Safety
Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first laser as having a power of one "Gillette" as it could burn through one Gillette razor blade. Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight, when the beam from such a laser hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time.
Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is:
- Class I/1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players.
- Class II/2 is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to 1 mW power, for example laser pointers.
- Class IIIa/3R lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina.
- Class IIIb/3B can cause immediate eye damage upon exposure.
- Class IV/4 lasers can burn skin, and in some cases, even scattered light can cause eye and/or skin damage. Many industrial and scientific lasers are in this class.
The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength.
Certain infrared lasers with wavelengths beyond about 1.4 micrometres are often referred to as being "eye-safe". This is because the intrinsic molecular vibrations of water molecules very strongly absorb light in this part of the spectrum, and thus a laser beam at these wavelengths is attenuated so completely as it passes through the eye's cornea that no light remains to be focused by the lens onto the retina. The label "eye-safe" can be misleading, however, as it only applies to relatively low power continuous wave beams; any high power or Q-switched laser at these wavelengths can burn the cornea, causing severe eye damage.
Read more about this topic: Lazor
Famous quotes containing the word safety:
“Once women begin to question the inevitability of their subordination and to reject the conventions formerly associated with it, they can no longer retreat to the safety of those conventions. The woman who rejects the stereotype of feminine weakness and dependence can no longer find much comfort in the cliché that all men are beasts. She has no choice except to believe, on the contrary, that men are human beings, and she finds it hard to forgive them when they act like animals.”
—Christopher Lasch (b. 1932)
“Man gives every reason for his conduct save one, every excuse for his crimes save one, every plea for his safety save one; and that one is his cowardice.”
—George Bernard Shaw (1856–1950)
“He had a gentleman-like frankness in his behaviour, and as a great point of honour as a minister can have, especially a minister at the head of the treasury, where numberless sturdy and insatiable beggars of condition apply, who cannot all be gratified, nor all with safety be refused.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)