<P> ROPS are commonly fitted to 4x4's, pickup trucks, earth moving equipment, soil compactors and utes used in the mining industry . Products such as this were developed out of necessity so employees travelling around or within mine sites were provided with extra protection in the event of a fleet vehicle roll over . </P> <P> In the US, ROPS designs have to be certified by a Professional Engineer, who will normally require a destructive test . The structure will be tested at a reduced temperature (where the metal is more brittle), or fabricated from materials that have satisfactory low temperature performance . </P> <P> In Australia and most other countries, the International Organization for Standardization has guidelines for destructively testing ROPS structures on earthmoving machinery, excavators, forestry equipment and tractors . Theoretical performance analysis of major new design ROPS is not permitted as an alternative to physical testing . </P> <P> Some tractor operators have raised concerns about using ROPS in low - clearance environments, such as in orchards and buildings . In response, NIOSH developed an Automatically Deploying Rollover Protective Structure (AutoROPS) which stays in a lowered position until a rollover condition is determined, at which time it deploys to a fully extended and locked position . It is currently working with manufacturers to streamline the commercialization of this technology . The Division of Safety Research branch of NIOSH has developed cost - effective rollover protection structures (CROPS) for four tractor models (Ford 8N, Ford 3000, Ford 4000, Massey Ferguson 135), in an effort to provide safety for older model tractors . </P>

What is the difference in terms of who is enclosed in protective cages or structures