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1.4.2 Thermal Injury
The most common cause of laser-induced tissue damage is thermal in nature, where the tissue proteins are denatured
due to the temperature rise following absorption of laser energy.
The thermal damage process (resulting in burns) is generally associated with lasers operating at exposure times greater
than 10 microseconds and in the wavelength region from the near ultraviolet to the far infrared. Tissue damage may also
be caused by thermally induced acoustic waves following exposures to sub-microsecond laser exposures.
1.4.3 Skin Injury
To the skin, UVA (315-400 nm) can cause hyperpigmentation and erythema (aka: sunburn). Exposure in the UVB (280-
315 nm) range is most injurious to skin. In addition to thermal injury caused by ultraviolet energy, there is also possibility
of radiation carcinogenesis from UVB. The shorter wavelengths are absorbed in the outer dead layers of the epidermis
(stratum corneum) and the longer wavelengths have an initial pigment-darkening effect followed by erythema if there is
exposure to excessive levels.
The hazards associated with skin exposure are of less importance than eye hazards; however, with the expanding use of
higher-power laser systems, particularly ultraviolet lasers, the unprotected skin of personnel may be exposed to extremely
hazardous levels of the beam power if used in an unenclosed system design.
Skin burns caused by lasers can happen quite fast and with great intensity. Protective clothing should be worn when
potential exposure to direct laser beams exist.
UVC: 200-280 nm exposure may cause erythema (sunburn), skin cancer, and burns.
UVB: 280-315 nm exposure may cause accelerated skin aging, increased skin pigmentation and burns.
UVA: 315-400 nm exposure may cause pigment darkening and skin burns.
Visible: 400-700 nm exposure may cause photosensitive reactions and skin burns.
Infrared 700-100,000 nm exposure may cause skin burns.
