Std/eng/ info olfactometry OLFACTOMETRY

Transcription

1 Std/eng/ info olfactometry OLFACTOMETRY The olfactive system The olfactive system brings information about chemical environment. Participating in the location of potential food, in congeners' identification, or in establishment of relations of communication with the important consequences on the social organization, the olfactive information controls numerous behavior. The data carrier is not a physical greatness, as an electromagnetic wavelength for the vision, or the frequential variations of pressure for the hearing, but the particular, physico-chemical conformation, the energy, carried by volatile chemicals: the smelling. We soak most of the time in a complex cloud of volatile molecules. Our olfactive system should so extract informations from it. To do it, one can consider that it makes play two offices: discrimination and identification. The office of discrimination allows the extraction of signals in a background noise and a distinction of the signals among them. The office of identification realizes as for it a recognition of these signals, confronting them with stored information, awarding so a meaning to the stimulus. All these offices which lead to the olfactive perception bases on physiological mechanisms which are the reception of the smelling molecules and the olfactory memory. The sensation of smell is created by the olfactive receivers situated at the top of every nasal pit, connected with the intellectual olfactive bulb through the riddled blade. The olfaction is the only sense for which neurones are directly exposed on the outside environment without any protection against the attacks of certain substances. The perception of the smells The perception of a smell results from a very fast, almost immediate stimulus, which contains several information among which, the intensity and the quality of the smell. At the level of the intensity, our smell behaves as for the notion of warmth and cold. The intensity of the signal is important at the beginning of the perception then fall gradually with the adaptation. On the qualitative plan, our smell works as for the tasteful notion. We can recognize, appreciate and classify the quality of a smell. Variations of the olfactive perception The olfactive capacity is stronger in the morning and the susceptibility in the smells varies from an individual to the other one. However, it is notorious that women have a better smell than men and that the not smokers are more sensitive than the smokers. From 60 years old, begins a decline of the sensation, the discrimination and the identification of the smells. More of half of the persons of more than 80 years old have a bad smell among which 25 % of the subjects smell nothing more. The olfactive perception is influenced, for a woman, by sexual hormones. It is increased during the ovulation and at the beginning of the pregnancy. On the other hand, a decline of its smell is observed in the course of menstruation, at the end of pregnancy, and after the menopause. The smell knows also weaknesses. Some persons smell, for example, an odor in the place of another (dysosmia) or still identify a smell which does not exist (phantosmia). The most painful confusion stays the loss of smell (anosmia). The most frequent causes result from a cranial traumatism with destruction of the olfactive nerve, the nasal infections (chronic rhinitises, polyps) or from a disease of Alzheimer during which the "reading" of the smells by the brain becomes impossible. Far from being a minor sense, the smell is a window on the outside which allows to interiorize the world, to remember and to be in connection with the others.

2 The stenches The human smell, although less sensitive than that of the other mammals, is a source of information about chemical substances of the environment. The human nose is capable of recognizing until smells at very weak concentrations in smelling molecules. The analytical technics do not always succeed in reaching such a threshold of detection. We can, for example discover hydrogen sulphide in a content ten thousand times as weak as a toxic concentration. The stenches often contribute to the anxiety of the population as for the quality of air and influence their lifestyle. Because the smells are easily detectable, they are the main motive for complaints. Among the air contaminants, the smells are the most difficult to manage, because of the subjectivity inherent to the measure and to the definition of what would constitute an unacceptable olfactive threshold. The contaminants of air possessing an unpleasant smell is more often annoying than toxic or harmful. The stenches have a real impact on the way of life and the prosperity of people, simple fact that they are annoying, unpleasant or sources of complications. Olfactometry The professional "nose" To measure a smell, the best instrument remains still the nose the olfactive muqueuses of which is a really reliable sensor. The olfactive sensation varying from an individual to an other one, this method is limited. If certain local residents speak " about annoying smell " for emanations of companies of roasting coffee, the others evoke rather a pleasant aroma. However, it is only from human olfactometric measures that a balance of the issues of smells can be drawn up and that the correspondence of the industrial discharges can be controlled. A smell consists of numerous volatile chemical substances. The stenches generated by industrial activities contain between 200 and 800 active principles different. The most frequent are molecules sulphurated in the smell of rotten egg, the nitrogenous molecules from which the ammonia smell and finally the acids, ketones and aldehyds, in the smell bitter and rance. The olfactometry allows to quantify the concentration of a smelling mixture and to determine an intensity of it. The result of the quantifications is made by statistical treatment of the answers of a jury of at least six persons to which one presents the air harvested at a point of issue on an industrial site. The malodorous gas is taken to the source, the chimney for example, and packaged in plastic waterproof balloons. In a laboratory, the sample is then connected on an olfactometer. Inside the device, the gas undergoes successive dilutions with an odourless reference air. The various dilutions are then presented to each of the "noses" who determines the own limit of detection of the smell. The threshold of detection of a smell is so the concentration of substance for which 50 % of the "sniffling" have no more perception of the smell. The results are expressed in unity of smell. For example, 100 units of smell represents the concentration of a smelling gas for which it was necessary to dilute it 100 times so that half of the members of the jury smells nothing more. Recognize a substance by its smell The human vocabulary does not allow to name exactly a smell as it is possible to do it to describe a colour. On the other hand our memory allows us to associate a smell to a lived situation or to a particularly striking event. Here are some remarkable chemical substances that we are in the habit of associating to a name of smell. Hydrogen sulphide Methylmercaptan Rotten egg Cabbages

3 Ethylmercaptan Cabbages in decomposition Allylmercaptan Garlic Ammonia Very prickly, irritating Methylamine Fish in decomposition Indole, scatole Excrement Cadaverine Meat in decomposition Acetic acid Vinegar Butyric acid Butter rance Valeric acid Sweat, perspiration Formaldehyde Acre, close Acetaldehyde Fruit, apple Acetone Sweet fruit Dimethylsulfure Vegetables in decomposition Thiolane Gas (product for odorisation some gas) (This article is about an odour lab in Australia and is not exact similar to other countries, but it provides a general understanding) The laboratory The ILEMS air quality laboratory consists of a Forced-Choice Dynamic Olfactometer, designed and operated to meet the requirements of the Australian / New Zealand Standard - Stationary Source Emissions - Determination of Odour Concentration by Dynamic Olfactometry (AS4323.3)

4 The Olfactometer uses a panel of 8 people (assessors) to evaluate air being presented at 3 ports. 2 ports present clean, odour-free air and the third supplies diluted, odorous air. The port from which the odorous air is presented is chosen randomly. Of the 3 ports - the assessors must select which one contains odorous air. This is referred to as forced-choice as opposed to yes/no olfactometry. The assessors also indicate whether the answer they gave was based on certainty, an inkling or a guess. Only those reponses that are correct and given with certainty are regarded as 'true' for the purposes of data calculation. Dynamic Olfactometry means that we can constantly vary the dilution of the odorous air presented to the assessors. Electronic data capture Assessors enter their responses into individual keypads. The data from the keypads is transmitted to the control computer where it is displayed to the operator, used in calculations of individual and panel thresholds and archived for record purposes. Odour sampling procedures Sampling method The preferred method of sampling for odour is the lung method. The lung method involves placing the sample bag in a sampling drum and a pump is used to create a vacuum in the drum to draw air into the bag. Materials required include: sampling bags (the bags must be impermeable, must not react with the sample and must not contribute odour to the sample); sampling drum and pump.

5 Air can by purged from the bag by pumping air into the drum and increasing the pressure. Before a sample is taken, the sample bag should be primed with a sample of odorous air and then purged to remove the sample. This is denoted under the Australian/New Zealand Standard as 'pre-conditioning'. During pre-conditioning, chemicals from the odorous air can bond with any 'absorption sites' on the sample bag. This pre-conditioning ensures that the concentration in the subsequent air sample is accurate, as no further chemicals can be lost due to 'bonding'. Bags should be conditioned at least once with odorous air before a sample is taken as per the Standard. The Intensive Livestock Environmental Management Services conducts three types of sampling: Ambient sampling Ambient sampling involves using the lung principle to draw air from an ambient source into the drum. Ambient sources include samples taken downwind from piggeries and other odorous sources. Point source sampling Point source sampling follows the same principle as ambient sampling, except that the air samples are taken directly from a chimney or duct (point source). In most cases, air from point sources is a higher temperature than ambient air. Because of this, predilution of the air sample is often required to stop condensation that occurs inside the sample bag when the sample from the point source cools and vapour inside condenses. There are two types of dilution: static and dynamic. Static dilution refers to placing a known amount of dry odour-free air into a bag and then placing a known amount of odorous sample into the bag at a later stage. The air going into the bag is normally measured with gas meters.

6 Dynamic dilution is where a sample of odorous air and a sample of odour-free air are placed into a bag at the same time whilst sampling to prevent condensation in the tubing between bag and the source. Panelists Olfactometry is a procedure that utilises a panel of people (air quality assessors) to assess air quality. Air quality asessors play a very important role in attaining reliable and repeatable olfactometry results. The panel of air quality assessors are required to assess air samples being presented to them. These olfactometry results are then used to determine the concentration and offensiveness of any given sample of air. Selection procedure Air quality assessors are required to consistently meet a defined and measured olfactory sensitivity (i.e. ability to smell) in accordance with the Australian/New Zealand Standard. To determine if a potential assessor meets the requirements, they are invited to undergo an initial olfactometry selection screening. Criteria Air quality assessors must be at least 16 years of age and willing and able to follow instructions. They must also be willing and able to abide by the responsibilities contained in the Rules for Panellists which is outlined below. The reference odourant n-butanol is used to test a potential assessors' olfactory sensitivity and repeatability during the selection screening. They must fall within a defined bandwidth that is narrower than the expected variability within the general population. Ongoing maintenance An air quality assessors' peformance is continually monitored whilst participating in the olfactometry measurements. A measurement history is maintained for each air quality assessor. Every time the air quality assessors sit on the panel for a measurement, an individual threshold estimate needs to be established to ensure that the assessor's olfactory sensitivity and repeatability remain within the defined bandwidth. Rules for panellists The air quality assessors need to observe the following Code of Conduct: The air quality assessor shall be motivated to carry out his/her job conscientiously. The air quality assessor shall be available for a complete measurement session, and preferably for a minimum of three months to establish and monitor a history of measurement. From 30 minutes before and during olfactometry measurements an air quality assessor shall not smoke, eat, drink (except water) or use chewing gum or sweets.

7 Air quality assessors shall be cautious with the type of foods consumed on the day of measurement sessions by avoiding spicy or aromatic foods as these affect the olfactory sense. Air quality assessors shall take great care not to cause any interference with their own perception or that of others in the measurement room by lack of personal hygiene or the use of perfumes, deodorants, body lotions or cosmetics. Air quality assessors taking medication, suffering a cold or any other ailment affecting their perception of smell (eg. allergic fits, sinusitis) shall exclude themselves from participating in measurements. Air quality assessors shall be present in the measurement room 15 minutes before the measurements begin in order to adapt to the environment of the measuring room. During measurements, air quality assessors shall not communicate with each other about the results of their choices. Air quality assessors shall notify the olfactometer operator of their availability to participate on the days olfactometry measurements are to be conducted. They are to confirm with the olfactometer operator their intention to attend at least 24 hours prior to each measurement session. Air quality assessors will verify, by signature, their hours worked at the end of every olfactometry measurement session. The enforcement of the Code of Conduct has a direct influence on the olfactometer measurement results, and is therefore of great importance. Environment and tools There are up to eight air quality assessors on any olfactometry measurement panel. Air quality assessors are seated at individual, partitioned booths within the same room space. In front of each panellist are three funnel shaped ports. The ports deliver air for sampling (ie. smelling). These ports are adjustable so that the most comfortable position for each panellist can be achieved. Each port has a cap which must be lifted and replaced each time air is sampled from a port.

8 A numeric keypad, as in the picture below, is positioned along side each set of ports. The keypad is used for entering individually assigned identification numbers and measurement responses. A screen at the top of each keypad provides simple prompts for the assessor. The keypad prompts, in a simplified manner, mirror the guided instruction given by the olfactometer operator at every step of the measurement process.

9 Quality asurance The ILEMS Olfactometer has been developed to meet the Australian/ New Zealand Standard - Stationary Source Emissions - Determination of Odour Concentration by Dynamic Olfactometry (AS4323.3). This ensures accurate and reliable odour determination for air samples. Laboratory The ILEMS air quality laboratory (which houses the Olfactometer) is completely odour free. The laboratory is situated away from buildings and any odour sources, and is made from odour free materials. The laboratory is regularly cleaned to ensure no odours are present, and is ventilated with a recycling air conditioner to ensure a constant temperature. Olfactometer The ILEMS Olfactometer is entirely made from stainless steel and Teflon. The machine has a multiple filtered odour-free air supply with mass flow controllers. The controllers ensure accurate measurement of odorous air passing through the Olfactometer. The Olfactometer has a step factor of 2, which falls within the bandwidth given by the Standard ( ). This means that the odour concentration is doubled each time the odour is presented to panellists. Panellists The panellists are screened each session to ensure their n-butanol thresholds stay within a defined range. The Australian/New Zealand Standard for Olfactometry states that the accuracy of the n-butanol must stay within 5% of the reference concentration (i.e. the concentration used should not vary over time). ILEMS uses n-butanol with a 1% or better accuracy.