|Printed Text = 26 pages|
The following pages (123 - 140) are from the Certification Training Manual for the Structural Pesticide Applicator published around 1975.
Since then, standards for safety, detection and application may have changed. Examples of these standards found in this leaflet are:
Most of these items have been underlined and marked in red. Check these kinds of items to make sure that they are up to date by checking the label of the fumigant you are using or by consulting with the fumigant manufacturer or distributor for the latest information.
You should also study (1) the Vikane Fumigation Manual [published by the Dow Chemical Company] and (2) "Wood Destroying Organisms".
Also, add to your training in structural fumigation by attending one of the annual seminars presented in Hawaii by the Dow Chemical Company. Contact your Vikane distributor for more information.
Fumigation can be defined as the use of gaseous poisons to kill insects or other pests. Their application is generally limited to plants or products in tight enclosures or those which can be enclosed in relatively gas tight tents or wrappings or to soil. These categories obviously encompass a wide range of commodities and conditions. Many of these are beyond the scope of this text and will not be presented. The intent of this section is to discuss the common fumigants used in the pest control industry and to alert the reader to the methods, materials and techniques used in structural fumigation.COMMON FUMIGANTS
Methyl bromide is a colorless, odorless gas at room temperature which is approximately 3.3 times as heavy as air. It is slightly soluble in water and is nonflammable. In fact it has been used as a fire extinguishing agent. Methyl bromide comes in pressurized cylinders (hence in liquid form) and when used in structural fumigation is usually dispensed through a heat exchanger. Its vapors can be detected with a halide gas detector, and concentration can be measured with a conventional thermal conductivity gas analyzer. It has been successfully used in structural, warehouse and mill fumigations. Methyl bromide has good penetrating qualities and will kill insects in all stages, including adults, larvae, pupae and eggs. Dosages for insect control is usually 2 to 3 pounds per thousand cubic feet. For rodents use l/4 pound per 1,000 cubic feet for 6 hours exposure.
Following is a list of items to be removed before fumigating with methyl bromide. This is only a partial list. When in doubt, pre-test a portion of material to be fumigated.
Unfortunately, from a toxicological viewpoint methyl bromide is highly toxic to man and animals. Because of its high toxicity, high volatility and lack of warning properties such as odor and irritation, it is quite hazardous to handle. Handling and use, therefore, must be carried out in such a way that exposure does not occur or is limited in intensity to levels known to be safe. The addition of chloropicrin as a warning agent is required by regulation in some usages and is prohibited in others, particularly if food is involved.
The initial symptoms after excessive exposure to methyl bromide are usually headaches, dizziness, nausea, vomiting, weakness and collapse. These symptoms may be followed in from 2 to 48 hours by the more serious effect, lung edema. If death results, it is likely to be from this cause. If the person survives the lung edema. complete recovery is to be expected. The typical symptoms resulting from excessive chronic (repeated) exposures usually include blurred vision, staggering gait, mental imbalance, and psychosis. Here again, if injurious exposure isn't excessive, recovery is complete but may take an appreciable period of time.
The most recent threshold limit value for methyl bromide as specified by the American Conference of Governmental Industrial Hygienists is a ceiling of 20 parts per million. This means that in all probability, persons can tolerate up to 20 ppm, but no more, of methyl bromide 7 to 8 hours a day, 5 days a week, for a prolonged period of time without adverse effects. If the daily periods of exposure are shortened substantially or the frequency of exposure is lessened, the amount in the air which can be tolerated will be greater.
It is well known that blood bromide levels rise as a result of either acute or chronic exposures to methyl bromide and this provides one means of diagnosis of suspected cases of poisoning. Blood bromide levels can rise from many other causes, so one has to be very careful in interpreting blood bromide levels. A normal person who is not exposed to bromides of any sort, either swallowed or inhaled. will have a blood bromide concentration of less than l milligram percent (1 milligram of bromide per l00 millileters of blood). If a blood level in the range of 5 milligrams percent were found, some exposure to bromine-containing compounds has definitely occurred. This should be a warning signal and should indicate that the source of this bromide should he determined. If it is due to inhalation of methyl bromide then the technique employed in fumigation are faulty. If it can be associated with the ingestion of bromine containing drugs, then this value is of no significance in evaluating exposure. Blood bromide levels in the neighborhood of 10 milligrams percent definitely attributable to methyl bromide exposure are approaching a serious level. If these levels rise to 15 or more milligrams percent, it is quite likely that serious symptoms of methyl bromide poisoning will appear.
Bromide concentrations derived from the administration of drugs can result in blood bromide concentrations several times these without any adverse effect. In fact, blood concentrations have to exceed 100 milligrams percent before evidence of a condition known as bromism becomes apparent in most individuals. Certainly blood levels significantly less than 100 milligrams percent present no problem when the bromide is derived from such materials. Thus it can be seen that it is extremely important and absolutely essential that the source of bromide in the blood be ascertained before its significance can be evaluated.
It is suggested that men who routinely are employing this type of fumigant be checked at least once a month to determine their blood bromide levels. If analysis reveals that the bromide content of blood from these individuals is low, that is, definitely less than 5 milligrams percent, it is an indication that the men are exercising a reasonable degree of care in their work. If they are above this level, it indicates that an investigation should be conducted as to the source. Such information not only will serve as a protection to the individual and give him reassurance that he has not received excessive exposure, but also it will give the employer reassurance that his employee has been operating in a safe manner or indicate that more care must be exercised in future operations. If a person should become ill or have reason to suspect excessive exposure and has been handling methyl bromide, it would be well to have a blood sample taken promptly for bromide determinations. If the bromide level is found to be excessive, there is reason for concern. If it is not, then one can rest assured that the person has not had an excessive exposure to methyl bromide.
Methyl bromide, if confined to the skin beneath a covering such as tight clothing or shoes, is capable of causing a burn usually characterized by the formation of a large blister. This can also occur from wearing bandages or adhesive tape when exposure is to methyl bromide vapors. In such cases, the vapor is absorbed in the adhesive or bandages thus resulting in prolonged contact with the skin. Therefore, it is recommended that no bandages be worn when handling methyl bromide and that precautions be taken to avoid contact with the liquid. Methyl bromide is poorly absorbed through the skin and hence under practical operating conditions does not present a hazard of systemic effects from exposure on the skin.
Vikane fumigant is a compressed gas with a wide range of biological activity, containing sulfuryl fluoride as its active ingredient. It is practically insoluble in water, stable to heat and non flammable in atmospheric concentrations. It possesses remarkable penetrating powers and has a boiling paint lower than any other fumigant. Due to its high vapor pressure, it diffuses rapidly. It requires no special equipment for dispensing, is relatively unreactive to household effects and to date has shown no odors or staining when used under normal conditions. No corrosion has appeared in fumigated materials.
Its presence is detected with the Davis Detector. Thermal conductivity units are used to measure concentration. Manufacturers provide instrumentation to calculate tailored dosages.
Following is a list of items to be removed before fumigation with Vikane:
The high volatility of Vikane precludes adverse effects upon the skin except for possible "frostbite" should a container be discharged directly on the person. Because of its high vapor toxicity, high volatility, and lack of wanting properties, such as odor and irritation, handling and use must be carried out in such a way that exposure does not occur or is carefully limited to concentration known to be safe. The use of chloropicrin as a warning agent prior to fumigation is generally recommended in all fumigations with sulfuryl fluoride and is required by regulation in many areas. Since sulfuryl fluoride has a very rapid diffusion rate, aeration of structures is rapid and the hazard to occupants after appropriate aeration is nil.
Based upon extensive studies on animals, sulfuryl fluoride is one half to one third as acutely toxic as is methyl bromide. Excessive single exposures can result in tremors with subsequent severe convulsions. Recovery of surviving animals is generally rather rapid. Sulfuryl fluoride has been shown to have a rather high toxicity on repeated exposure. Kidney and lung injury can occur from excessive repeated exposure. The gas is not irritating to the eyes or skin, and it has been shown that undiluted sulfuryl fluoride gas is not absorbed through the skin. The low solubility of sulfuryl fluoride in foodstuffs minimizes the likelihood of ingestion of toxic amounts. However, good practice requires that foods should be removed from the house prior to fumigation or else sealed in tight containers such as plastic bags or refrigerators.
Chloropicrin is often used as a warning agent in the odorless fumigants at the rate of 1 ounce per 15,000 cubic feet. It is also an effective fumigant in some situations. The primary toxic effect of Chloropicrin to humans is irritation of the respiratory tract. An individual will probably not willfully tolerate concentrations which are acutely toxic.
Carbon disulfide is a colorless liquid which is highly volatile. It forms a heavy vapor that has an unpleasant odor. It is seldom used in the home but has some value in fumigating ant hills and grain bins. When used alone, it presents a very serious hazard of fire because of its low ignition point. Most compositions are designed so as to minimize or eliminate the fire hazard. The principal toxicological hazard is from inhalation of vapor but the liquid material also presents a real hazard of skin irritation, particularly if exposure is frequently repeated. Absorption of toxic amounts through the skin from contact with the liquid can occur but the hazard would seem to be small unless exposure were severe and repeated. Excessive single exposures by inhalation may cause unusual fatigue, headaches, visual disturbances, nausea, vomiting, loss of memory and depression up to unconsciousness and death.
The most important effects of repeated sublethal exposures are neurological. These may be manifested in a variety of ways but coldness and heaviness of limbs, tenderness of nerve trunks, polyneuritis, loss of memory, ant varying degrees of depressive psychosis are typical symptoms. Injury to the brain is the typical lesion observed upon microscopic examination of tissues. Although it has been generally accepted that vapor concentrations of carbon disulfide should be maintained below 20 ppm for prolonged ant repeated exposure, recent observations on humans exposed for many years to carbon disulflde vapors in Italy suggest that 10 ppm would be more appropriate guide for control.
Hydrogen cyanide gas, at one time, was one of the most commonly used fumigants. However, this is one of the most toxic and hazardous fumigants. Because of its toxicity and the availability of superior chemicals, the use of this material has been prohibited in most states. The acute toxicity of hydrogen cyanide to man occurs very rapidly, and usually, if they do occur, there is a considerable finality associated with them. The action of hydrogen cyanide is primarily that of inhibiting certain body enzymes which have to do with oxygen transport. However, there have been a few reports of neurological abnormalities resulting from exposure to hydrogen cyanide. Death results from asphyxiation. The probability of chronic effects occurring is slight; the problem is to prevent exposure to acutely toxic amounts of the material. The concentration generally accepted as safe for repeated 8-hour exposures is 10 ppm. Hydrogen cyanide can be readily absorbed through the intact skin in lethal amounts as a result of contact with liquid material or the gas. It is believed that a sweaty person is more vulnerable because the gas dissolves in the sweat from which it is absorbed more readily.
Acrylonitrile is a clear liquid and as a gas is inflammable in high concentrations. When mixed with carbon tetrachloride, it has been used as a spot fumigant in elevator boots. The acute toxicity to man appear to be very similar to those of hydrogen cyanide although the material is not as toxic as hydrogen cyanide. Acrylonitrile is metabolized in the body, but slowly, to hydrogen cyanide. The material may be absorbed either through the lungs or through the skin, and if exposures are excessive, high concentrations of cyanide result ant the effects are essentially the same as with HCN. Symptoms include increased respiration rate, salivation, nausea, excitability, vasodilation, cyanosis, and terminal coma in critical cases. For repeated daily inhalation, a vapor concentration of 20 ppm is considered safe.
Ethylene dichloride is normally used in combination with carbon tetrachloride for the control of insects in grain. It is usually mixed 1 part of carbon tetrachloride to 3 parts ethylene dichloride and is slow to vaporize and requires long exposure periods.
It is rarely used by itself because of its flammability. Ethylene dichloride is somewhat more toxic acutely to animals than is carbon tetrachloride. Experience indicates, however, that most people will not tolerate or will become nauseated by sublethal concentrations. It is believed that for this reason, there have been few, if any, fatalities or even serious illnesses due to ethylene dichloride. Acutely, it is a central nervous system depressant and lung irritant. Chronically, ethylene dichloride is a safer material than carbon tectrachloride. The ACGIH Threshold Limit value for repeated 8-hour exposures has been established at 50 ppm. It has the ability to cause injury to the liver and kidney from either excessive single or repeated exposures.
Ethylene dibromide is a colorless liquid used as a constituent of grain fumigants and a soil fumigant for subterranean termites. It is nonflammable and its vapors are non-explosive. It has good penetrating qualities and is toxic to grain insects.
Ethylene dibromide is actually somewhat more toxic than methyl bromide. The fact that it is a liquid under ordinary circumstances and that it has a distinct odor that is detectable at a concentration of 25 ppm makes it considerably less hazardous to handle than methyl bromide. The ACGIH Threshold Limit value for repeated 8-hour exposures for ethylene dibromide is 25 ppm as a ceiling value. Ethylene dibromide, as well as methyl bromide, is a skin irritant. Spillage on the shoes or on the clothing where the fabric is in close contact with the skin will almost invariably result in the formation of huge blisters unless it is promptly and thoroughly removed. The vapor of ethylene dibromide is not absorbed through the skin to any significant degree, but liquid ethylene dibromide can be absorbed through the skin in toxic amounts.
This material is a colorless liquid which will vaporize at room temperature. It is shipped in steel cylinders and is often used in combination with carbon dioxide due to its vapors being flammable. It is used at the rate of one part ethylene oxide to 9 parts carbon dioxide to form a commercial product known as carboxide. Ethylene oxide is popular in vacuum chamber fumigation.
Because of the flammability and chemical reactivity of this material, the fumigator must be familiar with the special technique required for handling without accident in addition to being aware of the toxicological hazards. The primary toxic hazard of ethylene oxide is that of inhalation of the vapors but skin and eye contact can also be injurious. If small amounts of liquid are allowed to evaporate freely over the skin, irritation does not appear to occur.
Methylene chloride is one of the least toxic of the chlorinated hydrocarbons. If allowed to evaporate from the skin, it produces only a mild tingling sensation. If confined on the skin beneath bandages, inside of shoes, or other clothing, it can cause considerable discomfort and irritation. It is not absorbed through the skin in toxic amounts. High concentrations of the material can be anesthetic but the concentration must be several thousand parts per million before the effects become pronounced. The material possesses very little ability to cause liver injury. Animals have been exposed repeatedly for 7 hours per day for months to 5000 ppm with only questionable adverse effects. A threshold limit value of 500 ppm is recommended for repeated 7- to 8-hour daily exposures. Acute exposures should be limited to those which do not cause anesthetic effects.
Naphthalene is familiar as moth balls and moth crystals. It is a rather weak fumigant and repellent. Injury is not likely to occur from inhalation of naphthalene unless the material is handled at high temperatures. Skin and eye contact do not present a serious problem with naphthalene but repeated ingestion can result in cataracts.
Paradichlorobenzene is used as a weak fumigant and moth repellent. The hazard from inhalation of vapor, eye or skin contact, or ingestion in this usage is not significant. Ingestion of large quantities could, of course, be injurious. Industrial experience has shown that for short periods, the warning properties of the vapor are adequate to prevent overexposure.
Perchloroethylene (tetrachloroethylene) is used in small amounts as a commodity fumigant. It is a good solvent and hence may cause dryness and cracking of the skin if exposure is prolonged or frequently repeated. The liquid is only slightly irritating to the skin and eyes but may cause some pain if it is splashed in the eye. The vapors can cause incoordination as well as more pronounced anesthetic effects depending upon the severity of the exposure. Repeated exposure to excessive concentrations can cause liver injury. It is good practice to limit exposure to a maximum level of 200 ppm with the average at no more than 100 ppm.Propylene Oxide
Propylene oxide when mixed with carbon dioxide is occasionally used in commodity fumigation. This chemical presents chemical, toxicological and flammability hazards comparable to but less than those of ethylene oxide.
Carbon tetrachloride is an excellent solvent. It is used as a flame depressant when mixed with other fumigants but due to its toxicity to man in both liquid and vapor form is rarely used as a household fumigant.
Aluminum phosphide, a solid, is formulated in tablets and pellets which are distributed throughout the commodity to be fumigated. These tablets slowly react with moisture to release phosphine gas (PH3) and a "protective gas."
Phosphine is highly toxic for both single and repeated exposures. The effects of single exposure to phosphine are a feeling of coldness, pain in the diaphragm, nausea and vomiting. Shortness of breath, weakness, dizziness, bronchitis, edema, convulsions, and death can occur if the exposure is excessive. The chronic effects of phosphine are reportedly the same as those of phosphorous: gastrointestinal upset, jaundice, and nausea. The currently accepted threshold limit value for repeated 1- to 8-hour daily exposure to phosphine is 0.3 ppm. Rubber gloves are recommended for handling the pelleted formulations.
All fumigants have appreciable toxicity towards humans and animals, but since they differ considerably, it is difficult to write general instructions for fumigating procedures. In all cases. the fumigator must read and understand the manufacturer's label, and use only as registered thereon. If the instructions on the label are not adequate, the fumigator should obtain more detailed instructions from the supplier or manufacturer. The supplier and manufacturer are obligated to provide adequate information to the user as to toxicity and handling and may be expected to do so if requested.
The symptoms described as resulting from excessive exposure to most of the fumigants in this article are nonspecific in that they are observed in many different illnesses. The diagnosis of poisoning due to a fumigant as opposed to a diagnosis of illness resulting from natural causes can be made only by a physician who is capable of objective consideration of all the facts that can be developed from an examinatinn of a patient and a consideration of possible exposure. This objectivity is important. Self-diagnosis is dangerous even for the well-trained. The best policy is always to report any illness to the physician.
Information concerning the effects of a chemical as well as the symptoms to be expected should be known to the local physician prior to the use of the fumigant. This kind of information can be obtained for the doctor from the supplier of the fumigant. The supervisor of the fumigation should make it a point to get the information from the supplier and transmit it to his physician before using the material. The advantages of this are that it allows the physician time to examine the literature prior to any difficulty and to procure needed supplies.
Every person who is working with fumigant materials should be well informed regarding the hazard of the materials, the appropriate protective devices to be used with each and the limitations of such devices. A choice of a gas mask depends upon the material to which the person is likely to be exposed. the intensity of exposure anticipated and the availability of an adequate oxygen or air supply. Small respirators equipped with cartridge-type canisters are effective in the same way as full-face masks but the capacities are much smaller and they give no protection to the eyes where irritants or lacrymators are encountered. An ordinary full-face gas mask with a suitable standard or large size canister is effective against vapor concentrations up to 2% by volume in air. The duration of the use of a canister must not exceed 20 minutes. Both the respirator and the gas mask can be used only where the oxygen content of the air is not depleted to less than 16%.
A self-contained breathing apparatus is by far the most dependable protection against toxic vapors. This equipment utilizes a tank of compressed air or a special canister in which oxygen is generated during usage. This self-contained equipment should be used if there is any possibility that vapor concentrations are in excess of 2% or if the oxygen content of the air may be too low. It is further evident that any person entering a pit or tank must also wear a safety belt and a rope and have one or more persons remain outside to pull him out in case of accident. There must also be a self-contained breathing apparatus with the watcher. Persons should never work alone in any hazardous operation.
The choice of a canister to be used with a fullface mask or a respirator depends upon the toxicant involved. An organic vapor canister is designed to provide protection against such materials as methyl bromide, ethylene dibromide. carbon tetrachloride, ethylene dichloride, chloropicrin, carbon disulfide, and similar substances within the limitations mentioned previously. For protection against sulfur dioxide, an acid gas canister must be used. For acrylonitrile, a canister designed for both organic vapors and acid gases is recommended. For protection against hydrogen cyanide, phosphine and sulfuryl fluoride, special canisters must be used. Read the instructions on the fumigant label. In all cases, the recommendations of the manufacturers of the fumigants, canisters and masks should be followed.
It is the responsibility of the person in charge of fumigations to see that an adequate supply of canisters and other necessary safety equipment is available before beginning a fumigation. This equipment should be inspected and tested prior to starting each fumigation. All used canisters should be destroyed. The use of halide leak detectors, Thermal Conductivity Units (TCU) or other equipment for the detection and estimation of the concentrations of fumigants is recommended to prevent excess exposure.
The methyl bromide label prescribes the amount of fumigant to be used at varying temperatures and volumes of the structure. Therefore it only becomes necessary to accurately compute the cubic content of space to be fumigated. Warning agents are usually included with methyl bromide; if not, the amount necessary is indicated on the label. The label will also prescribe the release rate, size of the releasing tube and the point of application. Gauges are available which will measure the amount of methyl bromide released at any point in time.
In order to interpret the correct dosage for fumigation with Vikane, a Fumiguide "B" slide rule (Figure 1 ) is extremely handy. A number of factors will influence the amount of Vikane to be used. Each of these conditions have been given a value factor on the slide rule. The conditions must be an estimate by the fumigator based on his expertise. Table 13 shows an example. By starting with the arrow and hairline slide both at 12 on the (HLT) scale, multiply each product by successive factors by first moving hairline slide to estimated condition, then moving center slide to line up with hairline slide. Do not return either slide to starting position until last product has been multiplied. After having moved first the hairline slide, then the arrow in alignment with hairline through all the estimated conditions, the arrow and hairline will both point to the half loss time on the top scale.
Figure 1. Fumiguide "B" Slide Rule for Computing Dosage with Vikane
|Tarp or Stucco Condition||Excellent|
|0.9 x 12 = 10.8 hours|
|0.8 x 10.8 = 8.64 hours|
|1.0 x 8.64 = 8.64 hours|
(1,000 cu. ft.)
|1.2 x 8.64 = 10.4 hours|
0.7 x 10.4 = 7.3 hours
To convert the number of ounces per thousand cubic feet to pounds, turn the Fumiguide "B" over again and refer to the "A" and "B" scales at bottom. Place the arrow of "A" scale over ounces on "B" scale, then move the hairline slide to volume on "A" scale, and read number of pounds under hairline slide on "B" scale. Try working the problem on the following page. Your answer should read 7.3 half loss time.
A warning agent is always used with Vilcane. It is not mixed with the fumigant due to the varying dosages of Vikane. The specific amount to be used is indicated on the label. Vikane dosage is best measured by placing cylinder on scales and after balancing the weight of the cylinder, adjust the scale to the desired amount and when this point is reached the scale will re-balance and valve can be closed (Figure 2).
Vikane Dosage Can
Best Be Measured
By Placing Cylinder
on Scale when Releasing
Because of the varied uses of Phostoxin, only a general outline of instructions can be included in this manual. The needs of the fumigator for a commodity fumigant will necessarily lead him to request special instruction from the manufacturer's agent or distributor for specific uses in fumigations where unusual conditions may be encountered.
Phosphine gas released by Phostoxin is highly toxic to all forms of animal life. Phosphine, also called hydrogen phosphide is a compound having 1 phosphorus atom and 3 hydrogen atoms, thus the formulat PH3. The ingredients are:
|Active ingredient - Aluminum Phosphide
Inert ingredients - Amonium Carbamate
Inert ingredients - Edible Paraffin
The fumigating action is accomplished by the release of gaseous phosphine, through the decomposition of the tablets or pellets. This decomposition takes place in the following manner. The ammonium carbamate reacts with the heat in the atmosphere and starts the decomposition. This allows the moisture in the atmosphere to penetrate the aluminum phosphide which reacts to give off Phosphine.
Phostoxin comes in 2 forms, tablets and pellets. The tablets are 4/5 of an inch in diameter and 1/5 of an inch thick. and after decomposition takes place, one gram of hydrogen phosphide is released. The pellets are spherical in shape and 3/8 of an inch in diameter. Upon complete decomposition, they release 0.2 gram of hydrogen phosphide. Phostoxin tablets are placed in aluminum flasks containing 1660 pellets each. As long as the containers are kept sealed, their active life is indefinite. However, they should be stored in a dry, cool place, and kept out of the reach of people other than trained personnel.
Almost any dry commodity can be fumigated with Phostoxin, if placed under gaslight tarps or placed in a gaslight warehouse. Packaged commodities can be fumigated without opening, provided the packing is such that it is gas permeable Phostoxin is not a space fumigant. The generation of the gas is slow and as the gas is dissipated more gas is generated and toxic levels will remain. Therefore it is an excellent fumigant for flat storage and box car fumitation.
Hydrogen phosphide reacts with copper and copper compounds. Since many structures contain electrical wires, switches, and motors containing copper, precautions should be taken where fumigating within an enclosed structure to protect these items.
Phostoxin is effective against all forms of insect life, including adult, egg, larvae and pupa. All the insects that infest stored products, such as the orders Coleoptera and Lepidoptera can be controlled.
Dosage rates of Phostoxin depends upon the tightness of the building or the tarps, the pests to be controlled and the temperature of the commodity to be fumigated. When fumigating products stored in bulk, or silos, the dosage is calculated per ton or per 1,000 bushels. When fumigating packed materials or commodities under tarps, the dosage is calculated on the basis of volume. In large steel silos or concrete bins, the dosage will be from 60 to 150 tablets per 1,000 bushels, again dependent upon type of pest, temperature and tightness of area fumigated. Loose grain fumigated under tarps, use 90 to 180 tablets per 1,000 bushels, or when using pellets, 270 to 540 pellets per 1,000 bushels.
When fumigating packed or bagged commodities under tarps, use 20 to 30 tablets per 1,000 cubic feet, or 120 to 225 pellets per 1,000 cubic feet. Structural fumigation, such as flour mills and warehouses, use 20 to 30 tablets per 1,000 cubic feet, or 100 to 150 pellets per 1,000 cubic feet. Tobacco should not be fumigated with more than 20 to 40 tablets per 1,000 cubic feet.
The exposure time depends upon the temperature inside the commodity, the humidity, the type of commodity and the type of insect to be controlled. An approximate exposure time would be:
Very dry commodities such as grain under 10% moisture will require more exposure time. At lower temperatures. when fumigating for control of some of the resistant species of insect, such as rice weevil, maize weevil and grain weevil the exposure time may have to be extended up to 10 days or more. All mites are difficult to control by fumigation, therefore mite infested grain should be left under fumigation up to 10 days. For use of automatic dispensing equipment to be used in charging of silo bins, one should refer to manufacturer's bulletins.
Figure 3. Fumiscope
The Fumiscope is a portable instrument which will quantitatively measure the concentration of gases and vapors in air (Figure 3). The instrument is calibrated for methyl bromide and will indicate directly the concentration of methyl bromide in dry air to an accuracy of 5 percent in concentration ranges from 0 to 100 ounces of methyl bromide per 1000 cubic feet of dry air.
The Fumiscope uses a thermal conductivity cell to compare the thermal conductivity of a mixture of methyl bromide and dry air to that of pure dry air. This difference is converted into an electric current and is displayed on the meter. The Fumiscope contains a power supply for the operation of the cell and meter which operates on 115V ac. The Fumiscope also contains an electric pump and a gas flow rate meter so that air samples may be drawn through the thermal conductivity cell. The flow rate can be adjusted to a constant value regardless of the length or size of sampling tube by the flow adjust knob. A gas drying tube filled with an indicating dessicant is also included in the gas train for use or when extreme accuracy at low concentrations is required.
The Fumiscope being a portable instrument, no installation other than a level place to set the instrument and a source of 115 volt ac power is required.
The Fumiscope is complete in one cabinet and requires no other auxiliary equipment. The various panel controls, etc., are listed:
|Inlet - This hose connector is the gas inlet for the instrument and the sampling tubes may be connected to it directly or through the drying tube when it is required.|
|Drying Tubes—This glass drying tube contains a reversible indicating dessicant (Dririte). When the color of the Dririte is blue it is ready for use. When the color of all the Dririte in the tube becomes pink it is spent and must be regenerated. (See below for instructions and notes on use of drying tube.) The drying tube, when used is inserted in the gas sampling line between the sampling tube and the inlet connection. Indicating "Dririte" is made by the W. A. Hammon Dririte Company, Xenia. Ohio and is available from laboratory supply houses. Other drying agents may be used but some of them will absorb the methyl bromide as well as the moisture and thus will not give true readings. Silica gel as a drying agent should not be used for this reason.|
|Flow Rate Meter - This indicates the gas flow rate in cubic feet per hour and serves to indicate the flow of gas through the instrument so that it can be held constant regardless of minor flow resistances in the supply tuba. A flow rate of l cubic foot/hour is standard for this instrument.|
|If the meter pointer seems to be unstable and tend to wander over a short time period (seconds) the flow rate may be reduced below the 1 SCFH level for zeroing and measuring and then increased again to purge the sample lines.|
|Flow Rate Adjustment—This knob controls the flow rate by adjusting the pump. The flow rate may be increased by fuming the knob counterclockwise. If this knob is turned too far CCW the pump will cease to operate properly and a great deal of noise will result. If the pump ceases to operate properly turn the knob all the way clockwise and then back it off to obtain the proper flow. If this does not comet the problem the pump may be clogged with dirt or some of the internal tube connections may have come loose.|
|Meter—The sensitive meter indicates the concentration of methyl bromide in air. Due to the resistance of the measuring circuit the meter movement is highly damped and will frequently require slight tapping of the plastic cover to secure the proper reading.|
|Model E-2: This switch changes the sensitivity of the Fumiscope so that the meter scale will read the concentration of either methyl bromide or Vikane directly from 0 to 100 ounces per 1000 cubic feet. Since the Fumiscope is twice as sensitive when the switch is in the Vikane position it may be used to read methyl bromide concentrations from 0 to 50 ounces. In effect this provides an expanded scale for measuring the lower concentrations of methyl bromide.|
|The proper use of a drying tube will be almost essential with the switch on the Vikane scale due to the sensitivity of the instrument being increased for moisture as well as methyl bromide and Vikane.|
|Model E-200: This switch allows methyl bromide to be measured in concentrations as high as 200 ounces per 1000 cubic feet as well as the standard l00 ounce range.|
|It has been found that this model is well suited for monitoring the useful concentrations of carboxide. On the 0 to 100 ounce scale one can read carboxide concentrations from 0 to 200 ounces and from 0 to 400 ounces with the switch on the 200-ounce scale. Thus if the range switch was on the 200 ounce scale and you read 120 ounces on the meter scale you would have 240 ounces of carboxide.|
Zero Adjustment Knob—The meter needle may be brought to zero as a pure air sample is being drawn through the instrument.
Line Switches —Separate line switches on both the pump and meter have been provided so that either may be operated separately as the occasion demands.
Fuse—The fuse is in the 115V ac. Replacement fuses are Little Fuse or Buss No. 3AG-1 /2 amp.
Exhaust—A tube connection is provided at the top of the flow meter so that the exhaust gas from the instrument may be disposed of when the instrument is used in confined spaces. As the gas is exhausted at only l to 2 cubic feet per hour connections to this outlet should not be necessary in reasonably well ventilated areas.
Both line switches are turned on. After a warm-up period of 5 minutes, (15 minutes, if drying tubes are used), with the gas flow rate adjusted to 1 cubic foot per hour, the meter needle is set on zero. Several further adjustments within a few minutes may be necessary to secure a stable zero reading (especially when a drying tube is used). The instrument is now standardized and ready to measure the gas concentration when it is admitted to the area under fumigation.
Connect each sample tube from the area under fumigation in succession and mark the maximum reading obtained. Check the zero setting between each sample reading by letting the pump draw ambient air the cell so as to make the pointer come back to zero. If the pointer does not come back to zero after a minute or so reset it to zero before taking the next sample reading and add or subtract the small difference from zero that existed from the previous sample reading. Frequently the zero setting will not have to be changed between sample readings.
Further zero adjustments should not be necessary if the drying tube is used, and should not be necessary without it if there is not a great change in humidity in the area under fumigation, with respect to the humidity of the ambient air used to zero the meter.
After the instrument has been used to measure methyl bromide concentrations the gas system should be purged of all residual methyl bromide by allowing the pump to draw clean air through the instrument for several minutes.
Drying Tubes—If the drying tubes are to be used they must be changed as frequently as all of the dessicant becomes spent, (turns from blue to pink) as a spent drying tube is worse than none at all. When these tubes are refilled with fresh Dririte, that which is emptied should be saved in a bottle and regenerated when convenient. This will result in considerable saving of Dririte. Dririte is recommended since some of the other dessicants that are available will absorb methyl bromide as well as moisture and thus contribute to erratic readings.
Regeneration of Dririte—Place spent Dririte in a shallow dish or pan and heat in an oven to 300 to 400oF for 20 or 30 minutes and return to bottle containing fresh Dririte while still slightly warm. The Dririte may be dried while still in the tubes in the oven at the lower temperature for 30 to 40 minutes (remove rubber stoppers). The drying tubes should be kept closed when not in use.
The Halide Detector consists of a propane torch in which the flame passes over a copper cone, causing the name to change color in the presence of gas vapors in the halogen family of gases (Figure 4). It is primarily used in structural fumigations to check for leaks during fumigation period, and to detect the presence of gas when aerating the structure. It has great value in performing a thorough and safe fumigation when using methyl bromide since the varying changes in color has been tabulated to show the amount of methyl bromide remaining, especially in the lower ranges.
Figure 4. Halide Detector
Open the valve on propane cylinder, light the torch, and after the reaction plate becomes red hot, adjust the flame to a fine steady point where the top of name just touches the reaction plate. It will remain red. Using the pick-up hose, pass the end of this hose close to the areas you wish to check, and note the change in color of the flame. It is important to remember that above the concentrations shown on Table 14, the flame could begin to smoke and become extinguished. At night the flame will have a bluish cast, but will still react, and can be easily read. Table 14 indicates the amounts of methyl bromide in relation to color of the flame. Remember to keep the flame away from combustible materials.
|Cannot zero meter pointer with knob.||If the meter will not zero after clean, dry air has been pumped through the instrument for several minutes, the sensitive filaments in the measuring cell are damaged and must be replaced. This damage is usually caused by water being drawn into the cell or corrosive or high molecular weight vapors in the sample stream being burned on the hot filaments.|
|Pointer wanders about the meter scale sometimes, cannot repeat readings always.||Sometimes a lower flow rate will improve or eliminate this problem. If the readings are good one time and way off the next there may be a loose electrical connection inside the case.|
|Pump does not produce enough flow or becomes noisy.||See section on Flow Adjust for a better understanding of the pump. Check sample tubes for restrictions or if there is no flow but pump does buzz one of the connections inside the case may have become broken. Remove panel and replace tube.|
|Readings are not as high as you might think they should be.||Check for leaks in sample tubing and connections. Connections held together with masking tape almost always leak. Pinch off sample tube and if the flow meter ball does not fall to the bottom there must be a leak.|
|When sample is being measured pointer goes up rapidly and then rises several more ounces over a period of 5 minutes. When the tube is disconnected the pointer falls rapidly to 5 or so ounces and then falls the remainder over a period of 5 minutes or so.||There is higher humidity in the area under fumigation than the ambient air. Either use a drying tube or correct the readings fro this difference by subtraction.|
The following tabulation gives the approximate methyl bromide concentration associated with color intensity in the flame of a Halide Leak Detector.
Although Vikane is rapidly cleared from a building under normal conditions, to assure returning occupants there will be no hazardous residue remaining, the Davis Detector Kit should be used (Figure 5). Results of studies have led to the conclusion that concentrations of Vikane should be reduced to at least 10 Parts per million before allowing reoccupancy. This kit is a small electric furnace that combusts Vikane to gases that can be measured by a change in color in the sampling tube. Directions accompany the kit and should be closely followed to obtain the best results.
Figure 5. Davis Detector
A simple squeeze bulb apparatus is available for measuring concentrations of Phosphine. This equipment is used to draw pre-measured quantities of atmosphere through detection tubes which initiate a color change to indicate the gas concentration parts per million, (PPM). Two types of tubes are available. One type will detect Phosphine up to 1,000 PPM, with graduations of 100 PPM. This tube is used to determine the concentration during different time periods of a fumigation. The other type of tube can measure presence of gas to 10 PPM with graduations of 0.1, 0.5, 1.0, 2.0, 5.0, 7.5 and 10 PPM. This type is usually employed as a safety device for determining presence of gas at very low concentrations. The threshold limits for Phosphine is covered in Section on Toxicological Consideration.
Two types of fans can be used to circulate fumigant vapors in a structure. One is of the axial type, and the other is the squirrel cage type (Figure 6). Axial type fans will move more air than squirrel cage blowers, since the amount of air moved is controlled by the length ant pitch of blades. Therefore, less current is drawn by the axial type for proportionate results. However, they are bulky, and difficult to transport and care for. The small squirrel cage type blowers are excellent for continuous circulation. Wherever the house current will allow it, without blowing fuses, larger fans of the squirrel cage type, operating at a higher RPM can be used to establish equilibrium. It has been established that without forced circulation there will be a rapid flow of gas to the lower portions of a structure immediately upon introduction of the fumigant. In fact. if the bottom seal is poor, the rate of loss would be greater than the upward dispersal of the vapors. It therefore becomes necessary to use forced circulation to obtain good diffusion of the fumigant with the atmosphere of the fumigated space. By use of forced circulation, the gas will be evenly distributed, resulting in an earlier equilibrium (equal mixing of the gas and atmosphere at all levels). It is suggested that a fan of larger capacity, equipped with a timer, be used for no less than one hour after introduction of fumigant, and smaller tans with a capacity of 300 to 400 cubic feet per minute,be placed in several locations to maintain continuous circulation.
Figure 6. Squirrel Cage Fan
Some state laws state that entrances shall be locked, barricaded. or otherwise secured against reentry. This means that to leave any fumigation in such a condition that any person could enter constitutes a violation. Many localities have ordinances requiring special locks. Some require a guard. The types of fumigations where special locks are required. and the times during the fumigation when a guard is required vary. It is the opinion of this writer that a literal interpretation of the (otherwise secured) Act would mean that any fumigation that can be entered by any means is performed in violation, whether special locking devices are used or not.
Figure 7. Pan Lock, Clam Shell Lock
At present there are 3 types of locking device in use. The most widely used is the "pan lock" (Figure 7). This is similar to a baking pan with holes in the bottom through which a small chair is passed. The device is placed over the door knob or handle, and the chain is then wrapped around the knob or handle, passed through the holes and secured with a padlock. The second is a clam shell like device which opens up to slip over the door knob, then closes and locks (Figure 7). The third is a lock plug that is placed into the keyhole, locked with a special key, thereby closing the keyhole. All of these merely prevent a person from inserting a key into the lock for the purpose of unlocking the door. There is no foolproof method as yet to completely barricade or otherwise secure a building against reentry without the use of a guard.
The safest means of releasing fumigants is to release them from outside the structure by means of tubing attached to cylinder, and leading into the fumigated space. Due to the low boiling point of Vikane, no special vaporizing device is needed, therefore the tubing can lead directly from the cylinder to the area under fumigation. Vikane should be released through 1/4-inch OD polyethylene, polypropylene or nylon tubing (Figure 8). No tubing larger than this should be used because the rate of flow would be too great for good distribution. Three to five pounds per minute is the best rate of release. The release tube should be positioned so as not to allow the possible frosting of tube to drip onto household effects.
Figure 8. Releasing Tube
Methyl bromide is usually passed through a heat exchanger in order to vaporize it. The size of the tube leading from the cylinder to heat exchanger should be no larger than 1/4 inch. This prevents too rapid release sate and resultant overloading of heat exchanger. After the fumigant passes through the heat exchanger, it should never be restricted and forced to pass through any opening smaller than the one previously passed through. A good rate of vaporization can be maintained by keeping the tube leading from the heat exchanger to the fumigated space no smeller then 1/2 inch in diameter, 3/4 inch would be better. If restricted, condensation can occur. Methyl bromide should never be released directly onto floors, walls or household effects.
The dosage of fumigants is usually figured on the basis of the number of cubic feet in the space to be fumigated and expressed in thousands of cubic feet. The prices charged for fumigations is also based on this system. Therefore, it is necessary to understand how to calculate the cubic content in any space to be fumigated. In most structures, it can be simply stated that this can be accomplished by multiplying the length by the width, and then multiplying the result by the height. However, one must have some knowledge of how best to do this since most buildings are irregular in shape and have peaked or gabled roofs, and the height used will have to be the average height.
In the following diagram (Figure 9), which is a simple structure with no additions or wings to consider, the only thing one must understand is the height of this building that will be used is one-half of the height of the attic area added to the height from ground to roof cave. In this case this makes the average height one-half of 6, which is 3, added to the wall height of 10. This gives us the average height. Therefore, the cubic content of this structure would be 40' (length) x 20' (width) x 13' (average height), which gives us 10,400 cubic feet. Now this means that if we are to use a dosage of 3 pounds of fumigant per one thousand cubic feet, we would multiply 10 x 3, since we are using units of thousands for calculating dosage. The answer would be 30 pounds plus an additional 1-1/2 pounds for the extra 400 cubic feet.
Figure 9. Diagramatic Sketch of House with no Additional Wings
The following diagram (Figure 10) is a little more complicated. Note that a lean-to type room and a sub-area has been added to the main structure. The same procedure as before is followed, but it is easier to understand if calculated in sections As indicated by the encircled numbers, there are 5 sections. The first one being the number of cubic feet in the main section, less the attic and sub-area. The second one being the main section of lean-to, less the attic and sub-area. The third one being the attic area of main portion of structure. The fourth one being the attic area of lean-to, and the fifth the sub-area of main portion of house plus the sub-area of lean-to.
Figure 10. Diagramatic Sketch of House with Additional Wings and Sub-area
To obtain the total cubic content of this structure, cube each of the 5 sections separately, then add them together.
|Section No.1:||40' length x 30' width = 1,200 square feet.
1,200 x height of 8' = 9,600 cubic feet.
|Section No.2:||30' x 10' = 300 square feet.
300 square feet x height of wall - 6' = 1,800 cubic feet.
|Section No.3:||40' x 30' = 1,200 square feet.
1,200 x 1/2 of height of attic which would be 3' = 3,600 cubic feet.
|Section No.4:||30' x 10' = 300 square feet.
300 x 1/2 of the attic height of 1 = 300 cubic feet.
|Section No.5:|| 40' x 30' = 1,200 square feet + 30' x 10' which is: 300 square feet = 1,500 square feet.
1,500 x sub-area height of 2' = 3,000 cubic feet.
Total number of cubic feet would be:
At the rate of 2 pounds per thousand cubic feet, the dosage is 2 x 18 units of 1,000 which equals 36 pounds plus approximately 1 pound for the additional 300 cubic feet or, 37 pounds of fumigant.
The quality of the seal is probably the single most important phase of any structural fumigation. Some stucco and masonry buildings can be sealed by covering all exterior openings with laminated paper and masking tape, providing the exterior walls are not too porous, and the roof covering is gaslight. Most composition shingle roofs, especially those placed over wood shingles are not gaslight. Brick, and most masonry block walls are too porous to effectively confine the fumigant by the paper and tape method. Since all fumigants must have rapid distribution (by means of forced circulation) upon introduction, tape and paper seals are less desirable than covering the entire building with gaslight tarpaulins because they lessen the probability of good circulation.
The 3 most important factors in obtaining a good seal on a tarp fumigation are:
Detailed information on fumigation procedure will be kept essentially basic in this manual, since there are several excellent manuals that cover this subject. A structure that is to be fumigated should be closely inspected to determine:
As previously mentioned, buildings with stucco exterior walls in good condition, gaslight roof, and without excessive wood trim, can be sealed by the tape and paper type of seal. This is best done by covering all exterior openings (windows, doors, vents) with gaslight laminated paper that is secured with 1 inch wide masking tape. It may be necessary to staple the paper in place before taping. The paper should be cut to fit the openings as near as possible, but should extend far enough to cover all wood trim. In other words, the paper should be taped to the stucco on all sides of these openings and not to the trim.
The next step is to seal the vent pipes that extend through the roof. These are usually heater vents. It is not always necessary to seal the plumbing vents, since some of them will have a water seal at the base, and others will not allow gas to enter them anyway. An easy way to seal these vents is to cover them with polyethylene film at least 4 mil in thickness and secure with masking tape or small soft line.
Situations where tarp fumigation is necessary would include buildings with wood siding' shingle or any other type of roof covering that in the fumigator's opinion would not be gaslight. Also included are stucco buildings with tile roofs that have wood trim, and buildings with porous masonry block, brick, or stucco walls that are in poor condition. Experience has proven that the most acceptable type of tarp material used is 7 ounce, vinyl-coated nylon. These tarps are made for the fumigation industry, and all fumigators have their own particular sizes that they prefer. About the maximum size that a man can carry up a ladder is 40' by 60'. Every fumigator should have some tarps of smaller dimension in order to work them around obstructions such as antenna, power lines or other structures that might be fastened to the building.
Before placing tarps in position, measurements should be taken to ensure that the best possible use is made of the tarps, thereby eliminating all unnecessary joining together of several small tarps. Since these tarps are joined together (which could be points of leakage), the number of seams should be kept at a minimum. Some antennae can be left in place and worked around, but it is necessary to remove some of them. All sharp corners should be padded by stapling rug pads or other protective material. After fitting the tarps to the building, with at least 2 to 3 feet at the bottom edge resting on the ground for the purpose of sealing, the edges should be joined together by rolling tightly for 3 or 4 turns, and secured with spring clamps spaced no farther apart than 12 to 18 inches. Where stress will occur, they may be placed closer.
There are several methods of sealing the tarps at the ground surface. Probably the best method would be to trench the soil around the building, piece the bottom edge in trench, then back fill with soil. This cannot always be accomplished, since some buildings have valuable plantings next to the foundation and the owner will not allow trenching. The next best method would be to haul in damp sand, and after leveling the surface, spread the sand on bottom edge. The most widely used method is by using sand snakes. These are made up of bags that are from 4 to 6 feet in length, approximately 5 inches in diameter, filled with sand and tied at the ends. These are pieced on bottom edges of tarps with ends overlapping. The important thing to remember with this method is to have the ground leveled so the snakes will fit snugly to the surface. Some fumigators will double snake. This means at every joint, an extra snake will be pieced so as to overlap the joints. Wherever the snakes go over walks, steps, stone outcroppings or uneven ground, extra soil can be pieced to level these areas.
The foregoing is a general description of the 2 types of seals, but is not necessarily the sequence of the steps that should be followed to accomplish a fumigation. These 8 steps should ensure a safe fumigation.
A suggested sequence would be:
After completing the job and injecting the fumigant, a check should be made with a leak detection device. All litter should be cleaned up and removed from the premises and proper danger signs posted.
Figure 11. Sign Should Be Posted
Around the Exterior of the
Building When Fumigating
A knowledge of the chemical properties of fumigants is essential if one is to thoroughly understand aeration procedure. Fumigants with a high boiling point are more difficult to dissipate from a structure than those with a low boiling point. Terminal concentrations of fumigant remaining at the end of the exposure period will vary according to amount injected, length of exposure, and the degree of confinement. The usual ranges of methyl bromide will vary from 4 to 16 ounces per 1,000 cubic feet, or from 1,000 parts per million to 4,000 Parts per million. The amount of Vikane remaining would usually be in the range of from 2 to 8 ounces, or from 500 to 2,000 parts per million. Reoccupancy of the structure should not be allowed until methyl bromide residues have been reduced to at least 20 parts per million, and Vikane residues have been reduced to at least 10 parts per million.
If a check with a Fumiscope is made at the end of the exposure period, it will aid the fumigator to properly plan his aeration. The important thing to remember is to get as many windows and doors open as possible on opposite sides of structure in order to create cross flow of air This should be done in stages by 2 men wearing approved gas masks, and opening a few windows at a time. Do not attempt to remain in the building long enough to open all windows and doors. The building should then be allowed to stand for awhile before entering to complete the opening of windows. There is usually some work that can be done while this is occurring. No crewmen should be allowed to work or stand in the immediate vicinity of open windows until a considerable amount of aeration has occurred. When a check with a gas detection device shows that the fumigant concentration has been reduced to a level low enough to allow the fumigator to enter without a mask, a thorough check can be made with a gas detector in closed areas, such as, clothes closets, cabinets, furnace wells, and basements to ensure that no transient residues remain. At this time, the utility gas service can be restored and pilots lighted. Usually the fans used in circulating the fumigant during the exposure period will be of help in moving the gas from the larger portions of the building. Since low temperatures slow the diffusion of a fumigant, it will also slow the aeration. Under difficult condititions it may become necessary to employ larger exhaust fans to facilitate the ventilation.
As mentioned before, certain fumigants, due to their chemical and physical properties, are more difficult to clear out of a building than others. Vikane, with its low boiling point and high vapor pressure, possesses properties that are favorable to rapid aeration. Another important factor to consider in aeration is the absorption of the fumigant by certain materials and components in a structure. The usual items in a household do not play a large part in absorption. However, fumigants that are least likely to be absorbed or react with the principal components of a building will penetrate more rapidly, and in the early stages of exposure will be more apt to diffuse into the areas of infestation.
Wood such as fir, which is the most widely used in the framework of residential buildings, has pore space that is so small, they can only be detected with a microscope. Yet all of this pore space will be exposed to a fumigant having no reactive qualities or affinity for wood, and will be desorbed without difficulty. The desorption process of methyl bromide is considerably slower than that of Vikane. However, it is considered to be a fumigant with excellent penetrating powers and can be safely aerated from a building with proper aeration procedure. Care should be taken to leave a few windows open, although a detector shows no presence of fumigant. The residues of fumigant that remain in materials not completely desorbed, can build up in the living quarters after the building is completely closed again.
Bulletin 132-47. Dow Chemical Co. How to Fumigate Buildings with Dow Methyl Bromide.
Fumigation Training Manual. Young. Pest Control Operators of California, Inc.
Training Outline for Safe Practices in Handling and Using Phostoxin Fumigant. Phostoxin Sales. Inc.
Operating Inductions for Fumiscope. Robert K. Hassler Co., P.O. Box 177, Altadena, California.
Toxicological Considerations of Fumigants. Torkelson, Hoyle and Rowe, Biochemical Research Laboratory, Dow Chemical Co., Midland, Michigan.