WASHINGTON -- It was a tough moment for Charles Samuels, the director of the Federal Bureau of Prisons.

At a hearing on solitary confinement before the Senate Judiciary Committee on Tuesday afternoon, Samuels, who has been at BOP since 1988, struggled to answer a basic question put to him by Sen. Al Franken (D-Minn.).

“How big is an average cell in solitary?” Franken asked. "Thisdecad is a human thing we're talking about. We've got a lot of statistics; how big is the cell?"

Samuels took about a minute to answer, repeatedly asking Franken to clarify the question.

A frustrated Franken turned to the crowd: “Am I asking this wrong?” On a day when Piper Kerman, the author of Orange Is The New Black, and Damon Thibodeaux, an exonerated former prisoner who served 15 years in solitary, both testified on the devastating toll exacted by solitary on the human psyche, the former SNL writer elicited a rare laugh.

Eventually Samuels said that the average prison cell was 6 by 4 feet, which if true would mean that many prisoners would have to serve their time without fully lying down. Later, he revised the dimensions to 12 by 7 feet.

To see the full exchange, watch the video above.

"It's disturbing that Director Samuels wasn't able to answer such a basic question about the Bureau's use of solitary confinement," ACLU National Prison Project Director David Fathi said in a statement to The Huffington Post.

A BOP media representative did not respond to HuffPost's request for comment on why Samuels had so much trouble answering Franken's question.

Samuels' lack of knowledge stood in contrast to Colorado official Rick Raemisch, who also testified at the hearing.

Raemish, the executive director of the Colorado Department of Corrections, recently spent a night in solitary confinement to learn more about the practice, according to an opinion piece he wrote for The New York Times.

In the piece, he posed a question of his own: How long would he be able to stay in solitary without going insane?

“I don’t know,” he wrote, “but I’m confident that it would be a battle I would lose.”