescue crews and a structural engineer have checked the building and said that it is not in danger of collapsing and that it is safe for our crew to be in there,” a statement from the London Fire Brigade read at the time.

Experts from Kensington and Chelsea also predicted it was unlikely the 24-storey tower that once housed up to 600 people in 120 apartments would fall down.

One structural engineer, who didn’t want to be named, told news.com.au that Grenfell was made up of concrete slabs, beams and columns.

I'm saying that explanations for the 9/11 collapse, however wrong you think they are, are contingent on massive factors London didn't face. — Dave C (@armiesinsleevie) June 18, 2017

Building in London was built much stronger, than twin towers didn't collapse after getting burnt completely! #LondonFire — Tweet Magazine 🌎 (@ZaraMishelle) June 18, 2017

The apartment block was built in the early 1970s at a time when strict new building regulations had come into effect to ensure high rises would not fall down in the event of a blast or major fire. The regulations were introduced following a deadly gas explosion at the Ronan Point high-rise in East London. It marks the only time a block of flats in London has collapsed.

Emeritus professor of structural engineering at Newcastle University, Dr John Knapton, who advised insurers Lloyds of London in the wake of the Twin Towers terrorist attack, said:

“I don’t think this building will collapse because in 1968, a block of flats at Ronan Point in East London partly collapsed as a result of a gas explosion in a kitchen,” The Telegraph reported.

“As a result of that, the design of tower blocks in the UK changed from about 1971 onwards.” From then on, the design had to allow for an explosion or a fire to remove part of the supporting structure and for the building to remain standing.

Dr Knapton said that if “Ronan Point (had) not happened, Grenfell Tower would have collapsed by now”.

The World Trade Center was made from composite slabs — concrete poured over steel deck — as well as steel beams and steel columns with a fireproofing coat. It was built in the 1960s and was about six times taller than Grenfell Tower, according to a structural engineer.

An extensive inquiry by the National Institute of Standards and Technology into the collapse of the twin towers found the planes severed and damaged support columns and dislodged fireproofing.

Around 10,000 gallons of jet fuel were spewed over many floors starting widespread fires. Temperatures of up to 1000C caused the floors to sag and the perimeter columns to bend, causing the sounds of “explosions”.

The massive weight of the floors dropped, creating a dynamic load far in excess of what the columns were designed for. Debris was forced out of the windows as the floors above collapsed.

“The Twin Towers collapsed because the aircraft fuel ignited the contents of the building and it was the burning of the contents of the building which caused the steel columns to lose stiffness,” Dr Knapton said.

“UK buildings are much more robust, or tolerant of losing structural capacity than the Twin Towers.”

But experts claim Grenfell’s exterior cladding, which contained insulation, helped spread the flames quickly up the outside of the public housing tower early Wednesday.

Some witnesses said they had never seen a building fire advance so quickly.

megan.palin@news.com.au