NEW YORK — There are prominent videos of the twin towers collapsing, photos of people falling from them, portraits of nearly 3,000 victims and voicemail messages from people in hijacked planes.

But behind the wrenching sights and sounds of the National Sept. 11 Memorial Museum lies a quiet effort to help visitors handle its potentially traumatic impact, from silent spaces and built-in tissue boxes to a layout designed to let people bypass the most intense exhibits.

Discreet oak-leaf symbols denote items connected to the dead, and the images of falling victims are in an alcove marked with a warning sign. Designers made sure rooms have ample exits, lest people feel claustrophobic in the underground space. And American Red Cross counseling volunteers stood by as the museum opened to the public Wednesday.

“There’s a lot of thought given to the psychological safety of visitors,” said Jake Barton, who helped create the exhibits.

It didn’t seem like enough to Lori Strelecki, who was among the first people to tour the museum Wednesday. She said she had seen a visitor crumpled over, crying.

“Is that something you want to evoke?” asked Strelecki, who runs a historic house museum in Milford, Pennsylvania. “It’s too much.”

Dr. Steven Cennamo, a New Jersey dentist, was impressed by the museum’s blend of spaciousness and artifacts as intimate as a victim’s wallet. Given the singularity of 9/11, “I don’t think you can overdo it,” he said.

More than 42,000 9/11 victims’ relatives, survivors, rescuers and recovery workers have already visited the museum, which opened to them last Thursday, Executive Director Joe Daniels said.

It’s the latest in a series of memorials-as-museums that seek to honor the dead while presenting a full, fair history of the event that killed them. And the Sept. 11 museum strives to do that at ground zero while the attacks are still raw memories for many.

Museum planners realized early on the challenge of trying not to shatter people “while at the same time being true to the authenticity of the event,” said Tom Hennes, founder of exhibit designer Thinc Design.

Trauma specialists told museum leaders that sounds of voices and images of hands and faces could be particularly distressing and that visitors should get to choose what to see.

The goal: “to keep it feeling alive and present without making it so alive and present that it’s unbearable,” says psychologist Billie Pivnick, who worked with Thinc.

To allow visitors an emotional breather, silent spaces with few artifacts surround the densely packed historical exhibit that follows the timeline of 9/11, set off by a revolving door. Elsewhere, a room where visitors can call up recorded recollections about individual victims was designed as a quiet sanctum for feelings, with tissue dispensers embedded in the benches and acoustically padded walls, Hennes said.

The historical exhibit, crafted by another firm, Layman Design, envelops visitors in images, information, objects and sounds, but designers sought to avoid emotional overload.

Ambient sounds of emergency radio transmissions and victims calling home are interspersed with the calmer tones of survivors recounting the day. The hijackers are included, but carefully, in grainy airport-security video and unobtrusive individual photos.

Still, the display doesn’t shy from large projections of the towers crumbling. “It’s a dramatic presentation, but I think it’s a dramatic moment,” explained Barton, whose firm, Local Projects, handled the multimedia components.

Other museums have faced difficult choices presenting the horrors of history.

The U.S. Holocaust Memorial Museum in Washington, for example, decided to display photos of hair shorn from people in death camps, but not the hair itself, and ensconced some graphic film footage in walls too tall for children to see over.

Beyond content choices, the Sept. 11 museum hopes a human touch can help visitors grapple with their reactions.

Retired social worker Georgine Gorra helped people find their way around the museum after Thursday’s dedication ceremony. They didn’t seem traumatized, she said, just tearful.

“We all were, frankly.”