Safety class

Simplified description

Class 1 Laser Inherently Safe   Visible/non visible

The accessible laser radiation is not dangerous under reasonable conditions of use. Limited to 0.39 mW

Class 1M   Safe without viewing aids 300-4000nm

The accessible laser radiation is not hazardous, provided that no optical instruments are used. Limited to 0.5 W.

Class 2 Low Power Visible only

The accessible laser radiation is limited to the visible spectral range (400–700 nm) and to 1 mW accessible power. Due to the blink reflex, it is not dangerous for the eye in the case of limited exposure (up to 0.25 s). 
Example: some (but not all) laser pointers.

Class 2M   Safe without viewing aids   Visible only

Same as class 2, but with the additional restriction that no optical instruments may be used. The power may be up to 0.5W, but the beam diameter in accessible areas is large enough to limit the intensity to levels which are safe for short-time exposure.

Class 3R   Low/medium power   Visible / non-visible

The accessible radiation may be dangerous for the eye, but can have at most 5 times the permissible optical power of class 2 (for visible radiation) or class 1 (for other wavelengths). Limited to 5 mW.

Class 3B   Medium / high power Visible / non-visible

The accessible radiation may be dangerous for the eye, and under special conditions also for the skin. Diffuse radiation (as e.g. scattered from the some diffuse target) should normally be harmless. Up to 0.5 W is permitted in the visible spectral region. 

Class 4   High power Visible / non-visible

The accessible radiation is very dangerous for the eye and for the skin. Even light from diffuse reflections may be hazardous for the eye. The radiation may cause fire or explosions. Laser radiation ->0.5 W.