Rami Arieli: "The Laser Adventure" Laser Safety Appendix, page 2

How are lasers classified?
National Safety Standards divide lasers into groups, according to radiation properties: wavelength, power output, pulse duration etc. These standards are adjusted every few years according to new knowledge about the interaction between laser radiation and biological tissue.

What are the risks of low power lasers?
The main damage that can be done by the low power, visible lasers is to the eye, and the following explanation will focus on it.

What is the difference between laser light, and "common" light?
The radiation emitted from the laser is electromagnetic radiation, and the distinctions between this "special" radiation and "common light" are:

Monochromaticity.
High power density (High Intensity per unit area), because of the small divergence angle of the beam out of the laser. Within laboratory distances, the laser beam is almost parallel.
Coherence - No special effect on the biological tissue is yet known because of coherence.