Phosgene

CAS RN: 75-44-5

Odor Threshold

Odor cannot be used as a warning for potential exposure. The odor threshold is reported to be between 0.5 and 1.5 parts per million (ppm) ... and tolerance to the pleasant odor of phosgene occurs rapidly.
The irritant properties of phosgene are not sufficient to give warning of hazardous concn. A trained observer can recognize 0.5 ppm as being "sweet" & at about 1 ppm, the odor becomes typical of the "musty or newmown-hay" smell usually ascribed to phosgene. Workers exposed to phosgene can lose their ability to detect low concn through olfactory fatigue.
One-half part per million can be recognized through the sense of smell, by normal persons acquainted with its odor, but olfactory fatigue or adaptation can cause a gradually increasing concentration to go unnoticed.
0.5 to 1.0 ppm
Recognition in air: 1.00X10+1 ppm /chemically pure/
Find more information on this substance at: PubChem, PubMed