The high powered lasers that are increasingly used in laser shows can produce enough light radiation to cause permanent eye damage as well as severe skin burns. Should any accidental direct exposure occur, there is a high chance of injury to the individual.
The lens and cornea of the eye concentrate light and focus it on the retina. In a sense, the eye acts like a magnifying lens to concentrate the light. The retina translates the light into nerve impulses that travel through the optic nerve to the brain, where an image is perceived. If a laser beam enters the pupil of the eye, its power is concentrated by the lens into a smaller area, resulting in more light and heat per unit area. The intensity of the laser beam can actually be increased by 10,000 times or more by the time it reaches the retina! If the laser beam strikes the eye from the side (hitting the area of the eye used for peripheral vision), damage can occur but may not be noticed right away, although a number of burns in this part of the retina might impair vision. If the beam comes directly head on at the eye (striking the eye's area for sharp vision) the burn could result in a very noticeable blind spot or other serious impairments to vision. It may only take a fraction of a second for the damage to occur.
Because the eye focuses light, it is the most sensitive part of the body to laser radiation. But severe skin burns can also be caused by laser light. With some lasers, you can light a cigarette merely by putting the end of it in the laser beam. If the beam has enough power to light a cigarette, you can imagine the kind of skin burns it could cause.
The question of safety or hazard with laser light shows is "To what levels of power might people be exposed?" The mere presence of a high powered laser does not necessarily pose a hazard. Scanning safeguards and other means can be taken to protect people from laser hazards. But:
There is a hazard whenever a high power laser beam could possibly strike someone, particularly in the eyes.
The beam could be dangerous even if it is reflected off a smooth or shiny surface. If the laser is high enough in power, it could be dangerous even when the beam is reflected off a rough surface or scattered by fog or smoke.
It only takes a fraction of a second to cause serious injury!
These are the reasons for the government's safety requirements for laser light shows. But such efforts cannot ensure absolute safety. So it is important that you, as a person involved with producing a laser show, carry out your part in laser safety.
Source: Excerpted from Laser Light Show Safety: Who's Responsible? PDF June 1980; Revised May 1986