Space Spraying: Thermal Fog vs. Cold Fog

Space spraying can be accomplished using one of two forms of fog; thermal fog and cold fog.

Thermal Fog

The insecticide used in thermal fogs is diluted in an oil-based transporting fluid. Hot gas heats this fluid, causing the oil to become vaporized. When the hot vapor exits the machine distributing the pesticide, it hits cooler air, creating a visible, white, dense fog.

There are several advantages to using a thermal fog. The reaction with the cooler air creates a visible cloud, allowing the operator of the machine to ensure thorough placement of the spray. Because the transporting fluid is oil based and not water based, less active ingredient is needed during the treatment, allowing for a lower concentration of exposure for humans dwelling in the region being treated.

However, there are several disadvantages to this treatment. Thermal fog operations are very expensive. An oil-based transporter in very pricey and can also be a fire hazard in the areas in which it is sprayed. Oil can also cause staining and leave heavy odors. It can leave roadways slick and cause possible traffic casualties.

Cold Fog

A cold fog is just another term for a diluted insecticide. There is no transporter fluid used other than the formula used to create the insecticide. There is no heat involved, and spraying is accomplished by using a high pressure nozzle.

The main advantages to cold fogs are that they are cost effective and pose little to know fire hazard. The water-base keeps roadways from becoming slick and is virtually odorless.
There are issues with cold fogs as well. The fact that they are nearly invisible makes them nearly impossible to observe, impacting the homogeny of dispersion. Without an oil-based matrix, the chemical can often evaporate or deactivate before it treats the area thoroughly.

Which to use?

Thermal fogs would be more appropriately used in areas where the pest being treated was a severe endemic. Areas with few roadways would be ideal. It is also a choice to use when the budget for treatment is larger.

Cold fogs are more appropriate in areas where the pest is not an issue that has grown out of control. It is better for areas with high traffic and heavier populations. It is also the better choice when the budget for treatment is small.

Ideally, in areas where there are both rural and urban populations, both treatments should be used together, breaking up the region into a mosaic of treatment types.

This information was collected from data posted by http://www.who.org/.