In article ,
Roger wrote:

I've worked with HeNe tubes before. The ones I've seen are a foot to 1.5
feet in length; they are usually 1 milli-watt to 5 milli-watts laser output
power. You would not want to get the beam directly in your eye, it could
cause some damage. I have heard that the eye very quickly turns to avoid
being damaged though. The little laser pointer that you can buy all over
that work off of watch batterys are in the same range of power. A HeNe tube
puts out a much better quality of laser light and more coherent than a
little laser pointer and it will be most likely red light. You won't see
the beam at these low power levels, just a intense bright spot on what ever
you aim it at. Note that the brightness of the spot is much brighter that
our eyes can determine. If it is low power like I'm guessing, I don't think
you need the key switch; just replace it with a toggle switch, I think US
and Canada changed the rules on low power laser otherwise you wouldn't be
able to by a laser pointer toy.

The ML855 seems to be rated as a 5 mW laser.

According to the Great Font of Trackless Factoids (i.e. Wikipedia)
this is right at the upper limit of Class 3R ("considered safe if
handled carefully, with restricted beam viewing"). It's well above
the 1 mW limit for Class 2 lasers ("safe because the blink reflex will
limit the exposure to more than 0.25 seconds") which is usually the
category in which you find inexpensive laser pointers, I believe.

Anything above 5 mW is at least Class 3B, which does require a key
switch and a safety interlock.

So, replacing the keyswitch with a new one, rather than with a toggle,
would be prudent. Otherwise, the laser might someday end up being
toggled on by someone who thought it was no brighter (or more
hazardous) than a $2 laser pointer, and careless use might result in
someone's eye being damaged.