Designing Your Hygienic Zoning

Features - Facility Management

Process flow is a critical aspect of sanitary design.

February 5, 2019

By Lisa Lupo

Sanitary design is nothing new, but you may be surprised to learn that mention of the term can be found as far back as 1884. An article in American Architect and Architecture magazine cited a paper by Benjamin Ward Richardson M.D. stating that absolute cleanliness “is the beginning and the end of the sanitary design, and that such perfect cleanliness would wipe off all the diseases which cause at this time the leading mortalities.” While Richardson was focusing on the public sewer and drainage systems, a 2010 article in Concrete magazine discusses how use of concrete floors and smooth plastered walls can make a dairy easy to clean “but offers no particular requirements in the way of sanitary design”; ads in at least two 1912 magazines tout the “sanitary design” benefits of their dairy equipment; and a 1916 article discusses Columbia University classes in sanitary design.

With such history, of which these examples are just a snippet, it’d be natural to think that sanitary design would be a fundamental aspect of every food processing facility. But while many facilities do focus on at least some aspects of sanitary design, just as many others are unsure of what, exactly, sanitary design is and how to apply it in an existing plant.

DEFINING SANITARY DESIGN. In essence, sanitary design is just what Richardson purported in 1884: the design of a facility and its processes that would be a significant step to “wipe off all the diseases which cause at this time the leading mortalities” (or in our case, the foodborne disease illnesses and mortality). Today’s definition, as stated by the North American Meat Institute is “the application of design techniques which allow the timely and effective cleaning of the entire manufacturing asset.” Its purpose is to “prevent the establishment of soils in a niche (bacteria biofilms, allergenic proteins) or other sites that can lead to contamination of products that will impact product quality and safety.”

The goal of sanitary design is to assist manufacturing and storage facilities in the design, installation, and maintenance of buildings and equipment to prevent the inclusion or introduction of physical, chemical, or microbiological contaminants. Many sectors of the food industry have specific sanitary design standards that are outlined in regulations, including: dairy, meat, produce, and milled or grain-based materials.

While each sector has unique challenges and requires specific design requirements to address specific issues, sanitary design has four general areas of focus:

  1. Premises, surroundings, and building site.
  2. Exterior building design and construction features.
  3. Interior building design and construction features.
  4. Operational flow and facility layout.

Because covering all aspects of sanitary design would make up an entire book (and has done so), the purpose of this article is to provide a general overview, then focus in on sanitary design principles that can be applied to the processes and flow of food production — no matter how old, new, large or small the facility may be. Thus, our primary area of focus is #4: Operational flow and facility layout. To that end, the following compiles information and recommendations from Ron Schmidt and Daniel Erickson, University of Florida/IFAS Extension Sanitary Design and Construction of Food Processing and Handling Facilities; Tim Freier, Mérieux NutriSciences 3 Considerations for Your Hygienic Zoning Practices; and AIB Food Safety and Sanitation Distance Learning Course.

HYGIENIC ZONING. Ideally, a facility should be designed to provide a flow pattern for food products, personnel, and equipment to prevent contact of the finished product with raw materials. Flow should be in one direction and follow a logical sequence from raw material handling to finished product storage. Within this flow should be the concept of hygienic zoning. That is, dividing the facility into defined areas based on food safety risks. This is commonly used to control microbiological risks but also is applicable for other segregation needs, such as allergen control, physical hazards, or GMO versus non-GMO. With the too-common incidence of Listeria-contamination food recalls today, zoning has become very important, and hygienic zoning continues to be a hot topic, with better zoning and better sanitary design of equipment often going hand-in-hand with development or improvements of environmental monitoring programs.

Often, however, there is confusion between hygienic zones and environmental monitoring zones. Although the two are related, they are separate concepts:

  • Hygienic zones are created within the facility based on the risk of cross-contamination to the product.
  • Environmental monitoring zones are commonly divided into zones 1 to 4 for the purpose of targeting environmental sampling for pathogens such as Listeria or Salmonella.

Thus, three key aspects of hygienic zoning are physical separation, process flow, and employee practices and training.


1. Physical separation.
As much as is practicable, there should be a physical separation between raw and finished products and minimal entry into critical areas. Such physical separation should be accomplished by installation of walls and doorways with anti-backtracking features, and by adjusting air handling systems to provide positive pressure in finished product rooms. As the best physical separation can be undermined by human error or improper personnel flow, there should be an operational and philosophic separation between raw and finished product. It is recommended that standard operating procedures be developed and implemented regarding product flow.


Thus, the hygienic zones within your facility can be divided physically or through the use of special practices, such as a requirement for employees to wash their hands or wear special shoes or clothing. Commonly, manufacturers would prevent microbial cross-contamination by dividing the raw side of their facility from the cooked side. Divisions could also be made between dry and wet areas, treated versus untreated areas, or allergen-containing versus non-allergen areas. Most facilities also have non-manufacturing areas, such as offices, locker rooms and cafeterias, which would be a third defined hygienic zone.

The degree of hygienic control in each zone is based on the risk of product cross-contamination. For example, a plant could have a fourth zone if it is producing a high-care product, such as ready-to-eat (RTE) foods designated for consumption by infants or other higher-risk groups.

Ideally, raw, potentially contaminated ingredients would enter one end of the facility, with product undergoing a kill step as it is piped or conveyed through a wall.

Another term often used in connection with hygienic zoning is the Primary Pathogen Control Area (PPCA). The product passes through this area after the pathogen kill step and is exposed to the environment here before being sealed in the final package. The stringency of controls in the PPCA depends on the intrinsic characteristics of the product, the degree of exposure of the product to the environment and the degree of handling or processing of the product.

Separation can also be accomplished by the installation of sanitizer systems (e.g., foot baths, spray systems) inside entrance doors to critical areas. It is imperative that these systems be maintained in good repair and that they be used. Visitors, suppliers, laboratory personnel, inspectors, management, and all other individuals should be made aware of operating procedures with regard to separation between raw and finished products.

2. Process flow.

Properly designed traffic patterns will create a more economic operation, reduce possible safety concerns or accidents, and minimize cross contamination or food safety concerns. The ideal plant layout would have raw, potentially contaminated ingredients entering one end of the facility, a place for processing in the raw area, and then product undergoing a scientifically validated kill step as it is piped or conveyed through a wall into the PPCA. After packaging, the product would be conveyed through another wall into the storage area.

Obviously, you cannot design a manufacturing facility as a series of sealed boxes; people and items need to be able to move between the zones. Thus, manufacturers can establish a buffer/transition area between hygienic zones to reduce the risk of contaminants moving from a dirtier or lower risk zone to a cleaner or higher risk zone.

When conducting self-inspections by quality assurance personnel, regulatory inspections, or tours, a counter product-flow direction should be taken, starting with finished product and ending in raw material handling areas.

In addition to providing procedures for personnel and equipment within the facility, the movement of equipment in and out of the facility by maintenance crews should be considered. Color-coding is often used with different colors identifying different areas of the facility. This can be applied to cleaning supplies (e.g., brushes, brooms, pails); containers (e.g., pails, lugs); gaskets, forklifts, and other equipment; and worker uniforms.

Because manufacturing environments can change even within the same building, this can create food safety and product integrity challenges. Product flow sheets are useful in helping to identify potential problems in the design or redesign of a system or process. Consideration should be made to:

  • Identify wet and dry manufacturing areas so that walls and barriers can be established to prevent moisture and dust from traveling between areas.
  • Establish air-handling systems, ventilation, filtration, and air exchange to prevent mold and condensation problems.
  • Install central vacuum systems and dust control methods to maintain a clean work environment which also will improve employee work areas.
  • Identify the locations of initial raw material (e.g., grain commodities) cleaning so that insects and other foreign material can be removed; and provide adequate space for cleaning activities.
  • Provide adequate lighting in all areas of the facility.
3. Employee practices and training.

There will be situations and areas where neither a physical barrier nor the ideal traffic flow makes sense, so employee practices and training will be essential. When zone segregation depends on employee practices, the challenge will be ensuring that these are followed diligently, with success often directly related to the food safety culture within the facility.

Barring employees in raw materials from entering finished product rooms can significantly reduce the opportunity for cross contamination. Ideally, employees designated to work in the PPCA would have their own locker room, cafeteria and maintenance area with PPCA-designated tools and equipment, and raw side employees never seeing or coming into contact with PPCA employees during work hours. Clean, filtered air would flow from the PPCA to the other zones, and wastewater lines would run from the PPCA to the other zones.

Science-based risk assessments can help determine the most impactful separation techniques, process flow, and employee practices and training. The overall intent of sanitary design hygienic zoning is to keep finished products that are susceptible to microbiological or allergen issues isolated so they are not contaminated by raw and untreated materials or allergenic ingredients.

The author is Editor of QA magazine. She can be reached at