skin or eye within the nominal hazard zone. (The nominal hazard zone is the area around a laser in which the applicable MPE is exceeded.) Many industrial, scientific, military and medical lasers are in this category. Safety measures General precautions Many scientists involved with lasers agree on the following guidelines: Everyone who uses a laser should be aware of the risks. This awareness is not just a matter of time spent with lasers; to the contrary, long-term dealing with invisible risks (such as from infrared laser beams) tends to reduce risk awareness, rather than to sharpen it, primarily due to complacency. Optical experiments should be carried out on an optical table with all laser beams travelling in the horizontal plane only, and all beams should be stopped at the edges of the table. Users should never put their eyes at the level of the horizontal plane where the beams are, in case of reflected beams that leave the table. Watches, and other jewelry that might enter the optical plane, should not be allowed in the laboratory. All non-optical objects that are close to the optical plane should have a matte finish in order to prevent specular reflections. Adequate eye protection should always be required for everyone in the room if there is a significant risk for eye injury. High-intensity beams that can cause fire or skin damage (mainly from class 4 and ultraviolet lasers) and that are not frequently modified should be guided through opaque tubes. Alignment of beams and optical components should be performed at a reduced beam power whenever possible. Protective eyewear The use of eye protection when operating lasers of classes 3B and 4 in a manner that may result in eye exposure above the MPE is required in the workplace by the US Occupational Safety and Health Administration. Protective eyewear in the form of appropriately filtering optics can protect the eyes from the reflected or scattered laser light with a hazardous beam power, as well as from direct exposure to a laser beam. Eyewear must be selected for the specific type of laser, to block or attenuate in the appropriate wavelength range. For example, eyewear absorbing 532 nm typically has an orange appearance (although one should never rely solely on the lens color when selecting laser eye protection), transmitting wavelengths larger than 550 nm. Such eyewear would be useless as protection against a laser emitting at