New fumigation technique

by Teresa Acklin
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Mobile computerized unit generates gas for silo and space fumigation.

By Jeremiah B. Sullivan

   Hydrogen phosphide gas (phosphine) has been used for more than 50 years as a fumigant to control infestation in stored products. One of its main advantages is that the amount used for fumigation when mixed with air results in a density slightly heavier than air (1.0005). As a result, this fumigant/air mixture is an excellent penetrator and equilibrates within a structure or commodity very rapidly.

   Over the years, metal phosphide products, including tablets and pellets, have been developed to deliver phosphine for fumigation. All of the metal phosphide products are extremely useful and are capable of obtaining a complete elimination of the infestation if used properly and if proper deactivation techniques are employed following fumigation.

   As good as these products are, there are some disadvantages in the application. The product has to be placed inside a structure, probed into grain or added to the grain stream during the filling of a bin, silo or flat storage. Also, these products are effective only under certain temperature and humidity conditions.

   Respiratory equipment is required to enter the facility to recharge with additional gas, repair a leak or aerate. The products also must be applied to avoid accumulations leading to large concentrations because 1.79% (17,900 ppm) can ignite if an ignition source is present. In fact, the products themselves can be the ignition source as the reaction between water and metal phosphides is exothermic (produces heat). Recovery of spent residues and deactivation of the spent product also are necessary.

      Computerized Phosphine Generator.

   During the past few years, a new fumigation method has been under development by Franziskus Horn, owner of Fosfoquim S.A., Santiago, Chile. The eventual product of his research, known today as the Horn Generator, was included in the “What's New?” program at the recent Grain Elevator and Processing Society annual conference.

   While working on the generator, Dr. Horn also was developing a new granular magnesium phosphide preparation at Degesch de Chile, Ltda., a subsidiary company of Degesch GmbH, Frankfurt, Germany. This product produces one gram of hydrogen phosphide gas from two grams of the granular magnesium phosphide.

   In the new fumigation system, the granular phosphide product is placed in the generator's reaction chamber, and the hydrogen phosphide gas developed is mixed with air and a small amount of carbon dioxide. Gas generation is computer controlled and is operated with four buttons — start, stop, restart and wash — on the computer portion.

   The various functions are also programmed so that any malfunction will result in an audio alarm. In case of malfunction, the unit will close down and be flushed with carbon dioxide for total safety. The only other product that is produced by the generator is the magnesium carbonate solution that results from the wash cycle.

   The generator, when used for fumigation purposes, will produce on an hourly basis hydrogen phosphide gas that is equivalent to 5,000 tablets. In actuality, more gas is produced from the granular magnesium phosphide as more complete reaction occurs in the Horn Generator.

   The success in producing a fumigant gas mixture with this new equipment also required development of new application techniques. First, a new method was developed for silos, tanks, bins, flat houses, etc.

   As seen in Figure 1, the procedure involves placing 5-centimeter PVC piping in the bottom of the structure to be fumigated and a gas test line on top of the grain surface. The gas mixture is introduced via a blower into the bottom of the structure. Once gas is detected above the surface of the grain, the generator and blower are turned off and the application is completed, usually in one hour or less.

   A similar method was developed for flour mills, as seen in Figure 2. The same 5-cm PVC piping is permanently installed into the bottom of the mill with other piping going to each floor and manifolded on each floor.

   The generator is connected to the inlet pipe and a pipe from the mill so that internal air from the mill is blown through the generator. The air is mixed with the hydrogen phosphide/carbon dioxide gas mixture and then is introduced into the mill, a procedure that does not cause any pressure changes in the mill. A facility of approximately 15,000 cubic meters can be placed totally under fumigation using two generators in one hour or less.

   Because the Horn Generator produces gas as soon as it is started, fumigation concentrations are developed very rapidly when compared with the gas produced from metal phosphide formulations. This difference is clearly demonstrated in the chart.

   The Horn Generator system, which can also be used to aid in aerating the commodity following fumigation, has several major advantages. Application is made totally from outside the facility; fumigation levels are attained in faster time; if leakage occurs, repairs can be made and more gas can be introduced without entering the facility; and, following completion of the fumigation, there is no residual dust or spent product to be gathered and deactivated. In addition, temperature and humidity are no longer a concern, and much less labor is required for the fumigation and aeration.

   Another feature is mobility, as the system can be assembled in either a van or the bed of a pickup truck. The generator itself measures 78 cm by 78 cm by 108 cm and weighs about 135 kilograms. The mobile system comprises the Horn Generator along with a water tank, cylinder of carbon dioxide and an electrical generator.

   The cost to fumigate with the Horn Generator is similar to that of fumigation with metal phosphide preparations. The unit will be made available through Degesch distributors when the magnesium phosphide product is purchased.

   The initial plan is to charge a small additional fee for each kilogram of the magnesium phosphide product rather than to sell the Horn Generator. The unit will by no means replace tablets, pellets or packaged products in certain types of fumigation.

   Jeremiah B. Sullivan is president of Sullivan & Associates, a consulting company involved with marketing, training programs and legal and regulatory issues relating to fumigants. Dr. Sullivan is a member of the European Society of Toxicologists and the American College of Toxicology and is adjunct professor of chemistry at James Madison University, Harrisonburg, Virginia, U.S.