RIO DE JANEIRO—The globe’s biggest Carnival bash opens Friday, and it promises to be an even bigger blowout this year, with 20 per cent more tourists expected than in 2011.

Rio officials say they’re also better prepared to keep the chaos under some semblance of control, with more portable toilets, traffic guards and paramedics, as well as a new central command centre monitoring it all.

“We want revellers to be conscious that they can party but also care for the city’s public spaces,” the president of Rio’s tourism department, Antonio Figueira de Mello, said in a statement.

About 850,000 tourists are expected during the raucous, five-day free-for-all that kicks off when Rio’s mayor hands the key to the city to rotund King Momo, the mythical jester figure who reigns over Carnival.

Merrymakers are expected to spend $640 million and generate 250,000 jobs, according to the city’s economic development department. But the world’s biggest party traditionally leaves a hangover to match: last year, the weeklong romp left about 850 tons of trash strewn around town.

Rio officials have dispatched 80 mobile medical emergency units, 1,000 traffic guards and 15,000 toilets around the city and officials are running a campaign against urinating in public. Rio residents are humming along with a catchy little samba running on TV, telling partiers, “If you want to pee, don’t do it here, don’t do it here.” The jingle rhymes in Portuguese.

Rio also launched a smartphone app, free for iPhones and Androids, that tells visitors in English, Spanish or Portuguese where to go for blocos, the roving samba bands that draw millions, pied-piper style, through the streets, as well as basic information on public transit, eateries and museums.

The federal aviation authority expects 3 million people to shuttle in and out of airports during Carnival week, 13 per cent more than last year. Airports taking in visitors will also have 30 per cent more federal police, and workers with “May I help you?” vests will be circulating to take care of visitors’ last-minute questions.

Helping this notoriously gridlocked city tackle the street closures, mass gatherings and parading parties is Rio’s new central command centre, which the city hopes will be a key to keeping order when Rio hosts the 2014 World Cup matches and the 2016 Olympics.

It has been fully operational since November, but this is the first big test of the command centre’s ability to keep the city running during a large event.

“The centre was created to work during great events, minimizing the impact they have on the daily routine of residents,” said Savio Franco, who heads it.

It was in this centre, which takes feeds from more than 500 cameras spread around the city, that the routes of Rio’s more than 400 roving street parties were plotted out, along with the points were guards, medical units and toilets would be placed. Once the party is in full swing, the action can be monitored in real time, allowing the city to respond immediately to any problems, Franco said.

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With all this planning, he said he’s hoping maintaining control of Carnival should be a cinch.

“There will be more than 5,000 city government workers involved in making this party go as smoothly as possible for cariocas and for the tourists,” France said.