Small shackles from the 1800s are among the artifacts that will be on display at National Museum of African American History and Culture. (Smithsonian National Museum of African American History and Culture)

They are heartbreakingly small, these rough-hewn iron shackles with openings that are just 21/2 inches in diameter. They are menacing, too, their five-pound bulk disturbingly heavy for the tiny wrists they confined. Despite their small size, they deliver a gut punch by summoning the horror and humanity of the slave trade in a way that no history textbook could ever do.

The shackles are among the thousands of items that will be on view at the National Museum of African American History and Culture when it opens Sept. 24. These artifacts will tell stories of slavery, Reconstruction, segregation and the civil rights movement. Museum officials anticipate tears, sighs and even some anger as visitors proceed through the galleries.

The visitor experience has been a priority from the beginning, addressed in the design of the building, the organization of exhibitions, and the text and videos that supplement the displays. And now, with less than six months to opening, the effort turns to the front lines, to the staff and volunteers who will interact with visitors.

“Not a lot of (other institutions) are taking on, head on, one of the most difficult things society is facing today, which is the history of our country and how that impacts today,” said Esther Washington, the museum’s director of education. “The idea of letting people sit with a little bit of discomfort is something we have to do because of the stories we have in the museum.”

Louise Lawrence-Israëls knows firsthand about the difficulty of talking about race, identify and social justice. The 73-year-old Bethesda resident is a volunteer at the U.S. Holocaust Memorial Museum, where for 22 years she has encountered a range of responses, from shock to tears to surprise. The work is exhausting — though she doesn’t notice until she gets home after a day of tours or talks.

“It is not tiring for me when I’m doing it. It’s uplifting,” she said. “It’s so important that you can make an impact on people. People just don’t know. It’s baffling how little they know.”

Lawrence-Israëls was a “hidden child” who was not sent to the camps. She says visitors reveal their emotions by grabbing her arm or taking her hand, and they often ask personal questions (“Do you still believe in God?” is a common one). “They can’t believe anyone has survived that,” she said. “It’s too much for them.”

Officials with the African American museum turned to their colleagues at the Holocaust museum and the National September 11 Memorial Museum for advice. They are among some 200 museums in the United States that focus on difficult subjects, from the Holocaust to terrorism to World War II, according to the American Alliance of Museums. Their experts say a critical first step is acknowledging the difficulty of some of the exhibitions and the conversations they will prompt.

“There’s no such thing as harder, or hardest. There’s just hard,” explained Sarah Pharaon of the International Coalition of Sites of Conscience, a network of memorials, museums and historic sites. “This is history that is personal, and creating an atmosphere that allows for people to share their personal truths is vital.”

Design is also critical. Many museums have incorporated spaces for reflection and quiet. The Holocaust museum, for example, includes spaces on every floor and a Hall of Remembrance. The 9/11 museum places its more challenging exhibits in alcoves that can be bypassed and has spaced early exits along the gallery.

“There are visitors who don’t want to have the whole experience. They’ve had enough,” said Clifford Chanin, the 9/11 museum’s vice president of education and public programs. “We’re allowing visitors to make choices within our choices.”

Smithsonian Secretary David J. Skorton praised the African American museum for anticipating the need for visitors to decompress. “The sensitivity of the designers, especially director Lonnie Bunch, the thinking that went into it, even includes some contemplative space, so after being face to face with areas of tragedy or challenge, there is a space for someone to reflect,” Skorton said.

In addition to the contemplative court, an area with skylights and water adjacent to the history galleries, the museum features a series of framed views of the Washington Monument, offering visitors a respite as they weave through the exhibitions. The museum also plans to use red borders on textual explanations that are graphic or violent to alert guests in advance.

Training staff to handle viewer reactions is key. Washington and her team chose volunteers carefully from more than 1,000 applications, seeking friendly individuals who can direct guests to the nearest bathroom but also intuitive people who can spot someone in emotional distress.

They selected about 360 volunteers, most of whom will work for free as visitor information ambassadors and docents. Training takes either four months or nine months, depending on the position.

Washington plans to accompany the volunteers through the exhibitions, giving them the time to discuss them and to process their own reactions. Then they will use role-playing exercises and what-if scenarios to prepare for visitors. “I know in life, conversations are easier if you practice them,” she said.

Washington expects emotional reaction and even anger from the upcoming “Changing America” exhibition, which begins with the death of Martin Luther King Jr. and focuses on everything from the Black Panthers and hip-hop to the election of an African American president and the Black Lives Matter movement. Another polarizing moment might come in the culture galleries, where two objects related to Bill Cosby will be displayed.

This kind of visitor engagement is not easy. Pharaon describes it as “working in a state of productive discomfort” and Washington likens it to physical healing.

“It’s the notion of when you have a wound, the scab has to grow. You have to allow for that stretching and growing before new learning happens,” she said, noting that the museum’s stories of race and identity may uncover these wounds. “That’s going to be one of the difficult things for people, how closely connected almost everything we’re showing is to how people are reacting today.”

Washington is quick to note that there will be much in African American museum galleries that is fun and uplifting. “We’re worried people won’t want to come because they are afraid it’s so depressing and sad and they’ll come away a broken person,” she said. “There’s more than you’re thinking. Just like life, it’s not all sad or all wonderful.”

As much as they are trying to prepare, some of the knowledge will come after the building opens, she added, when her staff will learn to balance helping with watching.

Her colleagues concur. Chanin said there are many tears at the 9/11 museum, and an important skill for staff is to know when to stay back, and when to intervene. “We never want our visitors to feel abandoned,” he said.