Any equipment that is used with pure oxygen or an oxygen level above ____ must be cleaned for oxygen service.

Equipment that is intended for use with pure oxygen or oxygen levels above 40% must be cleaned for oxygen service to prevent the risk of fire or explosion. At this concentration, oxygen becomes highly reactive, increasing the likelihood of combustion when in contact with oils, greases, or contaminants that may be present on the equipment surfaces.

Cleaning for oxygen service involves removing all potential contaminants and ensuring that surfaces are free from any materials that could ignite or combust in high-pressure oxygen environments. This diligence significantly reduces the risks associated with working in environments where elevated oxygen levels are present and is a critical safety measure in dive operations and other applications involving enriched oxygen mixtures. Thus, the correct threshold for requiring equipment to be cleaned for safe use in high oxygen environments is indeed 40%.