Can restraints ever unlock during ride?

Schwarzkopf76's avatar

Does anyone know definitively how the guy fell out of the drop tower at Paramount's (California's) Great America years ago? It would seem impossible to fall out of those things unless the harness came up.

Apparently they never found a definitive cause and did confirm that the restraint was locked. After this accident Intamin introduced seat belts as there was a suspicion that the child may have slid out underneath the bar.

Triple Tower at Hersheypark doesn’t have seatbelts and it scared the crap out of me. I wasn’t so concerned with “submarining” out under the OTSR but the thought of the harness popping open with nothing else to hold it just freaked me out.

But then again, what do I know?

With regard to the Giant Drop incident...

A diagram of the Intamin hydraulic restraint system can be found on PointBuzz.. That diagram describes the lap bars used on Top Thrill Dragster, but with minor mechanical differences the exact same system is used on the shoulder bars on the Giant Drop and other rides with similar restraints. Numbers in the next section correspond to the numbers on that diagram.

A failure mode has been identified in which, if the membrane in the accumulator (4) fails, thus allowing nitrogen into the hydraulic system, those nitrogen bubbles, in addition to permitting rod movement through their compressibility, can theoretically chatter through the check valve (2), holding the check valve open enough to allow unwanted reverse fluid movement and enabling the restraint to open unexpectedly. If this happens, the restraint would automatically re-lock once fluid motion forced the gas bubble out of the check valve (2), restoring normal function. Now, also in theory, with redundant locking cylinders, the odds of both cylinders having broken accumulators AND having the nitrogen bubbles hit the check valve at EXACTLY the same time seem astronomically small. I'd say probably less likely than the probability of Top Thrill Dragster getting a train exactly balanced on the top of the tower. But it has to be considered as a possibility.

Now, after the incident happened, I visited Six Flags Kentucky Kingdom and rode their Hellevator, the very first of the Giant Drop rides. Six Flags had hastily tied safety belts to the shoulder bars and let the ride continue to operate. I sat in the seat, pulled the shoulder bar down until it touched my shoulders, then experimentally slid my hips forward in the seat and dropped my legs. I realized that by sliding forward far enough to drop my thighs into a nearly vertical position, there was nearly enough space that I could easily slide out of the seat. I slid back in the seat, fastened the safety belt, and enjoyed the ride, making no further adjustments to the shoulder bar. I also noticed that when the car hits the brakes, the rider feels a downward force of about +3Gz. A rider who was in the vertical position I had assumed for my little experiment would likely feel sucked right out of the ride.

I concluded at that point that shoulder bars are not an effective restraint on the Giant Drop as they do not do what is required of a restraint on that ride, namely to hold the rider *back* in the seat; in fact the shoulder bar may actually be contraindicated on the ride as an effort to make the restraint tighter will force the rider to slouch in the seat, actually forcing the hips forward into a dangerous position. This is why I no longer ride the drop ride at Kings Island: getting the bar down far enough to fasten the safety belt requires exactly this from me.

Incidentally, S&S has abandoned the hydraulic locking restraints. Their new seat and restraint design (found on the Hersheypark towers) uses a redundant all-mechanical system with a toothed locking rod.

--Dave Althoff, Jr.

Last edited by RideMan,

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Jeff's avatar

Intamin's history seems to demonstrate a failure in understanding human factors before mechanical systems. What you describe is similar to the early hyper trains, and the change that came by the time Dragster opened. You don't need those dumb leg guards, you just need the seat to be deep enough that the lap bar touches your thighs, not your gut, and your butt it's lower than your knees.

Jeff - Editor - - My Blog - Phrazy

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