What are the quantifiable criteria that are used to assign a safety classification to a laser? Googling finds me only vague subjective descriptions, like "safe to use under normal conditions" or "capable of harm". Presumably, whoever assigns these labels isn't simply shining them into someone's eyes to see if it "does harm".
I see lasers for sale online that often don't advertise their classification, but give all other details about the laser. For example, if one was advertised as 0.25mW output at 800nm wavelength with a 75% duty cycle, how would I estimate it's safety classification?