Unless appropriately leak tested, the operation of the PHEAF device may be a mirage of occupant protection.
Considering the short-term nature of environmental remediation and indoor renovation projects, the PHEAF device is designed to be more easily transported than a BSC. Incidentally, these portable units are frequently mishandled and subject to dropping, which could damage the HEPA filter or device cabinet. Sometimes the damage may not be visibly evident to the user, such as a HEPA filter dislodged from its filter mount. An Internet search for images of asbestos abatement projects will illustrate the conditions of PHEAF devices used in the field environment.
The HEPA filter’s efficacy is sensitive to handling and use. To meet expected performance standards, manufacturers mandate careful handling of the filter and proper installation by trained technicians. Testing of HEPA filters at the time of manufacture establishes the quality of particle capture and airflow parameters; however, unless the filter is labeled as such, an industrial hygienist shouldn’t assume that the individual filter was tested when manufactured.
HEPA filters used in BSCs undergo standardized leak testing to verify the efficiency of the filtration device during operation. Several industries have mandated leak testing of HEPA filtration devices. The Department of Energy recommends in-place leak testing of portable HEPA vacuums upon initial use and each time the device is transported to another worksite. The Institute of Environmental Sciences and Technology provides procedural standards for leak testing HEPA filters in cleanrooms. A Canadian organization (Environmental Abatement Council of Ontario) drafted guidelines for HEPA-filtered equipment used on abatement and remediation projects. These test requirements were authored for good reason. Published research has reported that new HEPA filters are not infallible. While most HEPA filters perform as expected, studies have reported failures when tested upon delivery. HEPA filters have also been documented to underperform in the filtration device. Despite evidence indicating that units can be mishandled, national standards requiring performance testing of the PHEAF device are lacking. Unless appropriately leak tested, the operation of the PHEAF device may be a mirage of occupant protection—meaning the absence of visible PM is not an indicator of the filter’s efficiency. Indeed, respirable PM is often invisible to the naked eye.
The case for leak testing the PHEAF device is conceivable; however, one argument against it is that the test equipment is cumbersome and not ideal for use in a field environment. Another drawback is that the test equipment may be expensive to purchase. Fortunately, advances in technology now afford suitable options to the traditional photometer for leak testing PHEAF devices. One deciding factor for selecting the right measurement instrument is a validated protocol for conducting the leak test in a field environment.
In the absence of leak testing the PHEAF device, the industrial hygienist can take other precautions to address obvious concerns:
  • Replace HEPA filters according to the device manufacturer’s recommended practice. A trained technician should be responsible for filter replacement. When the HEPA filter is brought to the project site, verify the change date. The owner or operator of the PHEAF device should know when the filter was last replaced and might describe criteria for determining when the filter should next be replaced.
  • Repair all damaged devices before they are deployed for use. Dents and other damage to the cabinet can cause the HEPA filter to become misaligned in the filter mount frame. Also, inspect and verify that the HEPA media and corrugated separators are not damaged.
  • Exhaust the PHEAF device outside of the building. Exceptions to this rule should be considered only when the industrial hygienist’s professional judgement indicates a low risk of exposure to occupants.
  • Verify that the owner or operator conducts routine inspections of the PHEAF device while it is in service. The inspections should include replacement of the pre-filter and ring filter.
  • Tighten the HEPA filter’s retaining brackets. Loose brackets can allow a gap between the filter gasket and mounting frame.
PHEAF devices provide temporary pollution control during short-term projects, such as building renovation and remediation of hazardous materials. Despite use of these devices in hazardous environments, no U.S. standards have been published for field testing them. The failure of the HEPA filter to perform as intended can result in unintended risk to the building occupants. Science has demonstrated that filtration is a reliable technology for managing dust, but its performance on the job site should not be taken for granted.
Like the stationary HEPA system, the PHEAF device is used as a control for occupant exposure to PM. Both types of devices use filter technology that is subject to failure, but the practice of performance testing is limited to the stationary type. Filter leak testing may be unnecessary if the user has no level of expected protection from use of the PHEAF device. The actual level of filtration—whether it’s 10 percent or 90 percent—may be irrelevant, as any PM reduction is better than none; however, ducting the exhaust air of an ill-performing PHEAF device to building areas otherwise unaffected by the construction activity may cause more harm than good. In other words, the building area would become contaminated from the work activity only because the exhaust air of the poorly performing PHEAF device is exhausted into it.
The performance of the device is of greater concern for occupant safety when exhausted indoors. For example, an airborne asbestos concentration of 0.07 f/cc passing through a PHEAF device with 90 percent capture efficiency translates to an exhaust concentration of approximately 198 f/ft3 compared with 0.6 f/ft3 for a PHEAF device operating with 99.97 percent capture efficiency. When seeking to control PM during more hazardous operations, users should consider other options before ducting the exhaust within the building.
is a commissioned officer in the U.S. Public Health Service and is the acting deputy director, Division of Occupational Health and Safety, National Institutes of Health.
is an associate professor in the Environmental and Occupational Health Department at the Milken Institute of Public Health, George Washington University.
Acknowledgments: Amanda Northcross, PhD, assistant professor in the Department of Environmental and Occupational Health and the Department of Global Health at George Washing­ton University; and Bob Brandys, PhD, CIH, CSP, PE, consultant with OEHCS, Inc. in Las Vegas, Nev.
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Known originally for their use in nuclear air cleaning systems, high efficiency particulate air (HEPA) filters containing specialized media are now commonplace in the biomedical, aerospace, pharmaceutical, and clinical care settings. As an engineering control, HEPA filters are the crux of the biological safety cabinet’s (BSC) performance and are essential for achieving filtration standards in clean rooms. Although HEPA filters were initially promoted for use in stationary filtration systems, they have since become a tool of the trade for the asbestos abatement and mold remediation industries, which necessitate mobile engineering controls. These controls, known as negative air machines, air scrubbers, or portable high-efficiency air filtration (PHEAF) devices, are now a trademark of the environmental remediation industry.
PHEAF devices have also been adopted as a dust control strategy for renovation activities within occupied buildings. Building renovation includes tear-out, interior gutting, and removal of structural components. Techniques that grind, cut, crush, pulverize, and otherwise abrade the building elements introduce dust, fibers, and bioaerosols into the workspace, potentially exposing workers and building occupants alike to particulate matter (PM) if appropriate dust interventions are not in place. Controlling dust to and within the project area can be tricky, and this challenge falls to the industrial hygienist, who must assess and strategize ways to minimize occupant exposure to the unwanted dust.
PHEAF devices come in a variety of shapes and sizes. The traditional boxy cabinet design is fabricated of metal whereas more recent versions have a cabinet molded from polyethylene. Most design types include caster wheels attached to the cabinet’s bottom to ease movement through the building to the project location.
Typically, a centrifugal blower is used to pull contaminated air into the PHEAF device and through the HEPA filter. To accommodate project needs, the PHEAF device usually has a variable air flow rate ranging between 500 cfm and 2,000 cfm. To trap larger particles from contaminating the HEPA filter, a pre-filter and second-stage ring panel filter are usually placed ahead of the HEPA filter.
As an engineering control, PHEAF devices are used in various configurations, depending on the project’s complexity and building dynamics. One application is to use a flexible polyester duct to discharge the device’s exhaust air outside of the containment zone, thereby creating a pressure gradient. Maintaining negative pressure differential between the work zone and adjacent spaces limits PM from infiltrating clean areas. Preferably, the PHEAF device is exhausted outside of the building; however, the absence of window or door openings, or the distance from the building openings to the containment zone, can prevent such an arrangement. In these circumstances, the filtered air is ducted outside of the containment zone and recycled into the building envelope. Other contaminant control strategies include using the PHEAF device as a scrubber to filter and exhaust air within the work zone—essentially recirculating the ambient air.
Table 1. Examples of Reference Documents Citing Portable High-Efficiency Air Filtration (PHEAF) Devices
Tap on the table to open a larger version in your browser.
Over the past several decades, industrial hygienists have witnessed heightened concerns about indoor air quality and health. Adverse health effects associated with legacy toxins such as asbestos and lead-based paint are well understood. But what about particulates often classified as merely nuisance, or, as termed by OSHA, Particulates Not Otherwise Regulated? Nuisance dusts should also be considered for their hazardous properties. Although abatement of asbestos and lead-based paint eliminates a health risk, replacement materials synthesized with complex chemicals may also be hazardous to a building’s occupants, particularly if a toxic material is degraded to a respirable size and becomes airborne. For example, abrading, scratching, and sanding are activities that could degrade building materials sufficiently to release particles into the ambient air.
Building-related illnesses can be difficult to attribute to a specific stressor, but PM is a known adverse health determinant. Those with pre-existing conditions, such as hospital-acquired infections, may be more vulnerable to bioaerosols. For this reason PHEAF devices are considered a complement to infection control procedures during construction-related activities inside hospitals; however, otherwise healthy individuals also can experience health complications due to a building’s air quality. For example, mold contamination on building materials can be aerosolized during office renovation activities, presenting an inhalation hazard to individuals sensitive to biologic agents.
The relationship between ambient PM and adverse health effects has been established, but further studies are needed to determine this relationship within the indoor environment. While science further researches mechanisms of injury, EPA has ranked poor IAQ as a top-5 environmental risk to public health. Excessive PM can degrade IAQ. Uncertain of the exposure-response relationship between indoor PM and adverse health outcomes, prudent practice is to limit exposure to the lowest achievable concentration. Yes, housekeeping is a practical method toward this objective; however, since the early days of OSHA’s asbestos regulation, ventilation has been considered the acceptable means for controlling airborne PM. For this reason, PHEAF devices have become the go-to solution for both environmental remediation and renovation projects that occur indoors.
Over recent decades, a paradigm for minimizing source contamination during interior building renovation has evolved. For some projects, PHEAF devices are elected by the building owner or contractor as a best management practice; other projects require their use through contractual clauses referencing a guidance document or consensus standard. A list of guidance documents and consensus standards is provided in Table 1.
RESOURCES Abatement Technologies: “Important Facts about Anthrax and HEPA Filtration.”
Abatement Technologies: “What to Consider When Evaluating Portable Air Scrubbers.”
ATI Test Laboratory: “Filter Test Facility Report on the Testing of HEPA Filters for the DOE, FY 2010–FY 2nd Quarter 2012” (
, June 2012).
Brookhaven National Laboratory: “HEPA Filter Vacuum Cleaner Testing” (
, March 2001).
Defense Nuclear Facilities Safety Board: Letter on procurement and field testing of HEPA filters, Hanford site (
, July 2000).
Department of Energy: Letter on increased HEPA filter rejection rates (
, June 2010).
Environmental Abatement Council of Ontario: “EACO DOP / PAO Testing Guideline 2013” (
, 2013).
EPA: “
Why Indoor Air Quality Is Important to Schools
Michigan Department of Licensing and Regulatory Affairs: “Guidelines for Use of Portable Air Filtration Systems in Health Care Facilities” (
Mintie Technologies: “HEPA-filtered Negative Air Machines and their Role in Creating Airborne Infection Isolation Rooms with the ECU AnteRoom” (
Nuclear Regulatory Commission: Letter on HEPA filters used in DOE hazardous facilities (
, May 1999).
Using PHEAF Devices during Indoor Renovation and Environmental Remediation