Lasers are divided into safety classifications in the US by the American National Standard Institute (ANSI) and globally by the International Electrotechnical Commission (IEC). The classifications below from the revised system (2002) apply to non-magnified laser devices.
Safe under all conditions of normal use.
Applies to only visible light lasers (400-700nm). These devices are considered eye-safe because the blink reflex will limit exposure to less than 0.25 seconds. Intentional suppression of the blink reflex could lead to eye injury. Most laser pointers are class 2 devices.
3R lasers in the visible spectrum have continuous wave (cw) emission 5mW or less. These devices are considered safe if handled carefully with restricted beam viewing.
3B lasers are hazardous to the eye when viewed directly. For visible and infrared devices emission power is limited to 0.5W. Protective eyewear, key switch and safety interlock are required safety features.
Class 4 lasers include all lasers that emit power in excess of 3B limitations. Eye protection is needed to limit both direct and diffuse reflected exposure. Key switch and safety interlocks are also required safety features. Most scientific, industrial, military and medical lasers fall into this category.