Disaster losses and the facility restoration process commonly involve the release of a wide array of contaminants into the air including microscopic bio-pollutants, larger, visible particles and unpleasant odors.



Disaster losses and the facility restoration process commonly involve the release of a wide array of contaminants into the air including microscopic bio-pollutants, larger, visible particles and unpleasant odors. Portable HEPA Filtration Devices (HFDs) that can effectively and efficiently capture them can provide one of the most important tools at a remediation contractor’s disposal, with numerous potential benefits, including:
  • Enhanced productivity & work quality
  • Improved work area health and safety
  • Reduced cleanup time
  • Limiting the area of contamination
  • Increased customer satisfaction
  • Faster job clearance & re-occupancy
  • Reduced risk of re-contamination or call-backs


What Is a "True" HEPA Filter?

HEPA (High Efficiency Particulate Air) filters, also known as absolute filters, are much more efficient than other types of filters for removing microscopic particles from the air. By common definition a HEPA filter must provide 99.97% minimum efficiency during use. In other words, no more than three out of 10,000 particles (0.03%) of the 0.3-micron particles pulled in can pass through.

Filters must meet Institute of Environmental Sciences and Technology (IEST) Recommended Practices that cover filter media, filter media testing, filter design, construction and labeling, and completed filter testing.

Are All HFDs Equipped With True HEPA Filters?

HFDs and the filters used in them can apparently fall well short of HEPA performance based on various industry studies and in-field testing. The differences can be much larger than they perhaps seem. Compared to HFDs with true HEPA efficiency, a 99%-efficient HFD will have over 30 times more leakage, a 97%-efficient HFD 100 times more leakage, and a 95%-efficient HFD over 165 times more leakage!

What Causes Less-Than-HEPA HFD Efficiency?

Some of the more common causes of reduced filtration efficiency can include:
  • Each completed filter was not individually efficiency-tested. The use of true HEPA media is no guarantee that the finished filter will be HEPA efficient because a large percentage of completed HEPA filters require repairs to fix problems such as media damage or improper sealing between the media pack and filter frame. Without testing these problems cannot be found and corrected prior to filter shipment and use. In particular, a low percentage of the aftermarket filters in use today are individually tested per IEST requirements.
  • The filter was not tested at the proper airflow. Completed filters tested at airflows far below the rated airflow of the device in which the filter is used may not provide HEPA efficiency in use. The fact that a filter meets HEPA standards when tested at 500cfm or 1,000cfm airflow doesn’t mean it will when operated at 1,500cfm or 2,000cfm.
  • The filter was not made with micro-glass HEPA media. Some HFD “HEPA” filters are built with synthetic media that has an electrostatic charge applied to it to enhance initial efficiency above 99%. In-use efficiency can be reduced substantially as moisture in the air begins to dissipate this charge. This can force users to replace a costly filter after (and possibly during) each job.
  • The filter is HEPA- efficient but the HFD still leaks. Use of a less-than-HEPA efficiency pretty much guarantees that HFD performance will be compromised, but use of a true HEPA does not ensure overall HEPA efficiency. Leakage elsewhere can significantly compromise the overall integrity of the device by allowing unfiltered air to bypass the HEPA filter.


What Do HEPA Filtration Devices Do?

HFDs help control airborne contaminants during every restoration job, and are absolutely essential for water loss jobs, particularly those involving black water or structural mold contamination. Their most critical task is capturing microscopic bacteria and mold spores released into the air during the drying process, but can also capture larger particles like drywall dust stirred up during demolition and construction activities and, when equipped with carbon filters, odors off-gassed from microbes, paints and other chemicals.

Are There Different Types of HFDs?

Yes. HFDs generally fall into one of three design types, all of which can be used to perform the same tasks:
  • ‘Large Box’ Negative Air Machines (NAM) are boxy-shaped units with galvanized steel or rotational molded polymer cabinets mounted on four casters. Designed primarily for use on large asbestos abatement projects, NAM typically provide the most airflow per purchase cost dollar, but are larger, heavier & more cumbersome than other HFD types. They are not well suited for jobs involving movement up or down stairs or in tight spaces.
  • Upright Portable Air Scrubbers are more mobile units with rotational molded polymer or stainless steel cabinets that are moved by tipping them back and rolling them on two large wheels like a hand truck. These devices typically offer more convenience features than NAM but less airflow per initial cost dollar. However, more and more users today find that upright PAS provide the greatest productivity, mobility and ease of use.
  • ‘Small Box’ Portable Air Scrubbers are small, compact devices with rotational molded polymer or stainless steel cabinets and are typically light enough (35 to 45 lbs) to pick up and hand carry. With peak airflow generally in the 400cfm to 600cfm range they are ideal for smaller jobs. However, because multiple units can be used on larger jobs, small box HFDs are also increasingly popular with restoration companies today.


How and When Should HFDs Be Used?

HFDs should be put into operation immediately at the start of the job and operated continuously until, and in many instances after, all work is completed.

The negative pressure containment mode offers the highest level of assurance against contaminants from the affected space escaping into “clean” areas when only a portion of the structure is affected. A physical barrier is erected to seal off the affected area and HFDs are operated continuously within that area to reduce airborne particle counts. Lower (negative) pressure is created within the affected area by ducting air filtered out. This pressure differential helps protect unaffected indoor areas from contamination.

HFDs are often operated in the recirculation mode whenever the entire indoor space is affected. In this mode no pressure differential is created and there is typically no barrier. The HFD simply continuously filters contaminants from the air to reduce airborne particle counts and exhausts cleansed air directly back into the indoor space.

How Much Airflow Do I Need?

A common industry design parameter is four to six clean air changes per hour (ACH) or more. More is better, and it’s prudent to increase the design ACH to build in a margin of safety for airflow losses due to factors such as filter loading or exhaust ducting. If you need 5 ACH for example you might design for 6 ACH. Here’s a fast and easy way to figure out the total cubic feet per minute (cfm) of airflow required:
  1. Calculate the total air volume in cubic feet by multiplying the length times the width times the height, all in feet. If there is a contained work area, use the dimensions within that area. If there’s no physical containment barrier the volume of the total space must be used.
  2. Divide the air volume by 10 for 6 ACH, by 12 for 5 ACH, or by 15 for 4 ACH.
Example: The minimum airflow required to maintain 6 ACH in a 30 ft. x 20 ft. x 10 ft. contained work area would be calculated as follows:
Volume = 60 ft. x 20 ft. x 10 ft. = 12,000 cu. ft.
Airflow Required for 6 ACH = 12,000 / 10 = 1,200cfm

HEPA filtration device can help mitigate a lot of problems. Do your homework, select them carefully, and use them properly and you, insurers and their customers can all benefit.