Miller Magazine Issue: 116 August 2019

84 ARTICLE MILLER / AUGUST 2019 Aeration and release of fumigant residues When fumigation is over, the release of the fumigant is an important procedure. This pro- cedure involves, where possible, active aera- tion. Most grain silos are equipped with aera- tion system. Such aeration systems operate within a range of airflow 3 to 12 (m3/h)/tonne (Annis and Graver, 1990). It is important to en- sure that such airflow is available and it can be used to remove the fumigant. With airflow in pressure system, during aeration, the exhaust system should convey the air directly to the at- mosphere. In suction systems (airflow from top to bottom of the silo), gas contaminated air is conveyed to the bottom of the silo, Therefore, care should be taken to avoid presence of workers at air exhaust point, To avoid workers respiration of the fumigant contaminated air, warning signals that the fumigant is released to the atmosphere should be placed in visi- ble sites (Annis and Graver, 1990). To ensure complete release of the fumigant, an intermit- tent aeration procedure should be applied. In this process, after an initial two hour aeration, several hours of pause will enable desorption of the gas that was sorbed (absorbed) by the commodity into the interstitial airspace of the grain bulk. Such procedure can be applied for phosphine with two cycles of intermittent aer- ation and for methyl bromide several more cy- cles would be necessary. For facilities that are not equipped with aer- ation system, the solution is to turn the grain through the conveyor chains and elevators. This process causes in each passage the grain to shrink (and break), facts that are far less desirable than aeration for releasing the fumigant. In some cases for grain stored in si- los without aeration systems, after fumigating with phosphine gas, a simple opening of the top silo hatch is considered as aeration. This method has its own disadvantages of spread- ing uncontrolled phosphine concentrations around the silo posing a risk to workers safety. Following a fumigation under tarpaulin, the conventional method is to uncover the stack of grain and release the fumigant to the ware- house or enclosure where the commodity is stored. In such case extreme care should be taken by the fumigator to use appropriate RPE during the uncovering the tarpaulin. In addi- tion, workers should be warned not to enter the premises where the fumigant is released. The fumigator should check the gas concen- tration using the personal gas detector to en- sure that the concentrations are below the permissible limit for entering the premises. When fumigating with solid phosphine (pills/ tablets/blankets/plates), the fumigator must collect and deactivate the remaining phos- phide dust. During deactivation, the fumigator must be protected with PPE which includes a mask, goggles (or whole-face mask), gloves, working shoes. Fumigants are among the most toxicant products of all pesticides. One should act with care and attention while in any kind of opera- tion with them. Most fumigants are odorless, colorless and cannot be detected unless using a specific measuring device. Bibliography Annis, P. C., & Graver, J. V. S. (1990). Suggested recommendations for the fumigation of grain in the ASEAN region Bond, E. J., & Monro, H. A. U. (1984). Manual of fumigation for insect control (Vol. 54). Rome: FAO. Graver, J. V. S. (2004). Guide to fumigation un- der gas-proof sheets. Food and Agriculture Or- ganization of the United Nations. Navarro S. (1998) Pressure tests for gaseous ap- plications in sealed storages: Theory and practice. p. 385-390 (Vol. I) (In) Proc. 7th Int. wkg. Conf. Stored-Product Protection, (Eds. Zuxun, J., Quan, L., Yongsheng, L., Xianchang, T., and Lianghua, G.) 14-19 October Beijing China, Sichuan Publish- ing House of Science and Technology, Chengdu, Sichuan Province. Walter, V. E., Gold, R. E., & Hamman, P. J. (1999). Structural and Commodity Fumigation. Texas Agricultural Extension Service, Texas A & M University System. Wikipedia (2019a) https://en.wikipedia.org/wiki/ Respirator_assigned_protection_factors. Last ed- ited on 15 March 2019 Wikipedia (2017) https://en.wikipedia.org/wiki/ Powered_air-purifying_respirator last edited on 7 April 2017 Wikipedia (2019b) https://en.wikipedia.org/wiki/ Self-contained_breathing_apparatus last edited on 8 June 2019.