Re: Inspection Humidity control
I don't know of a standard (certainly not ISO) that specifies a humidity range, because needs vary among the materials being examined and the equipment used to inspect them with.
I am more familiar with discussions like this one,
Temperature and Humidity requirements for a Calibration Laboratory. Limits are set for calibration labs to ensure a minimum of variation that impacts equipment responsiveness and performance in reading dimensions, weight, volume etc.
See also some links to related threads at the bottom of the page.