Instruction 0023-9125 Page-5
ODOROMETER
6. The observer must be careful to hold his nose within one inch of the
SNIFFING FUNNEL to avoid dilution with the surrounding air
(placing the upper lip on the handle will allow the nose to be cen-
tered about one inch above the SNIFFING FUNNEL).
7. Odor level rating must be based on the fi rst sniff or two because the
olfactory senses fatigue rapidly with continued exposure to an odor.
8. Between sniffs the observer should breathe deeply but slowly
through his nose to “regenerate” his perception.
1. Have the observers sniff the unodorized air stream.
2. Adjust the gas fl ow rate to the estimated threshold value and let the
observers sniff again to see if they can smell any foreign odor.
3. Adjust the gas concentration upward or downward, as indicated by
the above test, and have the observers sniff again.
4. Repeat this procedure until the threshold value is obtained for each
observer. It is best to take several readings on both sides of the
threshold and to run an occasional blank using air with no added
gas.
5. Calculate the average threshold value of each observer. Then
calculate the total average value, using these individual averages.
This procedure is advisable because considerable variation is found
among individuals in detecting threshold value. Thus, if the observ-
ers take different numbers of readings, a “straight” average of all
these values would give more weight to the observer with the larger
number of readings.
6. It is essential for this type of determination that the odor level rat-
ing be based on the fi rst sniff only, because fatigue is very rapid in
this range.
1. Have the observers sniff the unodorized air stream.
2. Adjust the gas rate to the desired concentration.
3. Have the observers sniff the effl uent air stream, rating the odor in-
tensity as (1) absent, (2) barely detectable, (3) readily detectable, (4)
strong, (5) very strong (obnoxious).
4. If desired, a description of the character of the odor, such as onion,
garbage, refi nery, etc., can also be obtained.
5. Repeat the test after a short time to check the fi rst determination.
4. THRESHOLD
ODOR
DETERMINATION
5. ODOR
CHARACTERISTICS
AT STANDARD
CONCENTRATION
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