Keep It Positive, People

Columns - Tech Talk

October 27, 2021

Flies might be an annoying nuisance when you are trying to enjoy a mocha at your local coffee shop. But if your client owns that shop, the health inspector will use terms like “vector of disease” and “food safety risk” to describe these tiny, winged insects. Whether your client operates out of a storefront or a stand-alone food production facility, these little pests are a big issue, regardless of the auditor or inspector.

But what happens when controlling these pests seems impossible? For instance, even though your client has excellent sanitation and a well-maintained exterior envelope, and you may be performing strong pest management techniques, uncontrolled arthropods may be a persistent problem in your facility.Before they drive you mad, consider if the facility simply sucks.

Let me explain! I am not suggesting you get upset about the facility, nor that your facility is necessarily bad. I am suggesting the building’s air pressure may be negative, which means it sucks air (and arthropods) in. By thinking that negative (pressure) sucks, we remember and can help our clients understand what negative air pressure (NP) does. Ultimately, it pulls air in, along with arthropods. That is why we must always consider NP in our control solutions.

WHAT IS NEGATIVE AIR PRESSURE? A sensitive packaging facility once called us to address its flying insect problem. Breezeways, furnace filters covering window screens and multiple monthly exterior applications were a few of the aggressive corrective actions directed by this facility. While this level of program ownership is admirable, to a point, it is also a sign of desperation. They did not trust their provider, which is why they ordered exterior applications every 21 days for a pesticide that has a three- to six-month residual persistence. I empathized with this controlling client because they were at risk of losing a million-dollar account, and their pest management provider was unable to solve the problem.

I was still new to NP, so I needed to do some research. Here is what I learned.

NP is the force that pulls air in like a giant facility-wide vacuum. Small arthropods that are naturally impacted by air movement (e.g., midges, mosquitoes, spiders that use ballooning, etc.), as well as some that are not, can be forced inside. This can cause thousands of pests to unwillingly enter a single window each day and renders traditional control measures ineffective. It does not matter if your client is a food-processing facility, warehouse or coffee house (especially one with a drive-through window); NP is a significant food safety issue.

WHAT ARE THE SIGNS? The most significant sign that points to a NP issue is difficulty entering an exterior door.

When extra force is required to pull an exterior door open an inch before the door becomes free and swings open normally, you may have a NP problem. You also may see an adjacent breezeway door “magically” open and ceiling tiles flutter when you open one exterior door.

If the problem is not so evident, performing the “tissue” test might demonstrate a less forceful NP issue. While a facility’s production lines are running, place a tissue against the outside of a window screen. If the tissue sticks to the screen, then a NP problem exists. I will explain the production importance later.

CAUSES OF NP. When a building is being constructed, its air pressure is neutral, just like outside air, and freely moves inside and outside. Once the windows, doors and a ventilation system are installed, the building is placed “under pressure.” If more force is directing air into the building than out, it has positive pressure. The opposite is also true. If more air is directed out than in, the building has negative pressure. When that happens, negative pressure makes up the difference by forcing air (and pests) in from every window (drive-thrus especially), door and gap.

When a commercial/industrial facility is built, air pressure needs are assessed, and a HVAC system is designed to introduce enough “treated” fresh air to keep air pressure as close to neutral as possible without becoming negative. This treated, or filtered, air is called make-up air. Considerations for needed make-up air include estimating how much ventilation the facility will need and how much air will be exhausted from equipment. For instance, if a piece of food-processing equipment will be exhausting through a roof vent, the facility needs to make up the difference to keep air pressure in check.

You may notice NP issues arise when a facility adds equipment or ventilation. During the excitement of growth, the process of quickly installing new equipment and budgetary pressures may mean not conducting a formal building pressure diagnosis, and make-up air might be neglected. Though it seems like a harmless oversight, the extra exhausted air creates pressure without notice (as in my previous example) and the pressure void demands NP. Immediately, nearby gnats, who are enjoying their brief life outside, are vacuumed into the harsh interior of your facility.

TURN A NEGATIVE INTO A POSITIVE. You can help your client navigate the challenges of NP by following these three steps:

  1. Identify the presence of NP by performing the tissue test during production. Be certain that the facility is in full operation during the test (all exhausting and ventilating equipment is functioning) or else results will not be accurate.
  2. Educate your client on the facts of negative air pressure:
    • Teach them what NP is, how it becomes a problem and its evidence in their facility.
    • Explain small arthropod susceptibility to NP and help your client connect NP to the presence of arthropods in the facility.
  3. Recommend hiring a HVAC contractor to address the building’s NP.
    • Perform a formal building pressure diagnosis.
    • Install a make-up air system to address NP.

In the previous example, my client installed a temporary make-up air system in a seldom-used receiving dock, since the expense of adding make-up air involved significant capital. After a season with the new system in place, they immediately noticed roughly a 95 percent decline in flying insect activity and gladly paid a contractor to install a permanent make-up air system.

THE GOOD WITH THE BAD. Once you have gone through this process with your client, they are on the road to better pest management. However, I understand that your investigative work and education does not come with the normal sales payoff that other pest management work does. This creates a bittersweet opportunity for you to demonstrate the nobility of what you do by offering integrated pest management (IPM) solutions regardless of your personal gain from them. Additionally, you should be proud of your outside-the-box solution to increase your client’s overall food safety.

So, when those flies are driving you crazy, keep your chin up and keep it positive (air pressure, especially). Positive pressure may be just what you need to keep your facilities and our food safe.

Alex Blahnik is an associate certified entomologist and a technical manager for Wil-Kil Pest Control. Wil-Kil is part of the Copesan network of local service providers.

Copesan is an alliance of pest management companies with locations throughout North America. To learn more, visit