Eye safety is a prominent topic for any optics technology. Since FSO products, especially in urban areas, will be directing laser beams into potentially populated areas, laser eye safety is a fundamental design concern. Although the damage threshold for ultraviolet light is much lower than it is for infrared,  infrared light is still damaging to the eye. The upper limit to the intensity of the transmitted laser beam is a factor that most be closely correlated with urban area requirements. NASA supports the use of 1550nm versus Europe’s preferred of 1064nm, since 1064nm is closer to visible range and may damage vision.
Laser beams in the visible range emit light which passes through the eye and onto the retina. Wavelengths above 1400nm are absorbed by the eye’s cornea and lens and do not focus onto the retina. This allows a laser operating at 1550nm to output power about fifty times higher than visible since it is safer to view with the naked eye. This factor provides up to 17dB additional power strength, allowing the system to propagate farther, push through attenuation from atmospheric effects, and transmit at higher data rates. 
Paper: Wavelength Selection for Optical Wireless Communication Systems