Tube trailers carry bulk liquids that are stacked in a rack type arrangement on the back of a truck trailer. This arrangement often is used to carry highly hazardous materials such as anhydrous hydrogen chloride. The tubes are manifolded together, but usually only one tube at a time is connected to a process for loading and unloading. Are "tube" trailers considered a single process?

If the "tube" trailers remain in transportation, the contents of the trailers are exempt from threshold determination. If the tubes no longer are in transportation, the entire grouping of tubes must generally be considered a single process, since they are co-located such that they could be involved in the same accident.