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| MEASUREMENT OF AGRICULTURAL DUSTS AND GASES
As agricultural workers become aware of the respiratory threats posed by their work environment, they feel a corresponding need to detect and quantify toxic substances. Usually, this is done with gas or dust measuring devices. These devices should be used whenever dealing with situations where a hazard is short-lived (such as when emptying a manure pit underneath a confinement house). When exposure to dusts and gases may be longer lasting, such as in a barn or livestock confinement building, workers should regularly monitor dust and gas build-up and take steps to minimize high concentrations of toxic substances through engineering controls and management changes. Health care workers can play a crucial role by encouraging agricultural workers to use gas and dust measuring devices to decrease the possibility of damage to the respiratory tract. For patients who already have respiratory problems, use of such devices may be psychologically supportive, as well as medically beneficial. Health care workers also can encourage local retailers to stock or rent commonly used devices. This unit provides basic information on measurement that will be useful in working toward these goals. I. MEASUREMENT DEVICES FOR GASES AND DUSTS Almost all of the many measuring devices for gases and aerosolized dusts were developed for use in industry. They range from small personal air samplers that can be attached to a worker's clothing, to hand-held devices, to large permanently installed systems that measure several substances at once. Gas measuring devices The measuring devices best suited to most farm needs are those that give immediate reading of the gas level, and those devices that give a one-time measurement instead of an accumulated measurement over time (dosimeters). In addition, these characteristics should be considered when choosing a gas measuring instrument:
The farmer must match his particular needs with the device that best fits those needs. Cost and ease of operation, as well as shelf life, will be of special concern to farm purchasers. Detector or colorimetric tubes These instruments give a direct reading of the concentration of the gas being measured. A hand-operated bellows pump or a piston-type pump is fitted with a detector or colorimetric tube containing a chemical. (See Fig. 1) Many types of tubes are available, with different chemicals that react to different gases. To operate, the appropriate detector tube is placed in the pump, and the bellows pump is squeezed or the handle of the piston-type pump is pulled back for a specified number of strokes. This draws air through the detector tube, the chemical in the tube changes color, and the concentration of the gas can be read from the scale marked on the tube. A separate tube must be used for each air sample taken unless there is no reaction at all. An extension hose can be placed between the pump and the tube so that the air inside a structure can be measured without the operator having to enter the structure. This basic pump costs about $100. Extension hoses and moderately priced tubes are sold separately. Detector or colorimetric tubes adequately fulfill the farmer's requirements for accuracy, and ease of operation and maintenance. Shelf life of the tubes is two to three years. Dosimeter tubes Most manufacturers of detector tubes also make dosimeter tubes that, like detector tubes, measure gas concentrations by means of a chemical reaction. (See Fig. 2) Unlike detector tubes however, the dosimeter tubes do not give an immediate readout. They must remain exposed to the atmosphere for at least an hour before an accurate measurement can be read from them. This characteristic makes dosimeter tubes unsuitable for several farm uses, since an immediate readout is often needed. Hydrogen sulfide can build quickly to toxic levels during manure pit pump-out, and oxides of nitrogen also can form quickly in newly-filled silos to levels that can be almost immediately fatal. Farmers must have a gas detection device that rapidly measures gases in these and similar situations. When a rapid warning is not needed, such as during monitoring of confinement buildings for ammonia or carbon monoxide, dosimeter tubes are suitable. They are inexpensive for occasional use and are easily attached to a worker's clothing. Solid state detectors These electronic instruments have sensors for detection of various gases. Some of the less expensive brands can be plugged into a standard electrical outlet or are battery operated. (See Fig. 3) Gas concentrations are indicated by lights and/or by alarms that sound when the concentrations reach levels set (usually) by the manufacturer. (See Fig. 4) The devices just described are available for under $200. These instruments may give less consistent measurements than do the detector tubes. They have not been sufficiently tested for use in agricultural operations. More advanced meters with digital readouts are available for $500 and up. Sensors on all of the solid state detectors must be replaced every one to three years. Sensing badges and tapes Several sensing badges and tapes are available that give an indication of gas concentrations by means of a color change. (See Fig. 5) These devices have not been sufficiently tested for accuracy and precision in agricultural operations. They are inexpensive for occasional use, and are easy to operate, attaching to a worker's clothing. Most of these badges are dosimeters and they function like the dosimeter tubes described earlier; they will not give a correct quantitative reading until they have been in the environment for an hour or more. Farmers must realize that neither the badges nor the dosimeter tubes are safe for use where toxic gases may be present in levels immediately dangerous to health. Dust measuring devices Instruments that detect and analyze atmospheric dusts are too expensive for most individual farm operations and require training to operate and maintain. A meter which gives a direct (immediate) reading of the concentration of dusts in the air costs over $1500. An analysis of dust composition requires other expensive sampling equipment, and each sample must be analyzed in a laboratory at a cost of $25 to $100 per sample. Alternative ways of obtaining dust measurements on the farm are listed in Section 111. II. USING GAS MEASURING DEVICES ON THE FARM Gas measuring devices measure the concentration of gas in the air, usually in parts per million (ppm). Exactly what do these measurements mean in terms of human health? The American Conference of Governmental Industrial Hygientists (ACGIH) reviews research on health effects of various concentrations of toxic gases, and then recommends the maximum concentration of each gas to which a worker should be exposed for a certain length of time--called a TLV (threshold limit value). The TLV forammonia is 25 ppm. This means that a worker should be exposed to no more than 25 ppm of ammonia averaged over an 8-hour workday. These TLV's are useful in industrial settings where the atmosphere and the workers can be monitored. Since there are no exposure guidelines available specifically for farm and ranch situations, the ACGlH-recommended TLV's must be used as indicators of potential respiratory hazards (See Table 1). Table 1 Examples of Threshold Limit Values Gas ACGIH TLV's, 1985-86 Nitrogen dioxide (NO2) 3 ppm based on irritation
Hydrogen sulfide (H2S) 10 ppm well below lung damage
level for 10-fold safety factor
Ammonia (NH3) 25 ppm based on irritation
Carbon monoxide (CO) 50 ppm based on headaches
Carbon dioxide (CO2) 5000 ppm based on heart stress
Farmers may need to measure gas concentrations in the following situations. Specific techniques for taking measurements are described in the patient education brochure on measurement of dusts and gases Filling a nonairtight silo [See Unit 5: Oxides of Nitrogen (Silo Gas).] Nitrogen dioxide can be measured with detector tubes or with one of the more expensive solid state detectors. Only instruments with direct readouts are useful. Pumping out a manure storage pit under a confinement building. (See Unit 4: Livestock Confinement Dusts and Gases.) Hydrogen sulfide can quickly reach harmful levels in manure pits and buildings over pits during pumping. Instruments with direct readouts must be used. Monitoring ammonia levels in swine and poultry confinement buildings. Since ammonia levels do not generally change rapidly in confinement buildings, either direct readout instruments or dosimeters (badges, tubes, or tapes) can be used. Farmers may be concerned both about their own health and the health of their animals. Working in a tightly closed building. Although not a common problem, carbon monoxide levels may become hazardous in tightly closed buildings with poorly adjusted direct-fired heaters or when the exhaust gas from indirectfired heaters is drawn back down the stack by exhaust fans elsewhere in the building. Direct readout detection devices should be used. Oxygen-deficient atmospheres. Farmers may want to enter closed storage structures such as airtight silos, underground manure storage pits, or other structures where fermentation processes have depleted the oxygen supply. These structures should not be entered without a selfcontained breathing apparatus or a supplied air respirator with hose mask and blower. Farmers and ranchers typically do not have this equipment or the training to use it so they will occasionally enter closed storage areas without proper protection. Before entering they can measure the oxygen concentration with detector tubes or solid state sensors. III. ALTERNATIVE WAYS OF MEASURING (OR ESTIMATING) GAS, DUST, AND OXYGEN LEVELS If your farm patients are unable or unwilling to purchase measuring devices, some of the following options might be useful. Co-ops and farm supply stores should be encouraged to stock items such as smoke tubes. These businesses also could purchase some air sampling equipment, maintain the devices for customers, and provide them with instructions for use. Businesses that sell measurement devices are listed in the yellow pages under "Safety Supply". Other sources of measuring equipment include veterinarians who often own measuring equipment for use in their practices. Farmers could inquire about using this equipment or hiring the veterinarian to take measurements. A consulting engineer or industrial hygienist could be hired to take measurements, although it may be more convenient or cost effective for a farmer to buy and use the instruments himself. Most governmental agencies are not equipped to do any air quality testing for individual farm operations. The policies of Occupational Safety and Health (OSHA) Consultation Offices vary from state to state. In many cases farmers can avoid danger by knowing what dusts or gases might be found in certain structures and being especially alert to any signs of their presence. People who have been overcome by silo gas often mention that they noticed eye or nose irritation while they still had a chance to escape, but decided to ignore that warning. Farmers who regularly store grain on the farm often can assess the condition of the grain by smelling the air that is being blown through the grain. They may notice that dusts from moldy grain (which are more dangerous than dusts from grain in good condition) have a different odor than dusts from grain that has no spoilage. Encourage your farm clients to learn to pay attention to their senses and trust their experience. When farmers begin to take seriously any signs of danger, they will do much to avoid respiratory hazards. Use of smoke tubes can help farmers indirectly assess problems of dust or gas
build-up in animal confinement buildings. Smoke is released in the building, and
its movement (or lack of movement) enables farmers to identify inadequacies in
the ventilation system. Smoke tubes are sold by the same outlets that sell gas
detector tubes. תתתתתתתתתתתתתתתתתתתתThe National Dairy Database (1992)תתתתתתתתתתתתתתתתתתתת תתתתתתתתתתתתתתתתתתתתת\NDB\OCCSAFE\TEXT2\OF201100.TXTתתתתתתתתתתתתתתתתתתתתתת %f TITLE;MEASUREMENT OF AGRICULTURAL DUSTS AND GASES %f COLLECTION;FARM AND
OPERATOR SAFETY |
