Well, I don't know the legal or Health&Safety aspects.
They quite rightly tend to err on the side of safety and worst-case situations.
But we could discuss this here til the cows come home.
Maybe its time for you to do some technical research?
I find it all a bit strange. No-one seems to mind being flashed at by the lasers at a Supermarket checkout.
But fire some wimpy modulated IR beam at someone's big toe for 0.1 seconds and aaargh you've blinded me.
I get confused between sensible/valid safety concerns and Real World practicality.
I wouldn't worry at all if you aimed a baby I/R laser at me from 20 feet and pressed the button for a tenth of a second.
The chance of you getting me in the eye are tiny and the chance of any damage occurring even less.
Its all about energy/time/area after all.
And I think you can get optical plastic filters which attenuate near IR, so maybe there are IR laser goggles?
Or you could limit rate-of-fire or modulation or divergance to a 'sensible' level.
As for the "How do you tell..." - what a tricky one.
Why not just copy (and improve upon?) what the Big Boys do?
But a nice project nonetheless - and I wish I was doing it
PS. I haven't read in detail that data sheet on that LED.
BUT, from experience using OD-100 and OD-880 IR LEDs you will have to pay careful attention to pulse length and duty when you start cranking up the Amps - otherwise poof or serious degradation in O/P.
I was using a lensed system with the above LED + Ph/Diode for people detection.