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Departments - AIB

Answers to Your Toughest QA Questions.

February 8, 2013

Q.  We have some exhaust stacks in our production area above equipment that produce a lot of heat. There are no exhaust fans on the exhaust pipes and the heat just rises up. Is there a standard schedule for cleaning these, or is it just when we think they need it?

A. Great question with many variables. There are questions that would need to be answered to determine the risks from these exhaust systems to the product beneath them. The cleaning frequency would depend on the type of products you make and what is going up into the stacks. Let’s look at a couple common situations.

Oil collection is a probable issue for fry operations. Oil tends to stick to the interior surfaces and, due to cooling temperatures, can build up inside the ducts. At some point, the oil can reach a temperature where it polymerizes, and it may even carbonize like it does on the outside of the fryer. With enough buildup, there is a risk of the material releasing from the sides and falling into the product stream or of excess oil accumulations liquefying and running down the interior of the duct. Besides being a food safety risk, the oil accumulations also present a significant fire risk.

To avoid this, you need to add the ducts to your self-inspection program so they are inspected for buildup that could cause a problem. Based on your inspections, cleaning is then scheduled. In time, you can establish a reasonable schedule to clean the stacks to minimize any issues.

If these exhausts are in a dry processing area where surplus heat from an oven operation is being removed and they are close to an area where dusty products are being used, there is a higher risk of product falling off the duct interior and insect issues developing. Your self-inspection program once again is the primary tool used to monitor the condition of the interior of the duct work and the roof areas around the ducts to determine the frequency of cleaning that is needed.

Facilities often do not have the equipment to do the cleaning as well as it should be done. They often rely on an outside contractor who specializes in cleaning the type of duct work present. Unfortunately, cleaning is put off as long as possible and often done only after an issue with product contamination has occurred because of the costs of these cleaning operations. However, as a rule, the cleaning is less expensive than having product returned by a customer or having it removed from the marketplace.

So, as you are inspecting the interior of the duct systems, look for loose materials that may become dislodged and fall into product runs. Often, particularly with a dry system, circular brushes slightly bigger in diameter than the duct work tethered on a line can be used to keep the interior of the duct work free of loose material and reduce the number of detailed cleanings needed.

These systems can become an important source of product contamination if not properly maintained. You may want to place the inspection of these units on your Master Cleaning Schedule as a reminder to do these inspections and avoid a potentially costly issue.


The author is Head of Food Safety Education, AIB International. Do you have a question for Al St. Cyr? If so, e-mail him at