A new method of ensuring even distribution of a fumigant in flexible fumigation chambers using external fans

A series of commercial fumigations to control narcissus fly larvae in bulbs for export was carried out to determine the effectiveness of a gas distribution method that utilizes external fans positioned outside the chamber. The principle is to generate air motion using the flexibility of the PVC liner. This is done by directing an air-flow along the walls of the liner, thus creating a ripple motion that generates an internal turbulence which mixes the air with the fumigant inside the chamber. With fans placed opposite the corners of the bubble it was possible to divide the airflow along all sides of the bubble wall. Methyl bromide concentrations recorded over the 4-h fumigation period, were compared with previous results obtained when the fumigant was mixed by recirculation. The use of external fans in combination with flexible PVC chambers enabled an even gas distribution to be achieved within the chambers in 1-1.5 h whereas under recirculation, even distribution was not reached during the entire 4-h fumigation period. Post-fumigation mortality data on narcissus fly larvae revealed 100% kill.