This question was discussed quite often here on DB, so I'd recommend going through the archive - you will see different opinions there. Myself, I remember posting about it in the last time in the following threads, but I am sure there are many more comments to the topic in the archive:
http://forums.deeperblue.net/beginne...co2#post634184
http://forums.deeperblue.net/safety/...les#post632866