When lasers are classified as Class I, II, IIIa etc. is that based on the maximum power output in the case of a failure, or is it based on the expected operational power output?
Lasers are classified by their potential for causing biological damage.
Laser classifications are as follows:
Class I - These lasers cannot emit laser radiation at known hazard levels.
Class I.A. - This is a special designation that applies only to lasers that are “not intended for viewing,” such as a supermarket laser scanner. The upper power limit of Class I.A. is 4.0 mW.
Class II - These are low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
Class IIIA - These are intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class.
Class IIIB - These are moderate-power lasers.
Class IV - These are high-power lasers (cw: 500 mW, pulsed: 10 J/cm2 or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.
(As listed on this How Stuff Works page)
Right. But are those classification based on the normal output power, or the output power if the device fails “hot”?
I’m guessing it deals with normal operations but I’d like something better than my opinion.
Pretty sure it’s normal operation. When a laser fails, it doesn’t go out of control and suddenly emit some gigundud burst of super-laser power. The natutral response of a laser to something going wrong is to simply stop working. Having worked with a lot of lasers over the past 30 years, this is certainly my experience.
Lasers are the high-tech equivalent of those strings of little Christmas lights that go out altogether when one bulb fails. Only with a laser, what went wrong is not as obvious as one of the bulbs failing.
Class MDCDXXII–1920’s Style Death Rays. 
I thought that was class MCMXX
Silly jrfranchi!
Everybody who is anybody on the SDMB knows that the first true 1920’s Style Death Ray was made by the great Hans Zarkov.
In the link below, Professor Zarkov is pictured with his first Death Ray.
http://flashgordon.ws/images/zar032.jpg
Visible is the THX 1138 4EB Generator Coil of the weapon.
Well, I’m thinking of a poorly designed one where you wind up shorting through the semiconductor. Yeah it’ll fail, but I’d imagine the output will peak before quickly decaying away.
But I’ll go with normal operations. It’d be too hard to classify them based on just one of a multitude of failure modes.