Critical Limits of Sealing for Successful Application of Controlled Atmosphere or Fumigation
S. NAVARRO1* AND J.L. ZETTLER²
¹Dept. of Stored Products, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel [*e-mail: snavarro@vtshlo.netvision.net.il]
²Horticultural Crops Research Laboratory, USDA-ARS, Fresno, CA 93727, USA
Abstract: A fundamental requirement for the successful application of gaseous treatments to control stored-product insects is a well-sealed structure. A flexible fumigation structure of 7.5 m³ capacity marketed as the "GrainPro Cocoon™" that is used for outdoor storage of stacked commodities was used to demonstrate the critical limits of the degree of sealing using the variable pressure test. Time in minutes for the half-life pressure decay was correlated with daily ventilation rates of O₂, CO₂, PH₃ and MB. The ventilation rates were tested using different sizes of cross-section leak areas with orifices of 1.6 mm, 3.2 mm and 6.4 mm i.d. To evaluate the influence of temperature on the rate of gas exchange, the cube was tested when it was under cover by providing shading to minimize the direct solar heating effect, and when it was exposed to direct solar heating. Oxygen infiltration rate for modified atmospheres was 0.5% O₂ day⁻¹ at 5 min half-life pressure decay when the chamber was under shade. For the same level of gastightness, gas loss was 0.8% O₂ day⁻¹ when exposed. CO₂ loss rate was 2% day⁻¹ at 5 min half-life pressure decay when the cube was under shade and 3% day⁻¹ when the cube was exposed. Loss rate of PH₃ from the cube for the shaded conditions was 100 ppm day⁻¹ at a 3-min half-life pressure decay time. A sealing equivalent to 4.5 min half-life pressure decay time was required when exposed. The MB loss rate of 1.0 g m⁻³ day⁻¹ was equivalent to ~ 5 min half-life pressure decay time. At the time tests were carried out with MB, ambient temperature differences were not large enough to show different loss rates between the shaded and the exposed cube.
Key words:
