You shouldn't be breathing the fumes off of anything that you are welding. It's not always possible, but anytime that you can rig up something so you won't be breathing the fumes the better. If you do a lot of welding in your garage or wherever, then spend a little money and rig up a vacuum tube that will draw the fumes in.
The only reason I say this is for one, my dad ended up with COPD and emphysema. The other reason, and I really don't know anything about it but it is called "Pick's Disease". From what has been told to me from my neighbors wife. According to her, the doctors told her that all of the years of welding that her husband did, contributed to the disease. Her husband was a welder where I worked. Most welding was done in a closed room of maybe 12'x12', but had ventilation tubes to draw the fumes out.
As far as the Pick's Disease, Dave (his name) started out with small memory lapse. It amounted to about the same thing as everyone experiences from time to time. Forgetting someone's name, forgetting what you were talking about, and so on. It progressed into him forgetting what he was doing, and progressed to the point that he had a hard time with speech, then with a hard time communicating what he was trying to convey as far as instructions. In a few months time, he progressed to the point that he could no longer work. I would be in the garage and he would show up out of nowhere. On day, we come in from working out in the front yard, walked into the house and there stood Dave in our kitchen. Another time we were sitting watching TV and Dave walked in to our family room. Each and every time, we had to call his wife and she would leave work to come and get him.
One day we heard his a call come across the scanner of a man walking down the road with a rifle. The cops went to investigate and it was Dave. He walked into the Fairgrounds to the Flea Market that weekend, bought a BB gun and was walking home with it. When the cops pulled up and told him to drop it, he raised the gun. Not being able to communicate, the cops pulled their guns. Luckily, one of the officers pulled up and knew Dave from Church. It could have been ugly.
As the disease progressed, it was really sad. This man that used to be a Pastor had been reduced to the mentality of a 1 year old. He would show up in my garage, he would be drooling, there were times that he showed up and he had **** himself. Numerous times he would leave the house at night and be walking down the road totally ****. His wife finally had to put him into a care facility. It wasn't too long after that, that he passed away.
Like I said, I don't know about whether the welding fumes caused it or not, other than what I was told by his wife. Also after he passed away, they did change things around the shop so any welding was not in a confined area. You can take it for what it is, but if it were me, and the older I get, the more conscientious I am about chemicals, whether breathing fumes, or by body contact. I keep latex gloves in the garage, I have 3M respirators, I have shop safety glasses everywhere and just basically take a lot of precautions way more than I used to.
Here are a few site from a quick search explaining some of the hazards of welding and fumes.
http://www.toxicweldingrodfumes.com/
http://www.welding-rod-dangers.com/exposure/exposure.htm
http://www.cdc.gov/niosh/pel88/welding.html
http://www.everlastgenerators.com/welding-diseases-and-hazards.php
http://www.asse.org/practicespecialties/articles/weldingfumes.php
