Class 2 (or class II in the old classification system) lasers should be used whenever possible. The output of these lasers is limited to 1 mW, which is sufficient for many purposes (such as alignment), but they are considered safe due to the blink reflex, which limits exposure to about 0.25 s. Users of class 2 lasers should be aware, however, that intentional suppression of the blink reflex can lead to eye injury. Users should not stare into the beam. Alignment lasers may be required for alignment of an x-ray flightpath at CHESS, which is generally at about eye level; in such cases, special care should be taken to prevent exposure to unaware persons outside of the hutch.
Although lasers producing 5 mW output (class 3R, or class IIIa in the old classification system) are commonly marketed as hand-held laser pointers in the United States, they are only considered safe when handled carefully and with restricted beam viewing. These lasers should only be used when class 2 lasers are inadequate. Due to the fact that these lasers are generally mounted in a fixed position, possibly at eye level, the risk of injury is much greater than with a hand-held laser. Use of class 3R and IIIa lasers in a fixed position
should be treated as hazardous. A standard operating procedure will not be required, but the Laser Safety Officer (LSO) or his/her delegate should approve their installation. The laser output must be contained within a well-defined nominal hazard zone (NHZ), for example, an x-ray hutch or other room, and a sign must be posted outside the NHZ indicating the nature of the hazard. It will not be necessary to enclose the NHZ with a laser safety curtain for a class 3R or class IIIa laser, but it is the users responsibility to restrict laser radiation exposure to within the NHZ.
Class 3B (IIIb) and class 4 (IV) lasers present significant hazards, and require special operating procedures and LSO approval before use.
Lasers that are not labeled with a classification or output power cannot be used without approval from the LSO.