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. 

Severe headaches occurred in an individual exposed to diesel fuel vapor for 10 days (Reidenberg et al. 1964). Anorexia occurred in a man following dermal and/or inhalation exposure to diesel fuel over several weeks (Crisp et al. 1979). Other neurological effects were reported following inhalation of JP-5 vapor in two individuals who had fatigue and coordination and concentration difficulties other effects included headache, apparent intoxication, and anorexia. Effects subsided within 24 hours for one individual and within 4 days for the other (Porter 1990). Sensory impairment did not occur in these individuals. However, experimental data indicate that olfactory fatigue and taste sensation may occur in some individuals after a 15-minute inhalation exposure to 140 mg/m deodorized kerosene vapor (Carpenter et al. 1976). These data suggest that the different types of fuel oils may behave differently under inhalation exposure conditions. The effect of deodorized kerosene may also occur at lower doses, but this cannot be determined from these data. 

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. ... 

Voluntary human exposure to 1 ppm for 7 minutes produced mild eye and throat irritation olfactory fatigue occurred in one subject within 24 minutes, but no fatigue occurred during a 30-minute exposure at 5.5ppm. Workers accidentally exposed to vapors for 5 months experienced headaches during the first... 

Abdominal cramps, vomiting, and diarrhea occurred in a truck driver who was exposed to diesel fuel vapor for 10 days while driving a truck with a leaking fuel injector. Acute renal failure was also observed. One case study describes eye irritation in two individuals exposed to JP-5 fuel (kerosene) for approximately 1 hour while flying an airplane. Coordination and concentration difficulties were noted, as were headache, apparent intoxication, and anorexia. Inhalation of 140mg/m deodorized kerosene by six volunteers caused olfactory fatigue in three subjects and a taste sensation in... 

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. 

In human tests, exposure to 880 ppm (4100mg/m ) for 15 minutes resulted in eye and throat irritation with olfactory fatigue. The chief effect of exposure to high levels of the vapor is reported to be CNS depression. However, in an accidental brief exposure of 19 workers from an overheated solvent tank, the chief effect was dyspnea, which lasted for several minutes after the exposure. Two of the workers were cyanotic with tremor and nausea, but these were of brief duration. The absence of CNS depression was noteworthy. 

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. 

Olfactory fatigue, paralysis of olfactory nerve. Respiratory irritation, pneumonia from prolonged exposure, acute conjunctivitis, pain lacrimation, photophobia progressing to keratoconjunctivitis, vesiculation of the corneal epithelium,... 

Skin contact with petroleum solvents can cause allergic contact dermatitis. Preexisting skin disease may increase the potential for adverse effects. Overexposure via inhalation of petroleum ether affects primarily the CNS. Short-term, high overexposure is associated with an excitatory phase followed by a depressive phase. Exposures of 100-400 ppm for 7h have resulted in headaches, fatigue, and incoordination with dose-associated effects on equilibrium, reaction time, visuomotor coordination, and memory. Inhalation exposures of 445-1250 ppm resulted in blurred vision, a cold sensation in extremities, fatiguability, headache, fatty demylination of muscle fibers, and demylination and mild axonal degeneration. Exposure to 880 ppm produced eye and throat irritation with temporary olfactory fatigue. 

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. 

Inhalation Nose and throat irritation with cough and hoarseness. Olfactory fatigue may develop after continuous exposure. 

In a study of sensory threshold of deodorized kerosene in humans, six volunteers 20 to 63 years (yr) old, were exposed to kerosene at 140 mg/m3 (20 ppm) for 15 min. No eye, nose, or throat irritation was reported during or after exposures. Three volunteers reported slight olfactory fatigue (Carpenter et al. 1976). 

ACUTE HEALTH RISKS irritation to eyes, nose, and throat olfactory fatigue corneal edema distortion of vision blue-gray vision optical halos drowsiness cough labored breathing shortness of breath abdominal pain vomiting diarrhea may cause severe sore throat and redness of mucous membranes exposure to high concentration may result in death. 

ACUTE HEALTH RISKS irritation of eyes, skin, and respiratory system lacrimation conjunctival pain photophobia kerato-conjunctivitis comeal vesiculation dizziness headache fatigue breathing difficulty coughing convulsions rapid olfactory fatigue coma death. 

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. 

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