In this four-part series on dust collection for the food industry, we’ll cover everything you need to know about air filtration.

Filtration efficiency is an important element in dust collection system design for the food industry. By selecting the appropriate filters based on the specific needs of the environment, food processes and ingredient handlers can ensure a safer, healthier workplace and avoid cross-contamination concerns while maintaining compliance with air quality regulations. Here are a few things to know.

What Is Filtration Efficiency?

Filtration efficiency refers to how well a filter removes particulate matter from an air or fluid stream. In more technical terms, it is the ratio of the amount of particulate matter retained by the filter to the total amount of particulate matter present in the incoming air or fluid stream, multiplied by 100. For example, if a filter has a filtration efficiency of 90% for particles of 1 micron in size, it means that 90% of the particles that size are captured by the filter, while 10% pass through. Filtration efficiency is often specified for particles of different sizes, as filters may perform differently depending on the particle size. Common particle size categories include:

• Larger particles (e.g., 10 microns and above)
• Medium-sized particles (e.g., 3 to 10 microns)
• Fine particles (e.g., 0.3 to 3 microns)
• Ultra-fine particles (e.g., below 0.3 microns)

Air filters, such as dust collector cartridge or baghouse filters, are commonly rated using the  Minimum Efficiency Reporting Value (MERV) system developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Under the MERV system, which rates filters from 1-16, a higher rating indicates that the filter does a better job at removing smaller particles from the airstream. MERV-rated filter media must be measured using standardized testing methods set by the ASHRAE 52.2 testing standard. [Note: dust collector efficiency ratings fall under the ASHRAE 199 standard, which tests how the filters perform in the dust collection system under real-world conditions.]

Other rating systems for air filters include HEPA (High-Efficiency Particulate Air) and ULPA (Ultra-Low Penetration Air). HEPA filters must capture at least 99.97% of particles as small as 0.3 microns, while ULPA filters must capture at least 99.999% of particles down to 0.12 microns.

MERV Rating Chart

Selecting Filters with the Appropriate Filtration Efficiency

Filtration efficiency is a critical factor in selecting the right filter for a given application, ensuring that the desired level of air purity is achieved. To determine the best filtration efficiency for a specific application, food manufacturers should ask the following questions.

• What is the particle size distribution for the dust being collected? Dust produced in food applications may range from heavy, coarse dust (e.g., dust from bulk grain, seed and nut handling, hulling and mechanical processing) to fine powders (e.g., cocoa powder, powdered sugar, and flour dust). Many processes—including milling, sifting and screening, mixing and blending—produce dust characterized by a wide range of particle sizes. Smaller dust particles require filters with a higher filtration efficiency (i.e., a higher MERV rating) for effective capture.
• What are the application’s cleanliness requirements? In some parts of the food industry, a little dust doesn’t matter much (so long as it does not build up in the air to potentially explosive levels). For applications like bulk ingredient handling, it may not be necessary to have filters capable of capturing all of the smallest particles. A basic MERV 11 cartridge filter may be appropriate for these applications. However, other applications, such as packaging lines, are far more sensitive. Higher filtration efficiency may also be necessary or desirable in environments where cross-contamination is a concern, such as when handling ingredients that are potential allergens. These applications may require higher rated dust collector filters (MERV 15 or 16) or even a HEPA after-filter.
• What are the human health concerns? Fine food dust, such as flour and spices, can cause lung damage and other health issues when inhaled in occupational settings. Food dust can also cause allergic reactions in workers with continual exposure. It is important to consider the air quality requirements necessary for a safe, comfortable and OSHA-compliant workplace. Many food dusts fall under OSHA’s definition of “nuisance dusts,” which have a Permissible Exposure Level (PEL) of 15 mg/m³ for total dust and 5 mg/m³ for respirable dust. Other ingredients—such as sodium metabisulfite, silicon dioxide, and benzoyl peroxide—have lower PELs that must be met. Filters with a higher filtration efficiency rating will help to minimize worker exposure to fine and potentially hazardous airborne food dust.

These questions will help food manufacturers and ingredient handlers determine the efficiency rating needed for their applications. It all comes down to: What is the smallest particle you need to collect? And what percentage of those particles must be collected to meet the desired air quality standard?

Filtration Efficiency and Dust Collection System Design

There are several considerations when choosing filters for a dust collection system.

• Efficiency rating: Dust collector cartridge filters generally come with efficiency ratings between MERV 11 and MERV 16. Some dust collectors can also be fitted with a HEPA after-filter. Keep in mind that for cartridge dust collectors, as the cartridge builds up a dust cake, efficiency for all filters will approach MERV 16. However, when dealing with fine dust and high cleanliness requirements, it is important to select a filter that will provide appropriate filtration across its entire life.
• Pressure drop: While it is important to select a filter that provides the level of filtration you need, it can be counter-productive to choose filters with a higher filtration efficiency than required. That’s because there is a tradeoff between filtration efficiency and energy efficiency in the dust collection system. Filters with higher filtration efficiency become loaded more quickly, resulting in higher pressure drop across the filters. This makes the system work harder and expend more energy. Higher efficiency filters may also need to be changed more often, resulting in higher maintenance costs.
• Odors and gases: If odors and gases are a concern, it may be advisable to have an activated carbon after-filter in addition to dry particulate filters. Activated carbon filters work by adsorption (molecular filtration); they do not collect particulate and do not fall under the MERV efficiency rating scale. However, they can be an important addition to a system where odor control is needed.
• Combustion risk: It is important to remember that almost all food ingredient dusts are combustible under the right circumstances, and this impacts filter selection and system design. Filtration efficiency must be adequate to prevent combustible dust from accumulating to explosive levels in the facility or enclosures. It may also be advisable to select anti-static filters when handling combustible dusts.

If you’re not sure what efficiency rating is needed for your application, a qualified engineering firm can help you evaluate your processes and dust characteristics, determine the hazard level and PEL requirements, and make recommendations for filter media. The right filter will ensure a safe and healthy working environment, contamination-free lines and an efficient dust collection system.  

Learn more about air filtration in the rest of our series:

• Choosing a Dust Collector: Understanding Your Options
• Choosing the Right Filter Media for Your Application
• Care and Maintenance of Cartridge Filters (coming soon) 

For more information, download the Cartridge Filters Buyers’ Guide