When thunderstorms slammed New York's Central Park before this summer's highly anticipated Black Eyed Peas concert, officials made the rare decision to call off the event. Tens of thousands of fans were livid, but safety experts praise the decision for bucking the industry's aversion to such last-minute cancellations.

As the multi-billion-dollar outdoor concert business has evolved from little more than shows under a canopied stage to productions featuring up to 20 tons of lighting and video equipment, experts point to the Indiana State Fair's fatal stage collapse and several similar accidents as evidence of the necessity for caution — and regulation.

"It's the Wild West when it comes to standards and guidance and consistency," said Paul Wertheimer, founder of the consulting service Crowd Management Strategies. "People from place to place can do whatever they want."

Concert mayhem is neither new nor unique. Eleven people died as crowds pushed their way into a 1979 The Who concert in Cincinnati. The Indiana collapse that killed five people and injured dozens of others Saturday, when powerful winds toppled a huge stage onto an audience awaiting Sugarland show, was among several more recent incidents.

What's changed over time is the size of the events and pressures on promoters.

Academy of Country Music CEO Bob Romeo, who has more than three decades of music promoting experience, remembers when the first stage tops were built simply to provide shade from the sun. Now, as productions expand to include massive video equipment and up to 40,000 pounds of lights, Romeo says he has to balance safety concerns with putting on the best possible show.

"Any promoter you would talk to that's done outdoor shows probably saw the video of what happened in Indianapolis and said, 'That could be me. That could be any of my colleagues.' At one time or another, if you do enough outdoor shows, you are going to face those scenarios," he said.

Romeo said he decided last year, when the televised ACM Awards found it needed to accommodate more fans than its MGM Grand event space in Las Vegas could hold, to go with additional indoor space at Mandalay Bay.

"Whenever you're outside, there's a risk. It just is. It's an inherent risk. It's been in the fair and festival business from day one," he said. "I think what you saw happen in Indianapolis was just a tragic event we try to prepare for as best we can."

With album sales dwindling and record companies struggling, artists depend on concert ticket sales and merchandising to boost their bottom line more than ever. Revenues for the 100 top-selling North American tours were $1.1 billion for the first half of 2011, a rise of 16 percent following lackluster sales in 2010.

Promoters say they can't disappoint the fans who buy those tickets.

"There's an expectation," said Jacob Worek, who runs Portland, Ore.,-based Event Safety Consultants. "If you're going to spend that money, you're going to be given a bigger show."

U2's 360 Tour, which featured a massive revolving stage with claw-like legs and a gigantic video screen behind the band, was one of last year's top-grossing concerts. The stage took days to set up and tear down and involved more than 100 semi-truck loads of equipment. Tickets ran upward of $250.

The expansive approach has extended to music festivals nationwide.

Over 20 years, Lollapalooza has grown from a 1-day amphitheater event to a 3-day festival featuring more than 130 bands and artists on stages in a downtown Chicago park. The festival grossed more than $21 million last year and drew a record 270,000 people this year with headliners like Eminem and Coldplay.

But even smaller festivals feel the crunch.

"Bigger and better is what everyone wants, and more elaborate," said Jack Hammer, executive director of the Three Rivers Festival in Fort Wayne, Ind., a nine-day event that includes rides, games and concerts. One show there drew about 7,500 people last month.

Safety regulations, experts say, haven't kept up the pace in part because they aren't standard. No single government agency oversees or sets rules for outdoor concerts, leaving a range of guidelines across events.

The Indiana State Fair had a one-page emergency plan with only general bullet points and fair officials aren't sure whether anyone is supposed to inspect stages. No one inspects the stage at the Three Rivers Festival. Chicago, meanwhile, has some of the strictest standards in the country and requires outdoor events — including Lollapalooza and Pitchfork — to pass the city's building codes, have a wind gauge on stage and provide a "high wind action plan" for what organizers will do if gusts go above 30 mph.

Still, organizers and host cities cite improvements available to events that seek them out. For example, updated weather-tracking technology can give festival and fair organizers warnings well ahead of hazardous storms.

When Oprah Winfrey closed down Chicago's Michigan Avenue in 2009 to film her season premiere with a performance by the Black Eyed Peas, the stage was equipped with not only a wind gauge but a full on weather center.

Indiana State Fair officials acknowledged Wednesday that the fair did not follow its one-page severe weather emergency plan before Saturday's collapse and that fans should have been told that the National Weather Service had issued a severe thunderstorm warning.

Alan Morgenstern, who owns Morningstar Productions, a Southern California-based company that has provided stages for musicians like Billy Ray Cyrus and events like Comic-Con, said more attention needs to be focused on keeping people on or near stages safe as they continue to grow.

"The guys who work for me are extremely careful and take time to go the extra mile for safety, and I think that's the key," he said. "You really have to think that when you're putting something over people's heads, it's got to be safe."

The Black Eyed Peas announced Wednesday that their canceled charity show will be rescheduled for Sept. 30 in Central Park.