Behaviour of fumigants during vacuum fumigation. I. - Penetration of methyl bromide into boxes of dates

The penetration of fumigants into packages during treatment by various methods employing reduced pressures, as well as at atmospheric pressure, can be studied by measuring gas concentrations. A ‘penetration factor’ is defined, which allows comparison of the effectiveness of penetration in different methods of treatment. Preliminary laboratory tests with methyl bromide have been carried out, mainly on boxes containing tightly compressed dates. The ‘sustained‐vacuum’ method, as normally used, gave higher penetration factors at the centres of boxes of dates in three hours than the method in which an air‐fumigant mixture is introduced to the evacuated chamber. Very low penetration factors were obtained in this period in tests at atmospheric pressure. It was found that, after a period of fumigation at reduced pressure, release of the vacuum produced very high concentrations at the centres of boxes. It is suggested that utilization of this effect in a modified vacuum‐fumigation procedure should result in increased efficiency. The ‘air‐washing’ technique for the removal of fumigant at the end of a treatment has also been examined.