I spent a lot of years in the lab. The olfactory sense is amazing. For many things you can smell (detect a few parts/million) it way before you get to harmful levels Ammonia is one of those things. If you smell it and ventilate the levels will be way below toxic. Just consider how strong the smell is when you open a bottle of household ammonia. I used to use a gentle sniff to clear up a stuffy nose when I had a cold.
Bottom line -- Don't worry about ammonia. It will annoy you and you will clear it out long before it gets toxic.
John
I had a problem ship come into port to load caustic soda after having urea on it last cargo. Ship said they washed according to wash methods which for urea was basically how water wash with sea water then fresh water rinse.
Part of my job as cargo inspector is to make sure the vessel tanks are clean and suitable for loading. This means to "pop" all the ship load lines with air to blow out anything in them like last cargo residue etc and then go into the vessel tanks to see how they are as for cleanliness.
We blew all the lines and they were clear and free of last cargo. No smell or residue. The tanks were clean dry and odor free as well. When we hooked up the load arm to the ship manifold, the resulting sample at that point prior to allowing the liquid cargo to enter ship had a strong odor of ammonia. To the point it made your eyes water. The lab said was only 2ppm contaminant in it. Dry urea has no smell. The mainifold connection was stainless steel and we took the connection loose and washed with water and reconnected only to have same thing happen! Urea is pretty strong obviously. We wound up flushing all lines with caustic soda and disposing of that cargo and thankfully had no problem with the tanks themselves.
Point is that 2 parts per million in this case is enuff to be noticed by some. In the lab 2 of the 3 people could not smell the ammonia.