Lasers present an eye hazard if a person stares into the beam and resists the natural reaction to blink or turn away. Lasers with powers in excess of 500 mW may produce eye or skin damage from diffuse scattered light. Laser warning signs need to be posted for lasers with power in excess of 5 mW. A warning light should be activated when the laser is on.
Eye protection is required not only from direct impact of the direct beam, but also reflection (diffuse or concentrated) from surfaces. Goggles or safety glasses specifically designed for laser work are needed. They need to be fitted so that stray light cannot come in from oblique angles. The type of glasses needed depends on the laser type, wavelength, and optical density. Undesirable reflecting surfaces can be rough-finished and painted with flat charcoal black paint.
Direct laser impingement on the skin may cause considerable damage, especially where it is pigmented. A temporary injury to the skin may be painful and treated symptomatically. Injury to larger areas of the skin are far more serious as they may lead to serious loss of body fluids, toxemia, and systematic infections. Injuries to the skin can result either from thermal injury (temperature elevation in skin tissue) or from a photochemical effect (e.g. ``sunburn''). The warmth sensation resulting from absorption of radiation energy normally provides adequate warning for an avoidance reaction to prevent thermal injury of the skin from almost all sources except some high-powered, far infrared lasers.
Potentially toxic vapors which may result from laser-heating of materials need to be accounted for. Ozone is produced at times from flash lamps and high repetition rate lasers as the beam propagates through air. Ozone is extremely toxic. Proper ventilation is needed when vapors from liquid nitrogen coolants might otherwise starve the room of oxygen.