Ask RideMan #3 - Emergency Stops

How do emergency stops and ride evacuations generally work? Why do they sometimes not evacuate a ride after there’s been a problem?

http://pointbuzz.com/content/ask-rideman-emergency-stops

Excellent article as always! I never knew emergency stops became that complex.

I know this does not answer the question of what would happen to all of the water on Thunder Canyon, but I saw this video a while back of a evacuation of a similar ride, the one from Bush Gardens Williamsburg more specifically. For those of you interested, here it is.

That was a very informative article. Thanks for writing and sharing. Its interesting to think about the instance of the cable that came lose on Skyhawk last year and how the ride was stopped.

First off, our Thunder Canyon (designed in-house, with a new control system recently) drains the entire trough when an E-stop is pressed. Depending on where the boats are in the course, they'll either come to a stop along the course or make it to the unload station or the area directly behind it. Ours shuts down entirely because if someone were to fall in the trough, we want to be able to stop the water flow immediately. Especially from the unload station because the pumps are only about 15-20 feet away from the station.

This is a topic that I actually end up think about a lot. And e-stops are things that that after working in rides (both as an operator and a trainer) I think could be much better designed. Granted, the park I work at has only one PLC controlled coaster and a few flat/water rides with actual PLCs so my perspective might be a little different. But personally I wish that Category 1 stops were more prevalent (and preferably with a separate, present Category 0 "Power Cutoff") because I don't like having to train that pressing the e-stop in certain situations can do more harm than good. Knowing many of the people that I've trained, I don't want them to have to not only decide that something's wrong, but also if it's safe to press the e-stop.

Ride's on fire? Cut off power: stop lifts/launches, shutoff/drain compressors, unlock magnetic gates, etc. Someone's about to be hit? (Category 1) E-Stop: closing brakes, stopping lifts/launches/drives, keeping gates closed/locked, continue monitoring sensors, etc. Especially since that could (theoretically) also mean restarting after whatever situation arose could be much faster, and less likely to need an evac.

You've got a lot of good points there, obviously rooted in experience. This is why we're seeing a lot of the electrical and controls standards re-written. An E-stop is the default response for a lot of bad things, but in the modern era of regenerative braking and other interesting complications, it's not always the *best* response.

Prior to 2014, ASTM F2291 actually specified three different stop categories, a Category 0, Category 1, and Category 2, with a Category 2 being a controlled stop with power left on to the actuators. In the re-write, there was actually a concerted attempt to eliminate any reference to stop categories and instead place the decision into the hands of the designer/engineer, so that the ride stop functions would be optimized for the requirements of the particular ride. That's the direction the industry is heading, and the first step in that direction is to rename the button: it's not an Emergency Stop anymore, but rather a Ride Emergency Stop. That's because some jurisdictional authorities still think an Emergency Stop needs to be a category-0 pull-the-plug electrical disconnect. Personally, I think those are two different things: the Ride Emergency Stop is the button you whack when you need the ride to STOP, RIGHT SHPXVAT NOW!, but if the ride is on fire or people are dropping from electrical shock, you need to pull an Electrical Disconnect or frob a shunt trip trigger. The idea is that if you have an electrical hazard, it makes sense to be able to dump the power no matter what that does to the ride. But if you want to make the ride stop, you need a button that actually makes the ride stop. That was the attitude of the ASTM subcommittee that did the control systems section re-write, and so I think we are going to see the ride designs actually push in that direction going forward.

--Dave Althoff, Jr.