When I was on Prozac and Klonopin I could work part time, but had to be careful of chemicals (new furniture, building products, glues, molds, remodeling, perfumes, basements) or things (pets) at work, that would set me off. I believe working from home is the best answer, but I loved the social interaction. I had to quit many, many jobs on the spot, due to them changing something in the environment at work, where I would start reacting with the change, even when I was doing better on Prozac and Klonopin. I do not think any field is safe, because employer's can change the environment where someone might react to a change. Since Prozac and Klonopin stopped working 3 years ago, I would not be able to work, even from home.
I do not believe many fields are good for people with MCS. Any field with chemicals or smells would set them off. Even offices are unsafe, as they remodel often.
I met many people with MCS in Dallas, who were not as severe, and I believe they could have worked in a "safe" job. I do not know the percentage because I did not know everything about the people that I met. I have no idea how many people with MCS could work. It depends on how severe you are. Some people only have sensitivities to a few chemicals. People that have sensitivities to all chemicals could not work outside the house. MCS is extremely limiting and life changing.