Doesn’t seem like that from the police investigation, though that was my first thought too.
If the woman revives maybe she will know about something that was not still on the scene when help arrived.
My other guess would be they were making Ricin. Just a guess, mind you.
I worked in a pulp plant and I’ve been dosed a bunch with noxious gases. Sulfur dioxide is a near clear gas that will blow you out if you walk into a cloud. Pure chlorine gas you can see, and there are some pine byproduct liquids/vapors that are noxious. Not to mention all the other chemicals used to make high quality pulp.