Fuel oil and related equipment which were often designed for lighter fuels. For comparison, BS 2869 Class G heavy fuel oil behaves in similar fashion, requiring storage at , pumping at around and finalising for burning at around . Most of the facilities which historically burned No. 6 or other residual oils were industrial plants and similar facilities constructed in the early or mid 20th century, or which had switched from coal to oil fuel during the same time period. In either case, residual oil was seen as a good prospect because it was cheap and readily available. Most of these facilities
Interlanguage fossilization opinion. The term, borrowed from the field of paleontology, conjures up an image of dinosaurs being enclosed in residue and becoming a set of hardened remains encased in sediment. The metaphor, as used in SLA literature, is appropriate because it refers to earlier language forms that become encased in a learner's interlanguage and that, theoretically, cannot be changed by special attention or practice of the target language. Despite debate over the degree of permanence, fossilization is generally accepted as a fact of life in the process of SLA. Many researchers have attempted to explain this. Workers have attempted to discover: