How to remove varnish<br>Create good ventilation. Whether your sanding or using a chemical solvent, it's a good idea to have ventilation. Open windows and use fans to create cross-ventilation if you're inside.
It is healthier to remove varnish in a ventilated area.
It is healthier to remove varnish in a ventilated area as opposed to an area that contains the fumes.  They system was likely confused by the comparison.