[SC] Demystifying Portable Air Purifiers in Healthcare

Air purifiers (air scrubbers or portable HEPA filters) have attracted significant attention with hospitals, aged care facilities, office-based practices such as GPs and schools — all purchasing units to reduce transmission of harmful pathogens such as SARS-CoV-2.

But do they work? Will they protect our patients and healthcare workers from airborne viruses, and what are the considerations when choosing an air purifier for the healthcare setting?

An observational study published in Infection Control & Hospital Epidemiology¹, provides some insights into these questions. Set in a large Melbourne tertiary hospital, this study traced the airflow, transmission, and clearance of aerosolised particles within the clinical spaces to examine the impact of portable air purifiers.

Employing glycerin-based aerosol smoke as a surrogate for respiratory aerosols, researchers measured the movement from a single patient room into the corridor and nurses station within one ward. Rates of clearance were calculated without and then with the addition of portable HEPA filters.

Their baseline measurement demonstrated the rapid travel of aerosols from the patient room into both the corridor and nurse’s station. The addition of two portable HEPA air purifiers to a single patient room, with the door closed, resulted in 99% of aerosols being cleared within 5.5 minutes, equivalent to a 67% reduction compared with no air cleaners. The researchers concluded, “Air cleaners may be useful in clinical spaces to help reduce the risk of acquisition of respiratory viruses that are transmitted via aerosols. They are easy to deploy and are likely to be cost-effective in a variety of healthcare settings.”

Considerations for choosing an air purifier

Features and functions to consider when choosing an appropriate air filter can be confusing, as procurement and infection prevention teams come to terms with the language and norms associated with air purification systems. Ultimately, the filtering efficiency will depend on the air purifier’s power, filtering capacity, and the space volume in the room. However, many other aspects warrant consideration.

Filters

Ensure the unit contains genuine HEPA filters and not HEPA-like filters. HEPA stands for High Efficiency Particulate Air. HEPA H13 – H14 are considered medical-grade quality, filtering a minimum of 99.97% particles down to 0.3 microns in diameter.

The addition of pre-filters protect and prolong the life of the HEPA filters, and carbon or charcoal filters reduce unwanted odours and Volatile Organic Compounds (VOCs). Filters must be changed according to facility infection prevention policies, but an air purifier unit with a Change of Filter notification system will aid timely removal and replacement.

Clean Air Delivery Rate (CADR)

Expressed in cubic metres per hour (m³/hr), CADR is an industry-standard measure of the air volume that the air purifier can clean. The higher the number, the more effective. An air purifier with high and variable flow rate options will ensure adequate air changes/hour.

Particle sensor

Built-in particle or air quality sensors analyse air quality within the room. The amount of PM2.5 in the air is a key indicator of air quality. PM stands for particulate matter, and 2.5 refers to size (2.5 micrometres). As the unit cleans the air, the level of improvement can be observed using a numerical or colour-coded monitor function. Units with an auto-mode will adjust the speed of the motor automatically according to air quality.

PM2.5 Value	Less than 100	101–200	201–300	>300
Air Quality	Very good	Good	Not good	Bad

Airflow

Multiple and larger intake vents provide efficient air entry to the filtering system. Ensure inlets and outlet vents are unobstructed when placing the unit within a room.

Patient comfort

Noise levels, measured in decibels (dB), is a significant consideration when used in a patient room. Look for a product that provides both minimum and maximum noise levels, reflective of low or high fan settings. A night mode function cuts the lights and the noise to give patients a chance to rest and recover.

Ease of use, easy to clean

Are the pre-filters easy to remove and clean? Are the HEPA filters easy to replace? Look for a unit that can be easily moved around the room and placed in the most appropriate position. Outer surfaces should be easy to clean, and the device should come with cleaning instructions, including compatible disinfectants.

Additional questions to ask

This includes the availability of replacement filters, level of after-sales support, service packages and warranty. Does the manufacturer have experience and knowledge of the policy and procedural guidelines unique to infection prevention and healthcare organisations?

Cost, of course, is a consideration with any purchase. When reviewing over-all expenditure, include not only the critical functions mentioned above, but also the price of replacement filters, additional cost-saving measures such as pre-filters, auto-mode, etc. and the expected life span of the unit.

Reference

^{1 Buising KL, et al. (2021). Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019 (COVID-19) ward. Infection Control & Hospital Epidemiology, https://doi.org/10.1017/ice.202284.}