When the Montreal Protocol and U.S. Clean Air Act declared the fumigant, methyl bromide, an ozone-depleting chemical and phased out its use in 2005, food processing facilities were challenged to develop new solutions for managing insect pests.
Registered for food processing facilities, cylinderized phosphine is an option. However, it tends to corrode metals especially at high humidity levels—and therefore is not commonly used. Sulfuryl fluoride, a non-ozone depleting fumigant, previously used for termite management, quickly became an alternative to fumigate food processing facilities. Sulfuryl fluoride dosages needed are three times that of methyl bromide, and at temperatures below 81 degrees Fahrenheit, it is less effective against the eggs of stored-product insects.
To discover safe, effective alternatives to manage the insect populations, entomologists and practitioners looked to heat. Thermal remediation, often referred to as heat treatment, is a method of heating a mill between 122 and 140 degrees Fahrenheit to strategically eliminate insects.
Insects may try to “hide” within equipment or hidden spaces to escape the heat treatment.
Bhadriraju Subramanyam, PhD, professor at Kansas State University, studies heat treatment and other tactics for managing insect pests in grain, food, and feed manufacturing facilities. His research shows that heating food processing facilities between 122 and 140 degrees Fahrenheit will kill insects at all life stages, without introducing harmful chemicals. The treatment must be maintained over a period of 24 hours so the heat can penetrate cracks, crevices, and equipment, ensuring there is no place for the insects to seek refuge from the heat. In addition, facilities must undergo thorough sanitation prior to heat treatment.
According to Dr. Subramanyam, the optimum temperature for maximum insect survival, development, and reproduction is between 82 and 90 degrees Fahrenheit. Lower and upper temperature limits, in general, for stored-product insect existence are between 55 and 105 degrees Fahrenheit. Temperatures 122 degrees Fahrenheit or above can disrupt the ionic balances across cell membranes, injure cellular DNA, dehydrate insects, destroy protein synthesis machinery, or denature enzymes—all of which can cause insect death. Depending on the insect species and the life stage exposed, death occurs within minutes to hours at these high temperatures.
While high temperatures are an important factor, maintaining the temperature for a sufficient time is also critical because heat needs to encompass all parts of the facility. For example, insects may try to “hide” within equipment or hidden spaces to escape the heat treatment. To eliminate this risk, it is important to thoroughly clean the facility and equipment, and maintain high temperatures (target 135 degree Fahrenheit) for at least 24 hours. According to Dr. Subramanyam’s research, a typical heat treatment from setup to cool down lasts about 30 to 48 hours. Insects may also seek refuge in product spillage. Removing any food products and packaging materials is critical to mitigating this risk.
Risks of Heat Treatment
While heat treatment is an optimal solution for managing pests, it can present risks to the facility if the temperatures are not properly controlled. Excessive, prolonged heat can potentially damage the mechanical structure in facilities, or even its electrical components. Since materials expand and contract at different rates, mechanical components or even the building structure can be compromised if temperature is elevated too quickly. Furthermore, electrical components exposed to excessive heat outside of their recommended operating temperature can fail. The rate of heating should be slow and a temperature of 122 degrees Fahrenheit should be attained in about 10 to 12 hours.
Temperatures should not exceed 140 degrees Fahrenheit.