Air Purifiers

What is a portable air purifier?

A portable air purifier (sometimes called an air scrubber) is a self-contained unit which pulls air in from a localized area, passes that air through a filtration and/or purification system and releases the clean (i.e. “scrubbed”) air to a designated location. The clean air can be released into the same area where the portable unit is located, or it may be exhausted via a portable duct to a different nearby location or outside.

These devices are typically used in the construction industry to control dust particles created during renovations, however they can be utilized in any local environment where air quality presents a concern.

Classes

There are no “classes” of air purifiers, but there are many different models available. The two general concepts involved would relate to: a) capacity of unit; and b) type of filtration.

Capacity: different fan sizes and speeds allow for variation in the speed and volume of air which passes through the unit. This capacity is usually measured in a clean air delivery rate (CADR) which reflects the cubic feet per minute (CFM) that passes through a unit. This directly affects the size of an area which can be serviced by a single unit.

Filtration: different models may utilize different types or combinations of filtration. Typical types include:

  • Mechanical Filtration - These are physical filters where the air passes through a dense web of fibers which trap particles. Filters are typically measured utilizing a MERV rating to assess the efficacy of their filtration. The highest filters are HEPA filters, which collect 99.97% of particles up to 0.3 micrometers in diameter. These filters do no remove odors or gases;
  • Activated Carbon Filters - These sorbent filters use activated carbon to absorb some odor-causing molecules from the air, along with some types of gases. These filters do not remove particles;
  • Ozone Generators - These units produce ozone, a molecule which reacts with other pollutants to change their composition. These devices are not recommended for medical environments;
  • Electronic Air Purifiers - Electrostatic precipitators and ionizers charge particles in the air so they stick to plates in the machine in a magnet-like fashion. These devices can also produce ozone and are not recommended for medical environments; and
  • Ultraviolet Germicidal Irradiation - UV lamps have the potential of killing some airborne viruses, bacteria and fungal spores provided the light is powerful enough and the exposures time is long enough.

General Considerations

Before utilizing a portable air purifier, consideration should be given to the size of space requiring filtration. Multiple units may be required to be effective, but the units should be spaced apart sufficiently to allow them to work efficiently.

Portable air purifiers work best in enclosed spaces; plastic vapour barriers are sometimes utilized to ensure that contaminants remain in an isolated area. However, care must be taken to ensure adequate air flow around the unit itself. Portable air purifiers can generate significant fan noise while operating.

Air purifiers require regular maintenance to ensure they are operating correctly. Filters need to be changed at intervals specified by the manufacturer, which represents a significant operating cost. Safe and correct disposal of dirty filters is essential to avoid potentially re-contaminating any area.

Limitations

Air purifiers are effective only in small areas, portable air purifiers cannot replace an overall ventilation system.

Air purifiers can only remove contaminants and allergens which are floating in the air. Larger and heavier particles such as mites, mold and pollen settle to the ground quickly, so air purifiers have only partial success in capturing such particles before they settle. The ability of air purifiers to combat radon contamination is not conclusively known. Depending on how and where the units exhaust their air, the purifier has the potential of increasing air currents in a room.

High humidity or wet environments can cause moisture to accumulate in the filters, severely reducing their effectiveness, potentially causing filter damage or damage to the unit itself. The devices should not be used to “dry out” an area.

Recommended portable air purifier specifications

For a health care environment, multi-stage mechanical filtration is required. The MERV filtration levels required by CSA standards differ from room to room depending on the activity taking place in the room. Typically, having multi-stage filters where the last stage is a HEPA-grade filter is sufficient for health facilities.

How do you know if a portable air purifier is working as designed?

Air purifier performance should be evaluated using a recognized method by a qualified person.

When selecting an air purifier, choose a make and model which provides internal monitoring as to when the purifier is not working correctly or the filters required replacement.

Air purifiers should be inspected, maintained and cleaned at a frequency that is sufficient to protect the health and safety of workers. Records should be kept of all inspections, maintenance and cleaning, including the team member who performed the duties. Records should be readily available to Occupational Health Committees.

References

  • CSA Z317.2-10 Special requirements for heating, ventilation and air conditioning (HVAC) systems in health care facilities
  • CSA Z317.13-07 Infection control during construction, renovation and maintenance of health care facilities
  • Occupational Health and Safety Regulations, 2020 6-2
  • Occupational Health and Safety Regulations, 2020 6-3