Competitors have been training for months in preparation for the contest, which will see them carry heavy weights, run up stairs, crawl, run and swing a hammer – all while wearing their heavy and constricting fireproof gear.
Michael Weiß, a 27-year-old firefighter from Göttingen, demonstrates how tough the event is.
Setting off at a sprint with two heavy hoses under his arms, he races the first few metres before the burden begins making itself felt. Weiß struggles for breath from under his suit.
"Weiter, weiter" [further] shout German spectators, while English speakers stick with "go!"
There's a babel of different languages at the Interschutz rescue services convention, with participants from Scandinavia to South Africa, India to eastern Europe, there's a feeling of comradeship or even family about the event.
These are all rescue workers who put their body and soul into their work, but that doesn't mean they're shy of a little competition.
"We think we've got a good chance," South African team leader Marc Smith said after his men linked arms in a rugby-style ritual.
Originating in the USA, the "Toughest Firefighter" is a mixture of athletic contest and mass spectacle.
Participants need strength, co-ordination and conditioning to recover and rescue human-sized 80-kilo dummies or haul heavy canisters into the second floor of a building.
Then there's the obstacle course featuring climbing walls, narrow crawl spaces and a race up the 65-metre Hermesturm [Hermes tower, a Hannover landmark] in full gear.
"These are exercises that we often experience in our daily lives as firefighters," said Joachim Posanz, another Göttinger and the first German ever to win the title, when South Korea hosted the spectacle in 2010.
While he doesn't think he'll be on the podium come Saturday, his colleague Andreas Meyer is in pole position going into Thursday afternoon's events – although reigning world champion Lukas Novak from Prague is still in the running.
"Of course it's not something for everyone," Meyer said. "But the sporting aspect, always pushing at your own limits, that fascinates me."
Last year, Meyer pushed a little too hard and ripped his Achilles tendon while training.
"That was really harsh," he admits, although "this time it went perfectly – I've managed a comeback."