operators must comply with limitations
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Indeed CJ, the operators must comply with the limitations specified by the manufacturers.
If there is an need to vary, clarify, adjust or disambiguate those limitations then the new acceptable limits must come from the manufacturer
There's a difference between limitations and recommendations. I don't believe that any manufacturer has published limitations relative to what you must not ingest. They may however published limitations on things like EGT and RPM and part removal times