Mold Air Filtration

Why Restoration Contractors Use AFDs On Mold Damage Projects

• Employee Health and Safety:

  • Mold remediation projects often disturb settled dust and debris, creating airborne particulates that can pose significant health risks to employees, even wearing respiratory protection.

• Dust and Debris Control:

  • Restoration activities, such as demolition, material removal, and cleaning, generate substantial amounts of dust and debris.

  • AFDs effectively reduce the #s of these particulates, preventing them from spreading throughout the structure and becoming breathable.

  • This is especially important when dealing with materials that may contain irritants or allergens.

• Contaminant Removal:

  • Mold remediation can introduce various contaminants into the air, including:

    • Fine particles from demoed building materials.

    • Microbial fragments associated with mold & bacteria.

  • HEPA filters are designed to capture particles at 0.3 microns with a high efficiency rate, effectively removing these contaminants from the air with 99.97% efficiency at this particle size.

How AFDs Work:

• HEPA Filtration:

  • HEPA filters are composed of a dense network of fibers that trap airborne particles.

  • They achieve their high efficiency through a combination of interception, impaction, and diffusion as a means of trapping particulate.

  • They're tested against particle sizes of .3 microns. This particle size was selected by the CDC (Centers for Disease Control) & the AMA (American Medical Association) as being the deepest penetrating breathable particle type. 

• Airflow Management:

  • AFDs draw air through the HEPA filter, removing particulates before discharging clean air back into the environment.

  • Proper placement of AFDs is essential to maximize their effectiveness.

  • Creating negative air pressure by exhausting the filtered air outside of the structure, is often the best method.

Practical Considerations:

• Filter Maintenance:

  • Regularly inspect and replace HEPA filters as the are either contaminated, or become loaded with particulate to ensure their optimal performance.

  • Clogged filters reduce airflow through the AFD.

    • HEPA filters must never be removed & replaced while in service on a project. In the event that it's required to replace the filter in the field, seal the unit up, take the unit outside, away from the project & perform the swap.

• Unit Placement:

  • Position AFD intakes as close to where contaminants are, or where work is to be performed to capture airborne particulates at their source.

  • Consider using multiple AFDs in larger or heavily contaminated areas.

  • Determine the amount of air filtration required in CFM.

1. Determine the Volume of the Space:

• Measure the Dimensions: Measure the length, width, and height of the room or area in feet.  

• Calculate the Volume: Multiply the length, width, and height to find the volume in cubic feet (ft³).

  • Example: An area that is 45 feet long, 36 feet wide, and 8 feet high has a volume of 45 ft x 36 ft x 8 ft = 12,960 ft³.

2. Calculate the Total Air Volume to be Changed:

• Since we want 4 air changes per hour, we need to divide the volume of the room by 15 (or 1 air change every 15 minutes).

  • Example: 12,960 ft³ / 15= 864. This means we need 864 cubic feet per minute to achieve 4 air changes per hour.

3. Calculate the Required Number of AFD Units:

• Using the CFM rating of the AFD, we must divide the CFM required & divide it by the AFDs rating.

  • Example: You have available 500 CFM units. 864 / 500. This gives a value of 1.72. 

  • Since this isn't a whole number we must round the unit up to 2.

  • Technicians would setup two 500 CFM AFDs in the property.

• Practical Considerations:

• Air Filtration Devices (AFDs): When using AFDs, their CFM rating indicates how much air they can move. Choose an AFD with a CFM rating that meets or exceeds the calculated requirement.

  1. • Be mindful that the CFM of the AFDs may be misadvertised by the manufacturer.

     • Some manufacturers will use a CFM rating without the HEPA filter in place. The amount of resistance to flow the HEPA filter creates can greatly minimize the actual CFM of the AFD.

       • This seems to be more prone to the larger AFD's vs the smaller 500 CFM units. For example a unit that is rated at 2000 CFM may be lucky to see 1600 CFM with the HEPA filter installed.

     • Attachment of ducting to the units can create a restriction that reduces overall airflow through the AFD. 

Filter Changes: 

The filters in AFDs should be swapped frequently to keep the airflow through the unit as high as possible. Loaded filters slow air down & can cause issues with the air changes per hour originally factored.

• Prefilters: 

  • Spun poly filter: should be swapped at the end of the day minimum.

    • This filter may require replacement during heavy dust generating activities such as using saws & sanders.

  • Pleated filters: should be swapped at the end of each day.

  • Primary/HEPA filter: This is generally replaced after 20-30 days of use, or after it's used on a project such as fire & smoke, or a sewage or trauma project where odors have permeated the primary filter. 

    • There is unfortunately no decontaminating these filters. Ozone & hydroxyl will damage the adhesives that hold the fabric to the housing.

Additional Terminology:

• Air Scrubber: this refers to an AFD that is set to neutral pressure.

• Negative Air Machine: This refers to an AFD that's connected to the exterior of the building by ducting to draw the work area under negative pressure.

Module: Air Filtration Device (AFD) and Filter Training

I. Primary Filter (HEPA)

• Function:

  • High Efficiency Particulate Air (HEPA) filters are 99.97% effective at arresting particles at 0.3 micron.

  • They trap ultra fine particulate in it's paper element.

  •  The final filter in a filtration system.

• Operational Requirements:

  • Quality HEPA's must not allow air to bypass when as it becomes loaded with particulate.

  • HEPA's should ALWAYS be used when using an AFD, even when exhausting to areas where exposure is unlikely.

• Alternative Operation:

  • If contractors decide to use an AFD without a primary filter, the unit should be dedicated to this purpose and be clearly marked as such.

  • Prefilters MUST always be used.

  • An AFD without a HEPA should NEVER be used in situations where the exhaust airflow could inadvertently affect any other structures or interact with humans.

  • Perhaps use a damaged AFD that fails a particle counter test for this application.

II. Validation of AFD and HEPA Filter Performance

• Method:

  • Use a laser particle counter to compare air entering and exiting the AFD.

• Example 1 (Acceptable): 

  • Air entering AFD: 58,394 particles at 0.3 micron.

  • Air exiting AFD: 1,699 particles.

  • Calculation: 58,394 * 0.03 = 1750.47.

  • Conclusion: Filter operates at or above 99.97% efficiency.

• Example 2 (Bypass): 

  • Air entering AFD: 99,841 particles at 0.3 micron.

  • Air exiting AFD: 5,822 particles.

  • Calculation: 99,841 * 0.03 = 2995.23.

  • Conclusion: Filter is bypassing particulate.

• Investigation of Bypassing Units:

  • Do not disassemble for the purpose of testing while inside an active project.

    • Remove the unit carefully and replace it with a verified functional unit.

  • Potential issues causing bypassing air:

    • A compromised seal between the filter cartridge and the AFD case.

    • A damaged case due to misuse or abuse.

    • Physical damage to the filter.

• Used HEPA Filter Performance:

  • Undamaged, but used HEPA filters may show lower particle counts in the form of higher arrestance percentage than new filters.

  • By catching more & more particulate, the HEPA module will entrap more material.

  • Efficiency may surpass 99.97%, but CFM throughput is reduced as a consequence.

• Low-Quality AFDs:

  • Cheaper AFDs may not provide an adequate seal between the HEPA filter and the AFD case.

  • Some units have little to no gasket material, resulting in bypassing contaminated air.

III. Particle Size and Filtration

• .3 Micron Significance:

  • The healthcare industry identified particles at 0.3 micron as the MPPS (most penetrating particle size) for human inhalation.

  • Mold tends to be particles 10-15x larger than the test criteria.

IV. HEPA Filter Service Life

• Filter Life Span:

  • It really depends on the particulate material being arrested, the particle counts, and the run time.

• Specific Applications:

  • Smoke, fire, body decomposition, or sewage/bacteria: necessitate replacement upon project completion due to odor permeation and cross contamination risk.

  • Life on normal mold or water losses: Approximately 20 days of run time.

• Airflow Reduction:

  • Operators will see a diminished airflow per day of operation.

  • After 20 days the airflow may be insufficient for the required Air Changes per Hour.

V. Pre-Filters

• Function:

  • Protect and extend the life of the HEPA filter.

  • Trap particles at < 95% efficiency.

  • Must always be used with an AFD.

  • These filters should be swapped daily at the end of the workday after dust generating activities have ceased for the day.

  • Purpose: Knock down airborne particulate after demolition/dust generating activities.

• Types:

  • Spun Poly filter: First filter, typically non-directional. Replaced at least once per day.

  • Pleated filter: Second filter, directional. Replaced once per day, potentially twice during high dust generation.

  • Ring Panel Filter: An optional filter that uses a metal ring around the perimeter to hold the filter in place without collapsing against airflow. This filter protects the HEPA from air bypassing clogged pre-filters. Generally replaced upon the projects completion.

  • Activated charcoal filter: Similar to a pleated air filter, but with odor absorption.

VI. Particle Trapping Mechanisms

• Straining:

  • Particles larger than fiber openings are trapped.

• Impaction:

  • Particles directly impact the filter medium.

  • Affects particles over 1 micron.

• Interception:

  • Particles bump into the side of the filter medium.

  • Affects particles between 0.1 and 1 micron.

• Diffusion:

  • Brownian motion causes very small particles to create a wavy pattern.

  • Affects particles smaller than 0.1 micron.

• Electrostatic:

  • Negatively charged particles are attracted to positively charged fibers.

VII. MERV Rating

• Definition:

  • Minimum Efficiency Reporting Value, established by ASHRAE.

  • Represents the lowest possible performance.

  • Indicates how many particles the filter will trap.

  • Higher the number, the more particles trapped.

  • HEPA has an equivalent MERV rating of 17 or higher.

VIII. Filter Thickness

• Effect:

  • Filters with the same MERV rating trap similar amounts of particulate.

  • Thicker filters (e.g., 2") allow less pressure drop through the filter, resulting in more airflow.

  • Thicker filters contain more filter material surface area compared to the thinner filters of the same other dimensions.

  • Thicker filters also can often go longer between filter changes, relative to a thinner filter of the same MERV rating.

IX. Particle Arrestance

• Misconception:

  • Particles larger than 0.3 micron are not necessarily 100% arrested.

  • Particles smaller than 0.3 micron do not necessarily pass through unobstructed.

    • Particles smaller than .3 micron typically have a higher arrestance rate relative to .3 micron particles. 

• Filter Material Structure:

  • The filter material is not a screen with evenly spaced holes.

  • It consists of random overlapping monofilament strings.

  • Material is composed of hundreds or thousands of layers.