Cyanide odor threshold

Hydrogen cyanide has frequently been associated with the odor of bitter almonds (Ballantyne 1983 Gee 1987). The threshold odor for olfactory detection of atmospheric HCN is 1 mg/L, but the odor may not be detected for various reasons, including the presence of other odors and the fact that only 20 to 40% of those tested could detect a cyanide odor. 

The odor threshold, 0.58 ppm to 5.0 ppm (Amoore and Hautala 1983 Ruth 1986) is low compared with irritant or toxic concentrations. No acute exposures were located resulting in mild effects in humans. Three monitoring studies, involving no symptoms to mild symptoms during chronic occupational exposures of adult males, are relevant to development of AEGL-1 values. The symptoms and blood concentrations of cyanide in the monitoring study of Chandra et al. (1980) indicate that the workers may have been exposed at higher atmospheric concentrations than those reported. 

An almond-like smell in the breath of a poisoned patient can warn a physician that the individual may be suffering from cyanide poisoning. Approximately 60-70% of the population can detect the bitter almond odor of hydrogen cyanide. The odor threshold for those sensitive to the odor is estimated to be 1-5 ppm in the air. However, even at high toxic concentrations up to 20% of all individuals are genetically unable to smell hydrogen cyanide (Snodgrass 1996). Some effects of cyanide that can also be used to monitor exposure are discussed in Section 2.5.2. 

Hydrogen cyanide is an extremely toxic chemical in both vapor and liquid states. The threshold odor limit for most people is <5 ppm, but the odor is not noxious and often is compared to the fragrance of bitter almonds. It is highly soluble in water. 

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