Unless appropriately leak tested, the operation of the PHEAF device may be a mirage of occupant protection.
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 DEVICE DESIGN AND OPERATION 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.
Using PHEAF Devices during Indoor Renovation and Environmental Remediation
Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers