System Environment

Hey guys,
was wondering if you could help me with something. I'm an apprentice and at work the boss wants me to do a write up about 'the PLC and Systems Environment'. Basically meaning that i have to do a load of research on what sort of environment a PLC has to be in. If there is a god and any of you can help me by directing me to a couple of web sites i would be forever greatful!

XX Acid XX

Any PLC manufacturer

http://www.ab.com

http://www.sea.siemens.com

http://wwww.gefanuc.com

http://www.automationdirect.com

There are more but that should tell you alot, look at technical, specifcations or data sheets. Most are constructed for harsh environment but there are some that are made for some of the harshest environments...outdoors, cold weather, extreme heat, hazardous areas, etc etc.