The use of gas ratios to indicate a single possible fault type is an empirical process based upon the
experience of each individual investigator in correlating the gas analyses of many units with the fault type
subsequently assigned as the cause for disturbance or failure when the unit was examined. This process was
attributed to Doernenburg and subsequently confirmed by Rogers on European systems, from which the
bulk of the diagnostic correlation is obtained. U.S. investigators have applied the European rules to units on
U.S. systems with varying degrees of success; however, a U.S. database of comparable size to the European
reports does not exist.