> Although the fumes from epoxy are not objectionable, it makes sense to limit your exposure because of the risk of sensitization reactions. See General Safety Guidelines from West System. The following is from that document: Avoid breathing concentrated vapors and sanding dust. WEST SYSTEM epoxies have low VOC, but vapors can build up in unvented spaces. Use fans or other means to provide ventilation when working with epoxy in confined spaces, such as boat interiors. When adequate ventilation is not possible, wear a NIOSH (National Institute for Occupational Safety and Health) approved respirator with an organic vapor cartridge (NIOSH Approval #TC-23C). Provide ventilation and wear a dust mask when sanding epoxy, especially uncured epoxy. Breathing uncured epoxy dust increases your risk of sensitization. Although epoxy cures quickly to a sandable solid may take over two weeks at room temperature or post-curing to cure completely.

You may want to mount a vent fan in the basement window you mentioned to maintain a negative pressere condition in the basement. This would help keep the air upstairs free of fumes. Safety first!