There are several things that are different about laser cutting styrene as opposed to many other materials. Is it safe to laser cut styrene? Safe, yes, but it is a little tricky.  Styrene tends to cut with rolled edges so the thinner the better for clean cuts. You can do better with less power, more speed, and two passes. Another option for straight cuts is to have the laser score it then break out the pieces. What about issues with poisonous fumes? Styrene doesn't contain PVC, so no worries there with fumes. As long as your laser has a full filter system that extracts outdoors, it should not be an issue. However, cutting anything that has chlorine in it like PVC generates chlorine gas, which despite your filtration system, might affect your lungs. The thing with cutting PVC or other plastics with chlorine is that not only is it bad for your lungs, but it is bad for your equipment. It can deteriorate your optics, corrode the metal, and otherwise foul your electronics.