How to assign duty class (S1 -….S9) of electrical motor.

Is there any standard reference to assign duty class of motor.? Generally it has to be given by end user and this is of more academic interest for a mechanical engineer rather than a problem. For example, if I have to replace a motor of air compressor, refer compressor manual and motor data-sheet or for that matter old motor tag plate and order new motor. Another example for EOT crane, typically get reference from crane classification/duty class which is also corresponds to motor duty class in the similar manner or may be it is well known in industry that it is CDF 40% or 25 % motor. Question is without taking any reference, is there any correct theoretical method or standard which classify duty class of motor.