Glenn makes a very good point.
Those cheap green lasers leak IR to begin with, that's why I said to specify 5mW total output in your WTB thread, and if the crystals get completely knocked out, the laser can be producing A LOT of infrared and you would never even know it until the damage is done.
As a side note, if a green laser ever stops working DO NOT look into it. Put a small thin piece of paper on the laser, and turn off the lights, if you see a little reddish light on the paper it means the laser is still working but only producing unfocused infrared light.
If you are looking to mount something to a paintball gun, a red laser is a much better option, and the diodes are generally much tougher and more reliable. Cheapie reds are sold all over the place for very little.
I'm sorry to continue the kill joy parade, but there is no way to safely recreate the movie effect of the red beams without smoke... even 250mw+ red lasers don't really do much without smoke.