Roll-over protection structures and falling object protection structures have been standard safety equipment for over 20 years. They are required by OHSA-type laws in the U.S. and other countries. Today they must also protect from foreign object penetration (jill-pokes), as well as roll-overs and falling objects. Some machines, such as as Tree harvesters, now are fully enclosed with glass or plexiglass and steel framework, allowing the operator to enjoy air conditioning and stereo music. An example of a ROPS is shown below on a Timberjack skidder.