The hazardous range of laser beams and their reflections from surfaces must be known when one uses lasers outdoors in areas where individuals could be exposed above the applicable exposure limits. In this paper, we describe formulas that can be used to calculate these hazardous ranges, and a few experimental data are presented that indicate the validity of the formulas and the underlying assumptions. The hazardous range depends on the laser parameters, the exposure limit, the atmospheric attenuation, the distance between the laser and reflector, the dimensions of the reflector, the angle of incidence on the reflector, and the surface parameters such as the reflection coefficient and flatness of the surface. The hazardous range of some commonly used lasers by the U.S. Army extends from 5 to 25 km for unaided viewing.
Willem P. Van De Merwe and Wesley J. Marshall, "Hazardous ranges of laser beams and their reflections from targets," Appl. Opt. 25, 605-611 (1986)