Skywire Live,” Discovery’s airing of high-wire walker Nic Wallenda’s stroll across the Grand Canyon, was a massive undertaking: Performed in the desert with no infrastructure, producers had to build roads and truck in around 200 crew for a one-off event that could have ended with the death of its star.

“We were prepared,” recalls Howard Swartz, VP of production and development for Discovery, and an exec producer on “Skywire.” “We had scripts prepared for our hosts. We rehearsed almost to having a muscle memory of how we’d get away from certain shots, so we wouldn’t show anything that would be disturbing to viewers.”

Tragedy was a very real possibility for “Skywire,” but so were big ratings, with Discovery drawing in around 13 million viewers.

Reality TV has always relied on armchair adventurers for ratings. Early on, it was enough to stuff a house or an island with complete strangers and film them going at it. But in the years since, reality TV has become a regular, relatively inexpensive schedule-filler for dozens of networks — and what juices viewers and ratings has shifted considerably.

Today, some of TV’s most popular unscripted series often rely on derring-do by their cast in high-risk jobs or lifestyles, and that has led to the return of super-risky, one-off “event” TV shows like “Skywire.” Both types of shows have emerged as go-to programming for execs eager to snag premium (that is, live) ratings and provide viewers with a vicarious rush, while in the process hoping to get a brand boost from the buzz.

“There’s been a huge proliferation of cable networks, many of them chasing the same kinds of shows,” says Dirk Hoogstra, exec VP and general manager for History and A+E Networks. “It’s probably the most competitive marketplace I’ve ever seen, and it’s hard to find new hits. You have to zig where everyone else is zagging.”

“The ‘event’ reality show trend indicates how saturated the market is,” says Florida State U. associate professor Leigh H. Edwards, author of “The Triumph of Reality TV.” “Producers are trying to stand out by turning to the adrenaline-junkie appeal of more extreme situations.”

Working a live element into any show is key for networks. Ratings that incorporate DVR playback (up to seven days) are slowly becoming more relevant to the overall perception of a show’s success, but the same-night numbers are still perceived as the real yardstick that shows are measured by.

That leads producers to try and come up with live programming stunts, no matter how little sense they make to a reality series. Veteran Bunim/Murray producer Jon Murray says they are always trying to think of ways to make even “Project Runway” a must-see destination.

“There are conversations at the start of each season about how we can get viewers to watch the show live,” he says. “Those are conversations that have ramped up over the years, especially as we’ve seen people use DVRs to shift programming. Networks are still interested in programs that will get viewers to show up and watch it live.”

That desire bleeds across every kind of reality show; Murray would like for “Runway’s” finale to air live from Fashion Week, while Discovery’s senior exec producer David Pritikin says he’d like to find a way to make “Deadliest Catch” air a live episode.

Networks like History and A&E haven’t quite found a way to climb on the big live-event bandwagon yet, but there are plenty of reality series that draw a similar audience, one looking for scenarios where danger is not just a possibility, but likely.

History’s “The Curse of Oak Island” is about treasure hunters looking for 200-year-old booty, but there’s still the possibility of seeing someone placed into a threatening situation.

“We don’t hope someone gets maimed or dies,” says exec producer Kevin Burns. “But the island has a curse: It says seven must die in pursuit of the treasure for it to be revealed, and so far six have died. So there’s a lurid interest in who will be next. We prefer the audience to think about that.”

But getting voyeuristic audiences to come back every week to a reality series isn’t just about the element of danger, says Pritikin. “The danger genre doesn’t work on its own,” he says. “You need the larger-than-life, compelling characters that drive the story. That said, there’s nothing interesting about a show about danger that has no opportunity for real danger.”

Where reality series will always have it over the one-shot reality event is in the lasting value. In most cases, a live event is a pure shot of adrenaline for ratings and for making the network buzzworthy. Once it’s over, there’s no back end — no reruns, and virtually no sequel potential. The best a network can hope for is that the echoes of what’s been done have helped to cement the brand in audiences’ minds.

“The rewards for us are that we’re delivering on who we are as a brand,” says Heather Moran, exec VP, programming and strategy, for National Geographic, which aired “Live From Space” in March, featuring a trip around the world by the Intl. Space Station — an interesting oddity with pretty much no risk, but very much targeted to the channel’s viewers.

That hasn’t stopped other networks from plotting their next big event moves, though recently Discovery had to re-think what would have been a base jump off of Mount Everest after a deadly avalanche.

Still, says Swartz, “That doesn’t dissuade us from looking at programs with risky elements to them, a long as those programs are smart and we’ve done due diligence.”

In the end, says NatGeo’s Moran, series remain king when it comes to retaining viewers. “People really want to see others exploring, so when we’re able to execute that with events, it’s rewarding for us and the viewer,” she says. “But people really do invest in characters in a series — that’s what brings them back week after week. And it does it in ways you couldn’t by jumping from event program to event program.”