Pre-Mix and on-site mixing of fumigants

  • R. F. Ryan VAPORFAZE, , PO Box 4, Sans Souci NSW 2219, Australia. Email:
  • W. P. Shore GasApps Australia Pty Ltd; 6/20 Valediction Rd, Kings Park NSW 2148, Australia


Pre-Mix or On-Site mixing, a common practice with liquid insecticides, has benefits of increased synergy with fumigants. Both Pre-Mix and On-Site mixing have some issues with compatibility (e.g., active ingredient chemical stability; material compatibility; reaction with other ingredients). In addition to its fumigant properties, carbon dioxide (CO2), has a synergistic effect on other fumigants and reduces flammability. The general consensus on the amount of CO2 to improve efficacy is in the range 5%-20%. The early recognition of the benefits of CO2 to overcome the flammability of potential fumigants by Jones (1933), initiated safe and more effective fumigant mixtures: examples are ethylene oxide (12.2 vol%), ethyl formate (14.4 vol%) and propylene oxide (8.3 vol%).

The main advantage of gaseous phosphine (PH3) use is reduced generation time and uniform PH3 distribution in hours not days. Other advantages of gaseous PH3 include accurate metering of PH3 fumigation levels and reduction of Occupational Health and Safety exposure to PH3. Gaseous PH3 in a Pre-Mix with liquid CO2 or mixed On-Site with gaseous CO2 or N2+Air to reduce the PH3 level below Lower Explosive Level of 16,000 ppm. A critical impurity of CO2 when mixing with PH3 is oxygen which must be less than 0.01% to avoid the formation of the polymer, (P2H4CO2)n. Large quantities of PH3 are used to treat grain storage up to 280,000 tonne [CBH, WA] and multiple 30,000 tonne silos at Dalian, China (1.4 Mt facility). Reports indicate synergy with a mixture of propylene oxide (C3H6O), sulfuryl fluoride (SO2F2) and CO2. This mixture is an attractive candidate for a Pre-Mix or On-Site mixing of a non-flammable synergized mixture with reported 100% efficacy for all insect life stages.

Keywords: Fumigant mixtures, Synergised, Non-flammable, On-site mixing.

Section: Fumigation, Modified Atmospheres and Hermetic Storage