Containment and Restraint
How acceleration affects containment and restraint
Amusement rides thrill us by accelerating our bodies. Each curve, drop, loop, launch, or brake alters the rider's state of being, triggering inertial resistance -- the feeling that your body is headed in one direction while the ride is pulling you somewhere else. That's the "illusion of danger" that makes amusement rides exciting.
The ride's containment system includes the seat or frame you rest on; the supports, padding, belts and bars that hold you inside the vehicle; and bracing points that help you keep yourself from sliding as the ride accelerates.
The containment system on each ride is designed to support and restrain riders who fall within some limited range of sizes and shapes. Folks in the middle of that range will generally find the ride a safe, comfortable fit. For a standard full-sized ride, the mid-range is a 170-pound median man. For a kiddie ride, the mid-range will be signficantly smaller (there is no standard since kiddie rides may be targeted to different age groups within the kiddie market).
The farther you are from the median-sized person the ride was designed for, the higher the risk of a poor -- and possibly unsafe -- fit between you and the ride's containment/restraint system. This is one case where size really does matter.
Acceleration can help contain, or can work against containment
The direction of acceleration makes a difference in judging safe containment. Loose restraints alone won't endanger a rider, but ejection may be a possibility if the ride accelerates a rider toward gaps in the containment system.
- If the the ride only accelerates riders backward (i.e., the car moves forward) and the rider has solid support at his back, then there is no ejection risk for a properly-positioned rider -- even if the ride has no restraints at all. The ride's acceleration actually helps to keep riders safely contained.
- If the ride's forces push riders sideways (lateral acceleration), then the containment system should support riders and guard against slipping through the entry/exit gaps on the sides. Rides with bench seats that accommodate multiple riders should also employ some strategy to keep riders from sliding along the length of the seat. Lap belts, seat dividers, and "no single rider" policies that reduce the empty space on the bench are examples of common strategies to reduce sliding.
- If the ride accelerates riders' bodies forward (i.e., the car goes in reverse), or the ride climbs and dips (vertical acceleration), then the ride's containment system should restrain all riders -- including the smallest and largest -- well enough to keep them from being propelled out under/over the restraint.
Magnitude of acceleration matters as well. A major thrill ride requires more elaborate restraints than a kiddie coaster but, to be safe, the restraints on both must be designed to provide effective containment for all the riders allowed on board.
Patrons can help contain, or work against containment
Bracing - Ride designers employ bracing points on the floor and grab bars as part of the containment design to give riders more stability and reduce sliding. On rides without significant acceleration, bracing may be the only form of restraint provided. The instinct to brace against acceleration comes naturally, and often unconsciously. Most riders are unaware of how often they use this feature on amusement rides.
- Use the hand holds provided. They'll help to keep you from smacking into other riders or hard objects in the containment system. If you're smaller or heavier than average, bracing with your hands is even more important in helping you keep your seat.
- Parents should pay special attention to the position of bracing points when chosing rides for small children. If your child cannot reach the floor with his feet or cannot reach the hand holds, he may slide into an unsafe position.
Body Position - It's important to stay properly positioned for the entire duration of the ride. On seated rides, the designer has planned the experience to be safe for riders who keep their butt in the seat so their body makes a right angle at the hips and knees. If your child kneels on the seat or slides down into the footwell, he's no longer properly positioned. That means he may not be safely contained against the accelerations produced by the ride.
- If you add your own acceleration to the dynamic equation, by standing up on a coaster or rocking the tub of a Ferris wheel for example, you're putting yourself at risk for a serious fall and putting the riders around you in danger as well.
Clothing - The seating areas of amusement rides are generally made of low-friction material for easy cleanup. This also makes them slippery to ride on. Wearing low friction clothing, like nylon pants, magnifies the potential for slips -- especially for children and smaller adults who may not be secured as well by the restraints.
A special caution about momentary weightlessness
Humans are accustomed to using their muscles under the action of normal earth's gravity. If you tense your leg muscles to rise from a chair, for example, you automatically exert enough force to overcome 1g. That same level of muscle resistance will move you much farther if you're in an amusement ride that's created an effective acceleration of less than 1g.
Restraint design should account for this factor, by ensuring that sudden movements won't propel a rider out of the seat, but patrons should be aware of this effect. Help children understand the importance of sitting still, especially if the child has a tendency to shift, wiggle, or otherwise move around when seated. And never, never, never stand up in a an amusement ride to enhance the thrill. If you do it at the wrong moment, you could propel yourself right out of the car.
Choosing safe containment and restraint for kids
- To keep within limits (Merriam Webster)
- To close within bounds, limit or hold back from movement (WordNet)
When choosing amusement rides for children, it's important to look at the ride's containment system and the way it fits your child. You wouldn't put your preschooler in an adult-sized bike helmet because it won't protect her, and you wouldn't send her down the street by herself on a bike that's so big her legs can't reach the pedals. One glance is all it would take to realize that's a bad idea.
The same is true for the containment and restraint systems on some rides marketed for use by young children. Here are the key questions to ask before you put your child on any amusement ride:
- Does the containment system look like it will keep her "within limits"? Would it be difficult for your child to slip or move into an unsafe position? If so, then it meets the definition of "contain". If not, choose another ride for your child.
- If the ride has restraints, do they look like they'll keep her "close within bounds and limit or hold back her movement"? If so, then they really are restraints. If not, then they're something provided to restrain other people, bigger people maybe, but not your child. Choose another ride.
- Beware of dangling legs. If your child's feet don't reach the floor, she won't be able to brace herself against the ride accelerations. Never allow a child to ride alone if she can't brace herself. If you ride along with her, keep an arm around her and pay special attention to where her feet and hands wind up. Under-restrained children on dynamic amusement rides are like small carry-on bags in an airplane's overhead compartment -- they can shift during flight. Many ride designers believe it is your job, not theirs, to make sure every part of your child stays safely inside the car at all times.