Both field gastightness trials before fumigation and phosphine
recirculation fumigation in grain bulks covered with the plastic
sheet of PVC were carried out in three horizontal bins of Deqing State Grain Depot.The results of gastight test indicated that t 1/2 (decline half time) of pressure from -500 Pa to -250 Pa for three horizontal bins were 54,48 and 46s respectively.They were higher than 40s of t 1/2 which was Chinese recommended standard for new horizontal bin. At gastight conditions the exposure time for average concentration over 0.02mg/L of phosphine were respectively 26,23 and 18 days for the three bins during
recirculation fumigation.The CT values of them were respectively 165.63,134.36 and 109.37 mg·h/L when fumigation trials ended.The declined rates of average concentration of phosphine in three bins were 3.62,4.06 and 5.15%/d.The order of t 1/2 of three bins were the same with that of exposure time over 0.02mg/L ,CT values,and declined rates of concentration of them.The gastightness measurement with pressure test is very important in phosphine fumigation. After the phosphine gas put in grain bulks in the trials funs of circulation run for five or six hours,the gas distribution was well.The ratios of minimum and maximum concentration were above 0.5 at that time when were shorter fourteen or sixteen hours than of the
Recirculation fumigation without seal surface of grain bulks in horizontal bins.The mortality of all stages of Sitophilus oryzae (L.) resistant strain to phosphine, Sitophilus zaemais (M.), Tribolium castaneum (Herbst.),and Rhyzopertha dominica (F.) were 100% after fumigation for four weeks.The trials of three bins got successful fumigation for control stored grain insects.