Thanks for asking this question. Resin safety is important and I’m happy to hear you want to make sure you are taking proper precautions.
The first thing I would recommend would be to review the SDS information of the resin you are using. That information will explain the precautions you need to take, including ventilation recommendations. Some resins also require the use of a respirator, although none that we sell have that requirement.
Taking the resins we sell as an example, an open window to allow air to move is generally enough. The idea is that you want the fumes to move away from you and where you are working. Two open windows to create a cross flow is even better. It gets a little tough during the winter when you can’t open a window. During those times, I like to have a fan close to me to circulate the air.
If you find the fumes bother you too much, or the resin you are using requires a respirator, make sure it is a NIOSH respirator approved for fumes and fits your face snugly. You only want air to come in through the cartridges on the front.
Now — here’s my experience. When I’m working with epoxy resins, I find that I can work indoors with them and circulate the air, either with open windows or a fan. I notice the smell, but find it’s no worse than fingernail polish. Polyester, however, is a different story. The smell drives me crazy! While it isn’t a requirement, I only work with it outside or with a respirator because it bothers me that bad. What I’m trying to say here is once you know what the manufacturer recommends, you can take it from there to adjust to your needs.