The stainless steel-encased tissue box is not a good sign.

Lilian Gumerove knew her Bronx heart wouldn’t be able to withstand what she was about to see, so she grabbed a couple of sheets as she headed into the small theater.

Not going in wasn’t an option: She’s a New Yorker.

And, as Gumerove had predicted, when she came out of “Running Toward Danger” about 10 minutes later, she was flustered and crying.

The short film — one of the central exhibits in the Newseum’s gallery about the Sept. 11, 2001 attacks — is an intense step back in time to that harrowing day. The film uses dramatic footage of the hijacked plane crashes, collapsing towers and first-person accounts from journalists who, unlike most folks that day, ran toward Ground Zero, not away from it.

It’s not for the lily-livered. A sign on the wall reads: “Warning: Some material in the film may be too intense for young children.”

Most visitors to the Newseum see at least part of the gallery, said Cathy Trost, the director of exhibit development. That’s no small feat when you think of how many brighter, flashier exhibits (such as a 4-D movie or a chance to try out being a television anchor) the museum has to distract visitors.

“People have really responded to it,” Trost said. “It’s crowded all the time.”

The only change to the exhibit since it opened along with the rest of the Newseum in April has been the addition of those tissue boxes flanking the entrances to the video portion.

The focal point of the moderately sized exhibit is the upper section of the 360-foot antenna mast from the World Trade Center’s North Tower. There’s also a concrete slab blown off the Pentagon and a piece of debris from United Flight 93, which crashed in a rural Pennsylvania field. Visitors can also see a video tribute to Bill Biggart, a photojournalist and the only journalist to die in the attacks.

Newseum staffers are quick to emphasize that the Sept. 11 gallery is not a true memorial. Go to Ground Zero, the Pentagon or Shanksville, Pa., for that. A stop at this exhibit, they say, is meant to teach the challenges of journalism.

But that doesn’t stop the flow of emotions the gallery invokes from its visitors.

Trost noted that museum-goers have already filled up 10 comment notebooks. The remarks left by people who have written in the current edition show that the attack still elicits profound emotions. Few comment on the exhibit itself. Most use the book as a forum to express their sadness and outrage at the attacks themselves:

“Sobering and powerful — we must never forget what happened on 9/11 and how our country pulled together in strength — and fear.” (Shelley Rose, Michigan)

“Remembering 9/11 makes me very sad. Even writing and thinking about it makes me feel sad. God bless America.” (Christian, 13, Washington, D.C.)

“Too many people are starting to forget.” (J. Bubon, Fairfax, Va.)

“Those bastards.” (John Busch, Garland, Texas)

Walter Carter of Chester, Va., noticed the tissue outside the screening room. “Very appropriate,” he said.

“In some ways it’s not graphic enough, if you want the true story,” Chester said. “The thing is, you realize that’s not debris falling — that’s people.”

Alicia Mendonca, 40, of Atlanta, said, “I had to stop watching the film because I didn’t want to spend the rest of the day crying.”

After her strong reaction to the film, Gumerove said simply, “New Yorkers don’t ever forget this. … I don’t know if other people can understand it far away, if you’re living far away.”

“Sure, they can,” her husband, Robert, said.

Journalists, it seems, are moved in a personal way.

Deidra Lemons’ background as a reporter almost made it harder for her to absorb the exhibit in 2008 than the actual events in 2001.

“When you’re a reporter, you make it something that happened to other people, and so you’re capturing their moment in history,” said Lemons, 28, of Montgomery, Ala. “But when you see it, you’re capturing your own moment. So it’s a little bit different. You feel it a little bit more. And it changes your reaction. It’s overwhelming to look at this.”

“I won’t — I can’t even look at those pictures now. See this?” she asks, voice cracking, pointing to the antenna mast. “It’s a lot.”

On the day this reporter explored the gallery, a fieldtrip chaperone shepherded several dozen 10-year-olds away from it — despite the pleas from the aggrieved preteens who wanted to see “the cool twisty thing.”

It’s not uncommon for school groups of younger kids to bypass the Sept. 11 gallery, Trost said. They have little memory of the attacks or appreciation for how they altered the course of this country.

High school students, on the other hand, typically have vivid memories of the 2001 attacks and appreciate the opportunity to revisit it with new perspective.

Timmy, a 16-year-old Woodberry Forest boarding school student whose mother asked that his last name not be used, remembers the attack vividly — even though he was 9 and living on the other side of the Atlantic, in Germany.

“The atmosphere here, it’s — tension,” he noted as he stared up at the crumpled antenna mast. “It’s quite scary to see that thing. I wasn’t here then, but it comes nearer and nearer. It does scare me.”

The seven years that have elapsed since the attack are distance enough for Lemons, the former journalist, to make a tragic new comparison. “It’s kind of like going to the Holocaust museum,” she said. “When you read about it or you learn about it, it’s different when you hear a real survivor’s story or you look at their pile of shoes.

“It’s almost like looking at their shoes. This is their imprint. That’s hard.”