Phosgene

Suffocating odor; when diluted with air there is an odor reminiscent of moldy hay

Odor varies from strong and stifling when concentrated to hay-like in dilute form

Characteristic odor; the odor of the gas can be detected only briefly at the time of initial exposure. At about 0.5 ppm in air, the odor has been described as pleasant and similar to that of new-mown hay or cut green corn. At high concentration, the odor may be strong, stifling, and unpleasant.

Suffocating odor like musty hay