Four Keys for Effective Clean/Dirty Lines for On-Farm Biosecurity, By Todd Thurman, SwineTex Consulting Services, LLC


The concept of a clean/dirty line is one of the most basic, fundamental concepts in on-farm biosecurity and perhaps the most important. It’s also one of the most common problems I see when I conduct biosecurity audits. The idea of a clean/dirty line is simple. The clean/dirty line represents the “border” of the farm. When you’re outside the farm, you’re on the “dirty” side because there are a variety of potential pathogens present that we don’t want on the farm. When you’re inside the farm, you’re on the “clean” side. I always tell people that if you get confused as to which is which, always remember that, ironically, the clean side is the one with all the poop.

One of the biggest biosecurity risks, aside from introducing new animals to the farm, is people and things that come onto the farm. People and inanimate objects can serve as vectors for disease transfer by bringing potential pathogens to the farm on their bodies, on their clothing (especially shoes) or on the surfaces of tools, supplies or equipment. With pathogens that don’t travel effectively through the air, such as African Swine Fever, the clean/dirty line is our best defense against the entry of pathogens through people and things.

There may be multiple clean/dirty lines on the farm. Many times there is a clean/dirty line when crossing the exterior perimeter of the farm which may require a change of boots and additional procedures and another clean/dirty line to enter the interior perimeter that may require a complete shower in/shower out process. Clean/Dirty lines also apply to equipment and supplies where hand disinfection, fumigation or UV light are used. The rooms where these activities take place should have a clear distinction between the dirty and clean sides just like rooms where people enter and exit.

Below are four key concepts to consider as you implement or work to improve the implementation of clean/dirty lines on the farm:

· Limiting Entry Points

· Clear, Physical Barrier

· Detailed Instructions

· Consequences for Non-Compliance

Limiting Entry Points:

In order to effectively implement clean/dirty lines, we must first control and limit entry points into the farm. The appropriate number of entry points will be determined in part by farm size and farm design but we want to limit entry points as much as possible so we can focus our efforts on the few remaining entry points. By eliminating multiple entry points, we funnel people and things through more controlled processes that are more easily monitored and audited.

Entry points should be clearly marked with signage indicating that people should enter here. Likewise, any doors that are not entry points should be locked and fitted with signage indicating that this is not an allowable entry point. In some cases, for safety reasons, we may need to leave these doors unlocked so they can serve as emergency exits/entrances. In that case, we must ensure that signage clearly indicates that these doors are only to be used in an emergency and staff must be trained that emergencies involve fire, blood and potential loss of life and limb, not forgotten cell phones or short cuts to checking feed bins. Improper usage of an emergency entry/exit should be punishable with serious consequences.

Clear, Physical Barrier:

One of the most common problems I see with the implementation of clean/dirty lines is the absence of a physical barrier. A line painted on the floor, a threshold or a general area is not a sufficient clean/dirty line. There must be an actual physical barrier that 1) clearly and accurately defines the clean/dirty line and 2) makes it obvious to any reasonable person that something needs to happen before crossing the line. One example of a physical barrier is a bench that goes across the hallway or door. These barriers are designed to be sat on while shoes are removed before swinging your legs over and placing bare or socked feet on the other (clean) side.

An Example of What Not to Do. No clear physical barrier results in shoes sitting ON the line and footprints show that line has been violated.
An Example of What Not to Do. No clear physical barrier results in shoes sitting ON the line and footprints show that line has been violated.

I commonly see situations where people are asked to change boots or put boot covers on when entering a room. This almost completely defeats the purpose of a boot change because people are often stepping on the same ground with their new boots/boot covers that they stepped on before. Essentially, they re-contaminate their new foot coverings with whatever they had on their old foot coverings because there’s no clear difference between the clean side and the dirty side. Another common problem I see is lines spray painted on the floor. The main problem with this method is that people sometimes don’t even realize it’s there or realize it’s there after it’s too late.

A Good Example of a Physical Barrier. Any reasonable person should realize they need to do something before crossing over.
A Good Example of a Physical Barrier. Any reasonable person should realize they need to do something before crossing over.

Detailed Instructions:

So far, we’ve limited the entry points and provided a physical barrier at official entry points that makes it clear to employees and visitors that SOMETHING needs to happen before crossing the barrier. Now, it’s time to tell them exactly WHAT needs to happen. It is critically important that this communication is very clear and explains the necessary procedures in a step-by-step manner. Here’s an example of a procedure for entering the exterior perimeter from one of my clients:

1) Leave all jackets, coats and personal belongings, including anything in your pockets such as keys, phones, bags, notebooks etc, in the provided lockers. The only things allowed through this stage of the entry process is you and your clothing (minus your shoes). The only exception is eyeglasses or hearing aids which must be disinfected with the equipment provided after you wash your hands.

2) Sit down on the bench at the doorway. Remove your shoes and swing your feet over the bench without touching you bare/socked feet to the floor on the “dirty” (non-farm) side.

3) Place your feet in the slippers provided on the “clean” (farm) side.

4) Walk directly to the sink and wash your hands with hot water and soap provided for at least 45 seconds. Ensure you utilize the brush provided to scrub under your fingernails.

5) If necessary, use the disinfectant spray or wipes provided to disinfect eyeglasses or hearing aids.

These instructions should be explained verbally to all employees and visitors and should be posted in a written form at every entry point. Visual diagrams, pictures or illustrations of procedures are also very helpful.

Consequences for Non-Compliance:

It is critical that employees and visitors understand that strict compliance with these procedures is mandatory 100% of the time. A farm manager that I worked with in Russia one time told me that if there was a rabid bear rampaging through the farm, he was sure his workers would shower out before leaving the farm. Every farm’s policies are unique, but it is extremely important that workers understand the importance of compliance with biosecurity procedures. They must also understand that failure to comply with biosecurity policies, including those related to clean/dirty lines, will result in serious consequences based on the farm’s policies. I think it’s important that those consequences include the possibility of termination of employment. In today’s environment, there’s simply too much on the line to have flexibility in enforcement of biosecurity policies and procedures.

The effective implementation of clean/dirty lines is a critical part of any on-farm biosecurity program. These four key concepts, if effectively implemented, will have a dramatic impact on reducing the risk of introducing potentially devastating pathogens into the farm.

About the Author:  

Todd Thurman is the owner of SwineTex Consulting Services, LLC, a US-based provider of consulting and training services for the global swine industry. He can be reached at You can find more information about SwineTex at



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