IR LED - Help me convert 'Maximum radiant power' to irradiance (Watts per meter squared)
W/sr is the density of light coming out of the LED, in photons-per-solid-angle.  To convert that to irradiance, you need to know how far away the illuminated item is because the light is spreading out according to the inverse-square law.

1 steradian has a surface area of 1m^2 at a range of 1m, 4m^2 at 2m, 100m^2 at 10m, 0.01m^2 at 0.1m, etc.  So assuming there are no additional optics, the irradiance at distance D metres will be 3/D^2 W/m^2 for your 3W/sr source.

To take a step back though, you get roughly 1.5kW/m^2 irradiance from the sun.  To reach that intensity from this LED you'd have to be within 5mm of it, i.e. your greatest hazard is probably poking yourself in the eye.  If it were a UV LED, the answer would differ, but this is IR and therefore very much non-ionising.