last twenty years, the kinds of equipment to be found in playgrounds has changed, often towards safer equipment built with plastic. For example, an older jungle gym might be constructed entirely from steel bars, while newer ones tend to have a minimal steel framework while providing a web of nylon ropes for children to climb on. Playgrounds with equipment that children may fall off often use rubber mulch on the ground to help cushion the impact. Playgrounds are also made differently for different age groups. Often schools have a playground that is taller and more advanced for older schoolchildren and a lower playground with less risk of falling for younger children. Safety discussions do not normally include an evaluation of the unintended consequences of injury prevention, such as older children who do not exercise at the playground because the playground is too boring. Safety efforts sometimes paradoxically increase the likelihood and severity of injuries because of how people choose to use playground equipment. For example, older children may choose to climb on the outside of a "safe" but boring play structure, rather than using it the way the designers intended. Similarly, rather than letting young children play on playground slides by themselves, some injury-averse parents seat the children on the adult's lap and go down the slide together. This seems safer at first glance, but if the child's shoe catches on the edge of the slide, this arrangement frequently results in the child's leg being broken. If the child had been permitted to use the slide independently, then this injury would not happen, because when the shoe caught, the child would have stopped sliding rather than being propelled down the slide by the adult's weight. Also concerning the safety of playgrounds is the material in which they are built. Wooden playgrounds act as a more natural environment for the children to play but can cause even more minor injuries. Slivers are the main concern when building with wood material. Wet weather is also a threat to children playing on wooden structures. Most woods are treated and do not wear terribly fast, but with enough rain, wooden playgrounds can become slippery and dangerous for children to be on. Regulation In the United States, the Consumer Product Safety Commission and the American National Standards Institute have created a Standardized Document and Training System for certification of Playground Safety Inspectors. These regulations are