I was hoping someone would say this. What creationists actually mean by "observational science" is that observations are only valid when an event is witnessed first hand. Observations of the evidence left behind after an event are not accepted as valid.
By this creationist definition of "observational science," if you observed someone shoot someone else, that's a valid observation.
But if all you did was make observations of powder burns, fingerprints and rifling marks for analysis, those are not valid observations.
You know, this begs the question: if observational science, as creationists allude to, requires direct observation of the event in order to classify it as fact, than how precisely can they claim with all certainty that Genesis and The Flood happened as absolute facts if they were not there to see it?