How is a firefighter to know that a 110-story building has collapsed in front of him?
For Rudy Sanfilippo, a retired union representative for Manhattan's 2,000 firefighters, it is just one of those things that only someone who was there can understand.
As with just about everyone else's story, Sanfilippo’s Sept. 11, 2001, started utterly mundane.
He was having a union meeting at a diner in Queens when "I got beeped," he said in his matter-of-fact, classic "New Yawk" accent.
A plane had hit the World Trade Center.
Alarming, for sure, thought Rudy, but it was not all that unusual for small planes or helicopters to slam into Manhattan skyscrapers.
As he headed across the Triborough Bridge, he heard on his fire department radio about a second crash.
"When the second plane hit, I knew something very wrong was going on. It was beyond comprehension. From the moment we heard about the second plane hit, we knew we were under attack."
Combined with reports of other planes crashing into the Pentagon and a field in the state of Pennsylvania, but with no other information available, "All you could use was your imagination," he said. "What the hell is going on? Is this World War Three? Is the whole world at war?"
Sanfilippo was one of the first to arrive at a command post that had quickly been established at the South Tower as it burned, but "it was impossible to wrap your head around it."
"Two major fires and a lot of people to be evacuated," as he shuttled between the lobbies of the two towers, directing incoming traffic of first responders.
"Communications were poor, there were no water supplies to fight the fires, pipes had been damaged or disabled," he said.
Sanfilippo mentions something that tears at hearts to this day: "People started jumping (to their deaths) -- hundreds of people, not the three or four that you might be aware of from news stories, a steady flow of people jumping."
Eventually, even as the world watched the South Tower fall first, Sanfilippo was not aware of it from his spot in the North Tower.
"When the first building went down, and even after it went down, I was not aware that building had collapsed," he said, "In the fire service in New York City, it's not uncommon that there's so much smoke that you can't see a certain level of a building. You just can't see past the smoke."
But he knew the North Tower was coming down.
Five or 10 minutes before the collapse, Sanfilippo said he did not see any civilians. He did see one firefighter about five minutes prior, the last firefighter he would see, "waving his arms, telling me to get the hell out of there."
But he stayed because "we got guys here."
For a moment, there was "an unbelievable silence,"
"Then all of a sudden, I noticed the sound, it was earth-shaking ... the boom, boom, boom, of each floor was incredibly loud.”
"And everyone was already gone," either dead inside the building or safely away from it.
"Virtually all of the first responders that survived, we all had drawn the same initial conclusion that the building was going to topple (over). We were not familiar with the physics that would force the building to come straight down, pancaking."
As the building fell, his only thought was "Well, I'm not going to outrun this, so I'll head north, and we'll see what God does."
Was he as "matter-of-fact" about it in that moment as he is today?
"I was," he said. "At the same time, you're in utter shock. The whole thing was very cartoonish. In other words, it was almost as if you were observing it as opposed to living it. I concluded that was shock. We were working through shock."
"I was one of the very last people to actually walk away." Except it was not exactly a walk. The wind gust that accompanied the collapse, estimated at hundreds of miles per kilometer, knocked him to the ground.
He headed north in "complete and utter darkness, except for things glowing, like molten metal." He followed a line of fire trucks along the street and finally came to the end of the dust cloud about half a mile away.
"I'm breathing in (expletive) that I coughed up for days afterward." He would later lose part of a lung from a rare cancer that he presumes he contracted from the dust.
For a while, he tried to console the drivers of the firetrucks, those whose job it was to stay inside the truck at all times.
"There were in shock," he said. "They just realized that their (fire) companies were gone."
Later, he walked back to ground zero and remembered the surreal sights, like a jet engine sitting on a sidewalk, and cars stacked on top of each other, pressed against a building from the blast.
Sanfilippo’s job as the union trustee was to coordinate the help his firefighters would need to get back on their feet. The final death toll for the New York Fire Department would be 343.
He visited as many families and attended as many funerals as he could, around 150, but "by the first weekend (after 9/11), I realized the bodies were coming in too fast."
He finally gets choked up, thinking about it.
"I can't believe this is still hard to talk about, it's been so long."
Sanfilippo said he went into a "hyper-vigilant" stage, working 20-hour days, getting countless calls from firefighters looking for psychological help.
"Guys were flipping out," he said, but at the same time, his union infrastructure had fallen apart.
Later, he and other union representatives tangled with city officials who, according to Sanfilippo, wanted to end the digging at ground zero too soon, so they could begin work on a new construction site.
"We knew that (the diggers) were still coming up with bodies and parts of bodies. We knew that it wasn't time yet to leave."
Ultimately, the firefighters won. "We stopped (the city) a gazillion times."
The digging finally did come to an end in April 2002 and Sanfilippo is satisfied that firefighters did as much work at the site as they could. He was there the night that the very last shovel of identifiable dust was taken out.
Slowly, 9/11 started to lose its iron grip on Sanfilippo. He gets choked up again and pauses, talking about a night at his dinner table about 18 months after 9/11.
"One of my adult daughters just said to me, 'Welcome back.'"
"Apparently, I didn't see it in myself, but I had what came to be known as 'the thousand-mile stare,' where you were just so distracted, you weren't even aware of other things that needed to be done. I realized I was drifting."
Sanfilippo and a lot of his fellow firefighters went to therapy, which helped, he said, but his takeaway, 20 years later, is disappointment.
Sept. 11 should have been a unifying event for New York's first responders and city officials. Instead, "it was very disappointing, the way it was politicized. It's sad."
For years afterward, Sanfilippo would give speeches at 9/11 anniversaries to honor the fallen firefighters. He usually gets a bit melancholy in the days leading up to the anniversary and he still occasionally has dreams about it.
But this Saturday, the 20th anniversary of 9/11, he will happily be attending a college football game with his daughter and his grandchildren, as far away as possible.
He cannot wait.
"I gotta move on," he said.