The KMG Fire Ball (a.k.a. Afterburner) had a catastrophic breakdown at the opening day of the Ohio State Fair. The simple answer to “What happened?” is: a sweep arm (or something in the junction between the seats and the sweep arm) broke. In response, Fireballs (and Move-It/Spin Out, a related ride with the same gondola arrangement) worldwide have been shut down until KMG and accident investigators figured out exactly what happened.
Several fairs that have contracted carnival companies using the Freak Out (Fireball’s “little brother”) have decided not to allow the operation of Freak Outs, either.
For someone with a grade-school education and a conviction that all catastrophic failures can be prevented with enough qualified inspections, this seems to be a sensible precaution. Actually, it’s a great example of why you shouldn’t let politicians make policy outside the very narrow bounds set by the Constitution.
I’ve seen comments on YouTube videos from posters who are probably convinced that they are sensible, intelligent people saying idiotic things like “they should require NDT” (if they weren’t idiots, they’d take a few seconds to realize that NDT is not only required, but the Fireball in question passed all of them), or “all rides need more inspections/what do you ‘deregulation’ folks have to say now?” (they think inspections–so long as not made by government-employed slackers–are some kind of magic wand that will always find anything wrong, not realizing that the study of metal fatigue is not nearly as mature a science as they think it is). I’ve also seen articles decrying the lack of Federal regulation in amusement rides and calls to have rides of all types (even low-G rides for which high-tech testing would be an unfruitful, extravagant expense that would leave many small county fairs rideless) undergo extensive testing to operate.
The mainstream media also takes a slice of idiot cake, finding and reporting on “structural defects” that were identified and fixed years ago, and accidentally/on purpose not saying whether these issues were addressed on the one at the Ohio Fair. Implication by omission that the ride was operating with uncorrected, known defects. Although a few scattered outlets have responsibly found and reported the test results (not much harder to find than the service bulletins advising owners of the structural issues), far more newscasters have chosen to omit the ride’s clean bill of health in order to create a more sensational, let’s-make-big-government-bigger, rabble-rousing story.
So what’s the straight poop?
For anyone with the most basic understanding of the physics of mechanics and strength of materials, shutting down Freak Out because of what happened to Fireball is like banning oranges because you discovered a worm in an apple.
Freak Out and Fireball can both be described as groupings (six for Fireball, four for Freak Out) of four seats attached to a gondola that rotates at the end of a long arm that swings through around 240 degrees of arc. But there’s a significant difference in the nature of the gondola. In the Fireball, the sweep arms (which connect the seats to the swing arm) are essentially cantilever beams.
If you’re in building construction, you know what a cantilever is. If you’ve visited the Infinity Room of House on the Rock in Spring Green, you’ve stood on a cantilever. If neither of those gives you any perspective, think about trying to loosen a bolt. Fingers don’t work too well if the bolt is tight. So you get a wrench. If that doesn’t work, you get a longer wrench. You push down on one end of the wrench, and the other end exerts a moment (turning force) on the nut. The wrench is working like a cantilever. The sweep arms on the Fireball are like the wrench; the nut is the hub of the gondola, and the seats are your hand–tugging on the “wrench” with every swing. Observers watching the Fireball will tell you that in full swing, the sweep arms are visibly flexing with the strain of the G-forces every swing.
This stress can eventually fatigue the metal in the sweep arm, creating cracks that will eventually become breaks. The problem is that by the time these cracks are large enough to see with the naked eye–or even a loupe–the metal’s probably already broken. General inspections will not reveal them, no matter how competent the inspector.
The only way to detect these cracks before they become a threat to ride safety is with non-destructive testing, which–depending on what exactly is being tested–can include ultrasound, X-rays, magnetic particle testing, neutrons, and terahertz radiation, among other methods.
But the Freak Out is the same thing, isn’t it?
Uh, no. In the Freak Out, the sweep arms are not cantilevered. They actually attach at an angle–only about half of the distance from the fulcrum of the swing arm to the seats is actually the swing arm, the rest of the distance is sweep arms. When the arm is swinging, the sweep arms will want to pull in toward each other, a force that is resisted by spreader bars set between the arms. This puts much less stress (closer to the fulcrum=less force)–and therefore less chance of structural failure–on the sweep arms.
And one more difference between Fireball and Freak Out: The frames of both rides are part of a single trailer (the Fireball requires an “auxiliary” trailer for the other parts, the Freak Out does not), meaning there’s a rather substantial amount of structural steel on each end of the trailer. Fireball swings parallel to the trailer, so if a seat grouping falls off, it slams into that massive steel. Freak Out swings perpendicular to the trailer, so a loose seat grouping would be able to skid to a stop away from the ride (assuming there’s nothing massive near the ride), meaning the Freak Out is slightly less dangerous in the case that there actually is a seat detachment.
Is there anything an average fair-goer can do to tell if a machine like this is over-stressed?
Actually, you can snag a bit of a clue by watching how it’s operated. The greatest G-forces on either ride occurs at the bottom of the arc when the ride is in full swing. Spinning the gondola at this point puts even more stress on the sweep arms/seat attach points. A company operating for maximum thrill will spin the gondola throughout the ride. A company that wants their rides to last will only spin the gondola when the arc is small, or at the top of the arc when the ride is in full swing, and notably not rotating the gondola through the high-G point.