Friday, January 31, 2014

PSA: Laser Safety

Let's get down to business. First you get the PSA, then you get the story and the why.

Lasers can be outright dangerous (especially incident light). If you are going to use a laser be sure to take appropriate safety precautions. This means protect your eyes (and prevent fires)...

Note: this PSA applies to any laser with a power output greater than 5 mW.

To do this first figure out the wavelength of the laser. It should be listed on the laser's spec sheet. Based on the laser's wavelength purchase a pair of safety glasses (these cover multiple wavelengths, but do your own research). Anytime that the laser is on wear the glasses. Simple. Another option is to keep the laser system in a completely opaque enclosure, but this will obviously prevent viewing of the assembly during use. To prevent fire, simple keep the laser from dumping too much power into a single spot for too long a time.

Now it is story time. A perfect storm of events has prompted this PSA including but not limited to:

  • "Playing" with outright dangerous lasers in the development of my own 3D printer design
  • Musing about my personal design philosophy
  • Realizing and articulating that SAFETY is my absolute number one design priority (for myself, my colleagues, my potential customers, and the public at large)
  • Reading about the apparent flood of low cost laser machines on the market

As you may have noticed, there seems to be a new Reprap style laser machine hitting the web everyday. There is a successful Kickstarter for the 100 mW MicroSlice, there is the 1 W LaserV on OpenBuilds, and there is even a 1.7 W hombrew 3D printer/laser combo on r/reprap. All of these designs have two highly disturbing features in common: high power lasers and open air frames.

Let's take a look at the actual danger associated with lasers and incident light.There is an excellent Wikipedia page on laser safety. I highly recommend reading this page as a primer. About 1/3 of the way down the page there is a highly telling chart that I have conveniently pasted below. The graph displays maximum permissible exposure in Watts per unit area vs exposure time for various wavelengths. What this means is that if your eyes are exposed to the power levels shown for the indicated time, you will get permanent eye damage.

Let's run through a real life example. We ca use the absorption curve for Ethidium-bromide-ABS to drive the example. Below 300 nm (ultraviolet) this material absorbs most laser radiation, converting it to heat energy. However in the visible spectrum, the laser reflects most of the laser radiation. If we were to shine a 1.7 W blue laser (355 nm) at this material most of the energy would be reflected. If a portion the size of your iris landed on your iris, you would have permanent eye damage in less than a second.

The moral of the story is please, please, please be safe when using lasers. Always wear appropriately rated safety glasses or ensure that your laser is fully enclosed (I prefer both).