Burn hazard of IR LED Array Question
Why is the radiant intensity of only one LED used for the burn hazard calculation and not the entire LED Array? Is there a scientific reason for this?

Yes. The lens of the eye focuses the image of each LED in the array to a different place on the retina. In other words, there is no point on the retina that is receiving light from more than one LED at a time.
Contrast this with the unfocused light falling on the cornea, each point of which does in fact get light from all of the LEDs.
The main danger to the retina with IR is that the iris of the eye does not react to bright IR sources. In an otherwise dark environment, the pupil remains wide open, allowing more of the IR to pass through the aperture.
According to Wikipedia, the human pupil can be as large as 9 mm. But the number you really want to use is the &quot;entrance pupil&quot; -- the apparent size of the pupil as viewed from outside the eye, which is larger because it is magnified by the cornea. I would use 10 mm, a number that telescope and binocular manufacturers use when designing eyepieces. This is 2x the area of 7 mm.