The human nose can detect ammonia at concentrations as low as 3.5 mg/m³, which is equivalent to 5 ppm

 The human nose can detect ammonia at concentrations as low as 3.5 mg/m³, which is equivalent to 5 ppm. While the odor threshold is low, higher concentrations can cause irritation to the eyes, nose, and throat.

Here's a more detailed breakdown:

Odor Detection:

The human nose can detect ammonia at around 3.5 mg/m³ (5 ppm). 

Irritation:

At higher concentrations, ammonia can cause irritation. For example, at 25-36 mg/m³ (35-50 ppm), it can irritate the eyes, nose, and throat after a 2-hour exposure. 

OSHA PEL:

The Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit (PEL) of 50 ppm (35 mg/m³) averaged over an 8-hour work shift. 

NIOSH REL:

The National Institute for Occupational Safety and Health (NIOSH) recommends a limit of 25 ppm (18 mg/m³) averaged over a 10-hour work shift, with a short-term exposure limit of 35 ppm (27 mg/m³) not to be exceeded during any 15-minute period.