- Sunday’s fire, which came from fuel in a tanker truck under the overpass, is estimated to have burned as hot as 2,000 degrees Fahrenheit, one expert said.
- On Monday, Pennsylvania Gov. Josh Shapiro issued a disaster declaration, allowing the state and city to draw down federal funds to begin the reconstruction.
- A lot still has to fall into place for a quick completion, another expert said, including having the money, workforce and materials needed.
The collapse of an I-95 overpass Sunday morning in Northeast Philadelphia is a real-life physics lesson, the result of what happens when building materials come in contact with intense and prolonged heat.
Steel girders used in bridges can lose 50% of their strength at about 1,100 degrees Fahrenheit, while concrete loses about half its strength at approximately 950 F, according to Andrew W. Herrmann, past president of the American Society of Civil Engineers.
Sunday’s fire, which came from fuel in a tanker truck under the overpass, is estimated to have burned as hot as 2,000 degrees Fahrenheit, Hermann said.
“So with that type of a fire, we are way over what would cause damage to the bridge and actually lead to its collapse,” he said.
The fire, which remains under investigation, caused a partial collapse of a portion of the interstate’s northbound lanes on the Route 73/Cottman Avenue ramp and compromised the southbound lanes leading into Philadelphia. Pennsylvania State Police confirmed Monday night that the body of a South Jersey trucker was recovered from the accident scene.
The collapse shut the interstate in both directions, impacting local traffic and cutting off a portion of the East Coast’s primary highway. About 160,000 motorists travel along the impacted section every day.
Why fire and steel don’t mix
The introduction of steel in our highways and bridges has made them stronger, safer and faster to build. Steel, an alloy of iron and small amounts of carbon, also makes these structures more flexible, allowing them to be built in sites that are earthquake-prone or have high winds.
While these structures are usually stronger because of streel, they remain susceptible to such things as fires — especially fires that give off intense heat and burn for lengthy periods. It took the Philadelphia Fire Department about an hour to bring Sunday’s blaze under control.
While buildings are protected from fire using sprinkler systems and other means, outdoor highways are not, said Hermann. That’s because it would not be cost-effective.
University of Delaware Civil and Environmental Engineering Professor Michael Chajes pointed out things such as freezing temperatures and other environmental exposures.
“But if you had something on a bridge and something happened, it’s very possible it takes out your protective system,” he said
Damages from fires also vary.
For example, Chajes said a tire fire in Philadelphia’s Port Richmond area in 1996 did not bring down a section of I-95 like Sunday’s blaze did. The 1996 fire did cause damage to the interstate that lead to a temporary closure, but drivers were back on the interstate as crews worked for months to reconstruct the roadway.
The current damage is estimated to leave the Philadelphia section of I-95 unusable for months.
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“The difference in the two fires was that fire caused by tires is not going to be as intense and as hot as the fire caused by fuel,” Chajes told Delaware Online/The News Journal. “Similar to the [World] Trade Centers that collapsed, that was jet fuel.”
Chajes was referencing the collapse of two World Trade Center buildings in New York after terrorists attacked the country on Sept. 9, 2001.
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While many initially believed the skyscrapers came down after two hijacked Boeing 767s crashed into them, a report from the National Institute of Standards and Technology found the unusually large number of jet fuel from the planes ignited multi-floor fires, which reached temperatures as high as 1,800 F.
This significantly weakened the floors and columns with dislodged fireproofing to the point where floors sagged and pulled inward on the perimeter columns leading to the buildings’ collapse.
No quick fix for I-95 collapse
On Monday, Pennsylvania Gov. Josh Shapiro issued a disaster declaration, allowing the state and city to draw down federal funds to begin the reconstruction.
“I-95 is a critical roadway that supports our economy and plays an important role in folks’ everyday lives,” Shapiro said on the day of the collapse.
While this helps start the rebuilding of the section, experts say it will take months to fix the interstate which still has to be fully inspected in order to find out the extent of the damage. Though the southbound span of the interstate’s overpass did not collapse, Chajes suspects the lanes were compromised because of the fire’s heat.
“So that section didn’t get as hot, but it got hot enough to damage the steel to the point where it probably needs to be replaced,” he said.
Investigators must now find the extent of the damage and figure out if it needs to be repaired, strengthened or replaced.
Chajes expects the Philadelphia repairs to take months, but he said the speedy rebuilding of Atlanta’s I-85 offers some hope I-95 might be fixed as quickly.
A massive fire in Atlanta in 2017 caused the collapse of an elevated portion of I-85, shutting down the roadway which was used by more than 250,000 people daily, according to the Greenville News. A contractor, working around the clock, was able to replace the roadway in about six weeks.
“Seeing that the Atlanta [project], which was a large section, was done in a few months tells me that you can do something that quickly,” he said.
But a lot still has to fall into place, Chajes said. This includes having the money, workforce and materials needed for a swift completion.
When I-495 over the Christina River closed during the summer of 2014 to make emergency repairs, Chajes said construction workers needed certain rebar that was taking too long to arrive. Construction crews, he said, asked other worksites for the materials in order to finish the $45 million repairs caused when a contractor deposited 55,000 tons of dirt near pillars that shifted the ground, bending underground supports, slowly tipping piers on both the north and south lanes.
“So some of those things come into play in repairing it,” he said, “but I would say you’re on the order of months.”
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Hermann, the past president of the American Society of Civil Engineers, agreed this would take time, adding a lot has to go into this. This includes everything from figuring out what happened to how much damage there is.
After that, they will need to obtain the steel from the mills, where they will take it to a fabricator who will cut and weld the pieces together to make the I beams that will then need to be delivered where crews can start working with them.
So laying out a slab of metal over the damaged area is a no-go, he said with a laugh.
“It’s almost 100 feet,” Hermann said. “That’s a big slab.”
Other roadways, similar problems
Sunday’s collapse is not the first such incident in the United States. Each such calamity brings a set of impacts to local and commercial motorists who navigate the roadways.
The region has experienced previous structure damage, such as when a tire fire in Port Richmond resulted in severe structural damage to a portion of I-95 in 1996.
A section of I-81 near Harrisburg closed in both directions, causing months of delays after a tanker truck fully loaded with diesel fuel overturned in 2013 and exploded into flames, sending black smoke billowing into the sky.
1996 tire fire:Additional detours, closures put in place by Philadelphia Police in wake of I-95 collapse
Harrisburg tanker truck crash:Fiery diesel truck explosion closes Pa.’s I-81
Contact Esteban Parra at (302) 324-2299 or eparra@delawareonline.com.
