Winter Fumigations

January 2025 Edition: Winter Fumigations by Curtis Lilleoden

It's January, you are experiencing intolerable pest levels and one of the control options you are considering is fumigation. As a fumigator, a phone call for a wintertime fumigation is met with positive apprehension. On one hand, it’s generally our slower season and the unexpected work is always welcomed. On the other, winter fumigations in the Midwest can be quite challenging.

If you read my article Insect Rate Fumigations from the August 2024 issue, I mentioned, and you may recall:

[Temperature can also cause the gas to behave differently. There are instances, especially with taller buildings, when the range in temperature from within the structure to the temperature outside, can affect how well it will hold gas. Warm buildings in warm weather usually hold gas better than warm buildings in cold weather. The same structure may not hold the fumigant as well in November as it did in July and may require more fumigant to achieve the same results. If a building or structure is not adequately insulated or heated, it may not be suitable to fumigate for insects at all during colder weather.]

When fumigating at lower concentrations for warm-blooded animals such as house mice, buildings do not necessarily need to be heated or at least kept as warm, so it does make some of this easier, but the following principles and practices still hold true and need to be prepared for.

There are many things to consider during a winter fumigation that are not as critical during warmer months. Most structures tend to “loosen up” a bit during cold dry periods generally associated with winter so they will not hold gas quite as well.  Heaters: if your building is heated, any source of heat at or near 752˚ Fahrenheit will need to be turned off. Depending on how well the building is insulated, temperatures can start to drop quickly once the heat has been turned off. Concerns for water pipes and sprinkler systems freezing (and breaking) are real during below-zero weather.

There are also safety concerns for the fumigation crew. Winter weather driving can be quite treacherous. Most fumigations are planned well in advance without knowing what the weather will be over the course of the fumigation. Extra travel time should always be planned for. Once on the job, there is concern for slippery surfaces, frost-bite and hypothermia. Sealing can be very difficult; often spray adhesives need to be used to get tape and other sealing materials to hold. Ice and snow build-up at seal points, particularly along door thresholds and exhaust vents will also create problems with adhesion. If using a lift to seal openings at heights, plan to have the proper equipment to get through the snow, or is it too deep to drive through? Is there a warm enough area to keep and run the gas monitors? Will the gas cylinders need to be warmed up prior to release? These are all things to consider when fumigating in extreme cold.

Unfavorable conditions may also require more labor. Everything seems to take longer to complete in the bitter cold, and winter days being much shorter, puts workers out in the dark for longer periods, which can increase safety risk.  Make sure your crew has the proper dress and footwear for cold weather. Providing hand warmers, and a place to frequently warm back up should also be considered. We know how important it is to watch for heat stress in the summer, we need to also watch for cold stress during the winter.

With all of this to be considered and prepared for, there is still one (and usually the biggest) challenge when dealing with the cold during a fumigation is the stack effect. Warm air is less dense than cold air, thus warm air rises and cold air sinks. (I think most of us know this already.) Insects need to be warm to be active, and they need to be active to effectively fumigate. As we heat the building, the air in it rises. This rising air creates lower pressure at the lower levels, which draws in cold fresh air through openings at ground level. These openings can include doorways, windows, HVAC systems, dock plates, and any pipe penetrations through walls and openings from structural damage and aging.  The hot air in turn leaks out the upper levels through the same openings as well. This natural phenomenon is known as chimney or stack effect.   The more we heat the building, and the greater the difference between warm interior temperatures to cold exterior temperatures, the greater the effect. As this warm air moves up and out of the building, so does our gas, while at the same time it is being diluted by the cold fresh air coming in at lower levels. Maintaining concentrations of fumigant under these conditions can be extremely difficult, if not impossible (or at least practical). The opposite happens in warm months if the interior is much cooler than the exterior temperatures, but this is usually easier for an experienced fumigator to deal with.

This problem is compounded by the size and height of the structure. Quality of the building construction, construction insulation materials and even the HVAC system all contribute to a structure’s “tightness” and its ability to hold a fumigant. All these factors contribute to the half-loss time, which is the way we measure a structures ability to hold the fumigant.

 Lower temperatures and a shorter half loss time will at the very least require more fumigant to achieve success. In most structural fumigations, the cost of the fumigant is the single biggest expense, so increasing the amount of gas needed will add to the cost of the fumigation, sometimes significantly. Thus, some buildings that can be effectively fumigated in the summertime, cannot in the winter.

If you are considering fumigating this winter, consulting with an experienced professional from FSS can help you decide whether it is practical, doable, or not possible. When a winter fumigation is not practical, we will help you find a solution to help get you to more favorable weather in the spring.

Stay warm!