Lasers are classified into four broad areas depending on the potential for causing biological damage. When you see a laser, it should be labeled with one of these four class designations:

• Class I - These lasers cannot emit laser radiation at known hazard levels.
• Class I.A. - This is a special designation that applies only to lasers that are "not intended for viewing," such as a supermarket laser scanner. The upper power limit of Class I.A. is 4.0 mW.
• Class II - These are low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
• Class IIIA - These are intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class.
• Class IIIB - These are moderate-power lasers.
• Class IV - These are high-power lasers (cw: 500 mW, pulsed: 10 J/cm² or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.