I stumbled across this international study regarding community effects from a large scale NH3 release in 2022. The study wanted to validate or in-validate community complaints years after the event. Residents, numbers unknown, had been complaining of “loss of smell” after being exposed to hundreds of ppm’s of NH3. The study was interesting in that it claimed that some people were incapable of smelling NH3 at 300 ppm (IDLH), but yet could sense their exposure via Trigeminal Sparing. I find this very hard to believe, but the study syas what it says.
When discussing ammonia and olfactory deficits, it is critical to distinguish between temporary sensory adaptation (olfactory fatigue) and permanent physiological damage (anosmia or hyposmia). Ammonia is unique because it stimulates both the olfactory nerve (Cranial Nerve I) and the trigeminal nerve (Cranial Nerve V), which provides the “sting” or burning sensation.