SEATTLE — As I reached the 50th floor in the stairwell of the Columbia Tower on Sunday, it became clear that I’d underestimated the situation.

I sat down in a small stairway alcove and considered the possibility of giving up. Firefighters passed me, one by one, most offering a thumbs up that was both a question and a form of encouragement.

I nodded and answered each silent “Are you okay?” question with my own quivering, not entirely truthful thumb.

I didn’t require medical assistance, but the air in my tank was long gone, I was overheating, and the 50-pound pack on my back was causing unbearable back and neck pain. The finish line of the Firefighter Stairclimb remained 23 floors away.

It might as well have been a stairway to Mars.

I answered three more questioning thumbs with more lies.

I was not okay.

When accepting an invitation from the Everett Fire Department to ascend the staircase of Seattle’s tallest building, I knew I was no hero.

I’m a sportwriter. I go to games and watch people play. These people respond to emergencies and save lives.

As a firefighter stopped and asked if I was alright, I felt like something from a different species than the physical specimen assessing my well-being. Released to climb the stairs from the starting line in 10-second intervals, I’m not sure how many firefighters passed me by on the way to the top. Perhaps enough to take on a small natural disaster.

They sped on, some taking two steps at a time, in full turnout gear, racing to the top to raise funds for Blood Cancer United (formerly the Leukemia & Lymphoma Society). For the 35th year, thousands of firefighters spent their day off in the stuffy, monotonous, seemingly never-ending Columbia Tower stairwell. This year, nearly 2,500 firefighters from 317 departments across 28 states zig-zagged upward at the annual event. Hundreds of additional people volunteered their time throughout the day.

Why on Earth participate in something like this?

The Firefighter Stairclimb has raised roughly $30 million since 1991, including over $2.4 million so far this year alone. Donations are still being accepted at https://pages.lls.org/events/wa/firefighterstairclimb26 to raise funds for Blood Cancer United’s mission of blood cancer research, patient support and advocacy.

Selfishly, curing cancer was not top of mind for me on the 50th floor.

“You got this,” a passing firefighter called out to me through his airmask, slapping me on the back of my fire-resistant gear, which compounded every degree of body heat and drop of sweat from my failing, 54-year-old body.

I returned the airtank pack to my back and threw on the helmet I’d borrowed from Mike Dunmire, the captain of an Everett Fire climb team that has raised over $1 million since 2000.

I advanced two floors that felt like 10, and my neck and back started seizing again. More pats on the back and fistbumps, and a few more left me behind.

Many of these men and women are very fast.

Miles Farrow-Johnson of the Bellevue Fire Department made it up the 1,356 stairs to the 73rd floor in 11 minutes, 53.56 seconds, the fastest time this year in the “fire division,” which requires full gear. Forty-five reached the top in less than 15 minutes.

While I knew that was quick, I had no idea — absolutely no clue — what incredible shape people like that are in.

I’ve participated many times in Big Climb Seattle, a Blood Cancer United event two weeks after the Firefighter Stairclimb, which is open to all who wish to ascend to the top of the tower. I typically finish in the middle of the pack at the Big Climb, with a personal-best 15:29 two years ago. I trained over the past month or so with a 45-pound weighted vest, preparing my legs and back for extra weight I’d have to carry up the stairs in my first Firefighter climb. The protective turnout gear — referred to as bunks — would be an issue, I knew. Designed to keep fire and heat away from skin as much as possible, it also keeps in body heat.

I figured the Firefighter Stairclimb would be three times harder than the Big Climb, and set a goal of finishing in under 45 minutes. I thought I was setting a low bar for myself.

Boy, was I ever wrong about that.

I held myself to a slow pace, knowing that if you go out too fast, you are cooked. With those bunks on, I mean that almost literally.

When I reached the 35th floor, my back and neck started cramping. The training vest had been too balanced and too comfortable. My neck, barely accustomed to supporting the weight of a baseball cap, could not handle the 3-4 extra pounds from Dunmire’s helmet — in part because I was leaning over to grab the stairway’s arm rails like a heavyweight boxer on the ropes.

Meanwhile, the shorts and T-shirt inside my borrowed bunks were no drier than if I’d jumped into the Snohomish River and floated into Port Gardner Bay.

After my rest at floor 50, I resumed the climb. Two stories later, my neck and back seized up again.

“You can’t quit on the 52nd floor,” I said out loud. “If you were going to quit, it should have been 30 stories ago.”

Two more floors, more seizing, followed by a series of pats on the back and fist bumps.

Eventually, I started carrying the helmet, which calmed my neck. I reach the 60th floor, which is where many start to falter. I could hear wretching, and several firefighters were doubled over with exhaustion. I gave a few pats on the back of my own and stumbled up the final 13 floors, one very slow step at a time.

The last two floors, I moved as quickly as I could, which was a speed just slightly faster than lying down. Volunteers at the top shouted words of encouragement as I closed in on the finish. They treated me like I’d won the Boston Marathon.

As I entered the Sky View Observatory on the 73rd floor, I was greeted by what felt like a NASCAR pit crew. They pulled off all the pieces of gear that had made me miserable for the past hour-plus, but insisted that I keep moving. With thousands climbing that day, they worked to prevent me from creating a bottleneck at the top of the stairs.

After hydrating and sitting in a chair at the other end of the observatory for a few minutes, I walked to what felt like humankind’s greatest invention — an elevator.

At the bottom, I was met by several Everett Firefighters who made me, of all people, feel like a hero. They thanked me for walking in their boots for part of a day. I ran into D.J. Neyens, an Everett battalion chief who climbed despite being in the midst of chemotherapy treatment for multiple myeloma, a type of blood cancer he’d helped raise money to battle at Firefighter Stairclimbs years before his own diagnosis.

The man fighting for his life asked me how I was feeling before I could ask him the same question.

“That was awful,” I said. “Amazing, but awful.”

He explained to me that the climb was hard this year. It wasn’t until later that I realized that, despite chemo’s side effects, the former minor league catcher had finished in 20:32.44, easily in the top third of climbers in the fire division.

Another Everett firefighter, Zack Greenberg, paced the lobby, angry with himself. He’d started too fast, ignoring former stairclimb winner Brett Molsberry’s mantra of “Go way slower than you think you should.” He’d tried to keep up with another competitor and burned out too early.

“There’s always next year,” he said.

Still, he finished this year’s climb in 19:59.81.

Dunmire, who became a father two weeks earlier and entered the event conceding that he was going to be slower this year, told me he was thrilled with his climb. Though his training time had been limited in recent weeks, he finished in 18:29.60.

Mercifully, because I was not an official entrant into the event, my time was not recorded. It was approximately 70 minutes, which would have been good enough for 1,903rd place out of 1,916 in the “fire” division.

I joked with an event volunteer that I was the worst firefighter in the history of fire, but he reminded me why everyone was there on Sunday.

“It’s all about the cause,” he said. “And finishing is an accomplishment.”

For the first time that day, I offered a sincere thumbs up.