NIOSH issued a formal Request for Information (RFI) seeking new toxicological and human health effects data to refine the established IDLH value for ammonia (NH3), which currently sits at 300 ppm. The agency is specifically looking for updated “weight-of-evidence” research on how ammonia’s chemical mode of action—particularly rapid desensitization of olfactory receptors (smell fatigue) and severe eye/throat irritation—affects a worker’s ability to self-evacuate before physiological impairment occurs. A revision to the ammonia IDLH could alter mandatory respirator selection logic across refrigeration, fertilizer manufacturing, and chemical processing industries, potentially lowering the threshold where full-facepiece pressure-demand Self-Contained Breathing Apparatus (SCBA) or supplied-air respirators (SARs) become mandatory.