Odors olfactory fatigue

Odors are characterized by quaUty and intensity. Descriptive quaUties such as sour, sweet, pungent, fishy, and spicy are commonly used. Intensity is deterrnined by how much the concentration of the odoriferous substance exceeds its detection threshold (the concentration at which most people can detect an odor). Odor intensity is approximately proportional to the logarithm of the concentration. However, several factors affect the abiUty of an individual to detect an odor the sensitivity of a subject s olfactory system, the presence of other masking odors, and olfactory fatigue (ie, reduced olfactory sensitivity during continued exposure to the odorous substance). In addition, the average person s sensitivity to odor decreases with age. 

Subjective evaluation of odor emission is made difficult by the phenomenon of odor fatigue, which means that after persons have been initially subjected to an odor, they lose the ability to perceive the continued presence of low concentrations of that odor. Therefore, all systems of subjective odor evaluation rely on preventing olfactory fatigue by letting the observer breathe odor-free air for a sufficient time prior to breathing the odorous air and evaluating its odor content. Usually an activated charcoal bed is... 

With regard to the odor threshold for hydrogen sulfide, it should be noted that although odor can be perceived at 0.5 ppb in air, olfactory fatigue can occur at concentrations of 100 ppm or greater causing a loss of odor perception (Leonardos et al. 1969). 

Colorless gas with a strong odor of rotten eggs detectable at 0.005 ppm. However, it can cause olfactory fatigue and the sense of smell is not reliable. Used industrially to produce elemental sulfur, sulfuric acid, and heavy water for nuclear reactors. 

Colorless gas with a "very offensive" odor that resembles decayed horse radish detectable at 0.3 ppm. However, can cause olfactory fatigue and sense of smell is not reliable. This material is hazardous through inhalation and produces local skin/eye impacts. It is highly flammable. 

The range of reported odor thresholds for chlorine is 0.03-3.5ppm however, because of olfactory fatigue, odor does not always serve as an adequate warning of exposure. ... 

Rapid olfactory fatigue excludes odor as a satisfactory early warning device. ... 

The strong peppermint or honeylike odor is detectable at 12 ppm severe overexposure is unlikely because of local irritation and odor however, olfactory fatigue may occur. ... 

Pyridine has an unpleasant odor detectable at Ippm the odor is objectionable to unacclimatized individuals at 10 ppm but does not provide sufficient warning of hazardous concentrations because olfactory fatigue occurs quickly. ... 

Tetrachloroethane has a mild, sweetish odor detectable at 3 ppm that may not provide sufficient warning of dangerous levels because of olfactory fatigue. 

Hydrogen sulfide is a colorless, flammable gas at ambient temperature and pressure. It is an irritant and asphyxiant and has an offensive odor similar to rotten eggs. It has been reported that people can smell hydrogen sulfide at concentrations as low as 0.5 parts per billion (ppb) of air (ATSDR 1999). Hydrogen sulfide has an odor threshold of 0.02-0.13 parts per million (ppm) (Beauchamp et al. 1984). Olfactory fatigue (which causes a loss of odor perception) can occur at 100 ppm, and paralysis of the olfactory nerve has been reported at 150 ppm (Beauchamp et al. 1984). The chemical and physical properties of hydrogen sulfide are summarized in Table 7-1. 

The sense of smell is our most sensitive special sense. We are able to detect the odor of certain chemicals in the parts per million range. However, some chemicals are undetectable altogether, and others cause olfactory fatigue, in which exposure to a substance reduces our ability to detect its odor (e.g., hydrogen sulfide). Even more interesting, certain people are unable to detect certain odors, while others can... 

Few agents are acutely toxic to the olfactory receptors. Hydrogen sulfide, as mentioned earlier, causes rapid olfactory fatigue, and the normal rotten egg odor quickly vanishes allowing prolonged exposure to this potentially fatal mitochondrial toxin. Occupational exposure to several solvents and metals has been associated with olfactory dysfunction (Table 4). 

Acute inhalation exposures may result in irritation of the nasal mucosa and eyes ( 50 ppm), irritation of the skin, and CNS depression (>100 ppm). Symptoms of CNS depression include nausea, drowsiness, and ataxia. The disagreeable odor of styrene, which is detectable at 0.04-0.3 ppm, serves as a good warning aid. However, olfactory fatigue may occur at high concentrations. 

Physical Description Colorless liquid with a strong, disagreeable odor characteristic of mercaptahs. [Note Olfactory fatigue may occur after short exposures. 

C. Warning properties, such as odor and sensory Irritation, can be valuable Indicators of exposure. However, because of olfactory fatigue and Individual differences in odor thresholds, the sense of smell Is often unreliable for detecting many compounds. There is no correlation between the quality of an odor and its toxicity. Pleasant-smelling compounds are not necessarily less toxic than foul-smelling ones. 

If at any time during the test, the subject detects the banana-like odor of lAA, the test is failed. The subject shall quickly exit from the test chamber and leave the test area to avoid olfactory fatigue. 

Odor Strong rotten egg odor detectable at 0.001 to 0.1 ppm (mean = 0.0094 ppm) olfactory fatigue occurs quickly at high concentrations... 

The mixtures used in the lAA odor detection test shall be prepared in an area separate from where the test Is performed, in order to prevent olfactory fatigue in the subject. 

The human being is exceptionally sensitive to some volatiles (e.g., 2-isobutyl-3-methoxypyrazine has an odor detection threshold in water of 0.002 ppb [49] and 0.015 ppb in wine [50] but insensitive to many other volatiles (e.g., ethanol has an odor threshold of 100,000 ppb in water and a taste threshold of 52,000 ppb in water) [49]. A person s ability to detect odors is also influenced by many other factors such as genetic variability, olfactory fatigue, and naturally occurring and unpredictable factors such as temperature and humidity. The complexity of food aromas and sensitivity required plus the fact that the olfactory system must be able to respond to unknown odorants (it cannot be learned response) make this a most complex phenomenon. 

The gas has a pungent odor (most texts state that H2S smells like rotten e s, but, with modern refrigeration, it is probably more apropos to state that rotten e s smell like H2S). It is easily detected by sense of smell up to values of around 100 ppm. Above 100 ppm olfactory fatigue can set in, and most people cannot smell the gas. Therefore, the inability to detect H2S through the sense of smell does not prove that the gas is not present. Moreover, the ability to detect the gas by smell varies widely among individuals. 

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