Underneath the stage, a little light is brightly shining. It’s not supposed to be doing that.

“You know what?” says Joel Krause, production manager for Arena Stage’s current show “The Great Society,” peering down at the obstinate flame. “I bet we got some blood on it.” Krause suspects a rogue splatter of the crew’s corn syrup-based mixture might be fueling the small fire. It’s the type of thing that can happen when you stage a play full of wounded soldiers, police brutality and peaceful marches that were met with violence.

“The Great Society,” which follows Lyndon Johnson during the later years of his presidency, is set during a turbulent era in America that included the Selma to Montgomery march (and the attacks on participants by law enforcement on the Edmund Pettus Bridge), the Watts riots and the beginnings of the anti-war movement. To represent all that, Krause had to figure out how to deliver riots, blood and fire onstage.

“The starting point is, ‘Oh, my God, they want WHAT?’ ” Krause says of his reaction when director Kyle Donnelly came to him with her needs. “Setting the stage on fire is usually a bad thing.”

After some tinkering, “it very quickly became clear that this is something more than we can do in-house,” Krause says. They called in a New York company, J&M Special Effects, for help. The system they landed on combines gas lines, camping-stove fuel and a crew member, Kyle Handziak, who gets to push all the buttons.

In the space Arena Stage typically uses as the orchestra pit, there are three unassuming black boxes, each of which contains the moving parts for one of three fire effects used during “The Great Society.” The first is deployed after a character throws a Molotov cocktail; the second is used to simulate the smoldering L.A. ruins after the Watts riots; the third generates a roughly 6-foot-high burst of flame that’s part of an anti-Vietnam War demonstration. Off in the corner is a little nook where Handziak sits and sets off each effect.

The effects are fueled by MSR IsoPro, a blend of isobutane and propane. “You buy it at REI,” Krause says. “I called them and said, ‘I’m gonna buy a LOT of this.’ They were probably thinking, ‘What are you doing!?’ ”

Handziak also has a big red button that can shut the whole thing down instantly in case of emergency; in addition, when each effect goes off, two crew members are just offstage with fire extinguishers. The D.C. fire marshal’s office had to sign off on all of it.

“We don’t want to put anyone in any real danger,” Krause says. “We just want it to feel dangerous.”

After the fire comes the blood, which posed its own problems for the crew.

“For the most part, we’ve been using a product called ‘blood juice,’ but it’s corn syrup-based, so once it gets on the [stage] it gets sticky, and you start getting that sticky-sneaker sound,” Krause says. “We’re experimenting with another formula that’s based on laundry detergent, but, not surprisingly, that’s incredibly slick when you put that on the floor. We decided that was a really bad idea.” They eventually stuck with the blood juice (and found a way around the sticky-sneaker sound, judging by its absence during a recent performance).

“The Great Society,” which opened Feb. 2, also requires an immense array of costumes and props, video projections and a set that at one point features a huge number of black combat boots.

“We called everyone to borrow theirs,” Krause says. “Shakespeare Theatre, Round House, everyone. You’re seeing almost every boot in Washington theater.” (Except for the Washington National Opera’s. They were using theirs.)

It’s challenges like these that make a show more interesting, Krause says — challenges like that little light that won’t go out under the stage. As they conduct their pre-show fire test, Krause and three crew members peer down an onstage grate and debate what might be causing the flame. Turns out it isn’t the blood’s fault: Residual gas that had lingered a bit too long in one of the black boxes is keeping the fire burning. After about 30 seconds, the flame finally flickers out. Then Krause is off to make sure everything else is ready for tonight’s show of blood, sweat and fire.

Johnson and Johnson
“The Great Society” is the concluding half of Robert Schenkkan’s two plays about Lyndon Johnson’s presidency, following “All the Way,” which ran at Arena Stage in 2016. This sequel takes place from 1965 to 1968, as LBJ (Jack Willis, reprising his role) has to contend with ongoing pressure for civil rights from Martin Luther King Jr. (Bowman Wright, also from “All the Way”), his desire to pass Medicare and other anti-poverty legislation, rising U.S. involvement in Vietnam and internal threats from his own party, led by Robert Kennedy (John Scherer).

Arena Stage, 1101 Sixth St. SW; through March 11, $50-$99.