by Doug Rice and Mark Selawry

In days past, the onsite hotel IT person was a jack of all trades, knowing enough about each of the technologies to configure and support them reasonably well. Of course, the portfolio was probably just the property management system, point of sale, telephone system, entertainment system, and door locks. And of course, an interface computer to manage connectivity, usually by receiving, storing, and sending text files over serial interfaces.

The days when any one person can know every technology used in a modern hotel are now long past. And there is one emerging area that is becoming very important to hotels but that very few industry technologists, including me, know much about. I have wanted to write about it for a while but did not feel I could cover it competently – until now.

That issue is indoor air quality. It came to the forefront during COVID because of concerns about airborne transmission. However, its importance had been growing for years, with concerns about carbon dioxide (CO2), volatile organic compounds (VOCs), and particulate matter (PM). According to the Environmental Protection Agency, Americans spend approximately 90 percent of their time indoors, where concentrations of some pollutants can be two to five times higher than outdoors.

Many people suffer immediate physical reactions when exposed to pollutants in the air, ranging from headaches and nausea to sleeplessness and respiratory issues. Sick Building Syndrome affects some people when they enter a building; it diminishes when they leave. Long-term exposure to indoor pollutants can lead to chronic illnesses like cancer. Viruses and bacteria that are spread via the air, such as influenza, coronavirus, and legionella, can cause severe illness or even death.

Hotels regularly use cleaning supplies, paints, insecticides, and other products that introduce chemicals, including VOCs, into the building. Building materials, new furniture, and new carpets can emit toxins like formaldehyde and benzene. Mold and pet dander are common issues. Even water, outside air, and people coming into a building can be vectors of disease transmission, with people having come to the forefront during the current pandemic.

Ventilation in hotels is often both poor and poorly understood. You can approximate the quality of outdoor air by exchanging indoor and outdoor air about six times per hour, but in most climates that means a lot of energy is needed to heat or cool the incoming air. To reduce energy usage, heated or cooled outdoor air is typically mixed with existing indoor air. The exchange rate then drops to about twice an hour, meaning contaminants are removed only slowly.

Public awareness of air quality has increased dramatically on the back of the COVID epidemic because the virus is transmitted principally through the air. The indoor transmission rate has been estimated at 18.7 times higher than outdoors, where dilution occurs much faster. In the past 18 months, many businesses, schools, restaurants, and other facilities (including some hotels) have acquired and/or retrofitted various technologies to try to reduce the spread of viruses. I have been watching the space but was hesitant to cover it in depth because the technologies are complex; they are based more on biology, chemistry, and physics that I studied too long ago, and less on the bits and bytes I know. My understanding of the various sciences was not up to the task, especially as I saw many post-COVID product claims that were subsequently refuted by science.

Hotels were understandably skeptical about some of the technologies that appeared, with questions about safety, cost, effectiveness, and environmental side effects such as energy consumption and ozone emissions. There were conflicting reports on what levels of different pollutants were “safe,” and even how to measure them. And, perhaps most important, assuming a technology was safe, effective, and affordable, there was the ROI question. Would guests or staff be able to perceive any difference, and would it still matter post-pandemic? In other words, what is the sensible business decision for a hotel to make to improve guest and staff confidence without breaking the bank?

It seemed like a difficult subject to take on, so I was delighted when I was approached by an old industry colleague who has spent the last few years focused on healthy air and other wellness technologies. He had looked at the science and reviewed the technologies even pre-COVID. He knew some of the leading companies in the field, ones that help hospitals, nursing homes, and other high-risk facilities reduce their risk. He understands the technology enough to ask the right questions, which I knew I did not. And earlier in his career, Mark Selawry held senior level positions at Hilton and Carlson Rezidor, making him a fellow hotelier who understands the industry and its challenges. Mark generously offered to share his expertise and contacts by co-authoring this week’s blog with me. He was the principal contributor of the content in the remainder of the column, so I will now sit back and try to learn, along with you.

How We Gathered Information

For this article, we spoke with senior executives at several companies that had established reputations for reliable air-quality products that predated COVID, often by many years, and that have a history in demanding applications such as health care. Some of their products are mentioned here and are worth a deeper look in the pursuit of better air quality in hotels. To be sure, there are other companies, some of them quite good, but we chose a representative set with disruptive innovations that can serve as a useful point of comparison for similar products found elsewhere.

Many of the people we interviewed were among the most respected within the scientific and medical disinfection field, and they were generous with their time and knowledge. In addition to those quoted directly below, our sincere thanks to Fred Maxik (Chief Scientific Officer at Healthe Inc.), Julien Stamatakis (co-founder and CTO of Senseware) and his colleague Rose Khalife, and Todd Follmer (Director) and Bradley Balow (Vice President) at Aerus ActivePure, for sharing their thoughts and helping us better understand these complex technologies.

Measuring Air Quality

Hotels have long been understood as a potential vector of disease transmission. The Lancet, the primary medical journal in the United Kingdom, featured an article in 1895 (not a typo!) titled “Hotels and Infectious Diseases,” outlining the various ways diseases can be transmitted in hotels, including via air.
But what is good air quality, and how is it defined and measured? We intrinsically understand that “bad air quality” includes malodors often associated with the physical symptoms mentioned earlier. Many occupants of buildings with poor air quality simply do not feel well. They may also become more ill in response to viruses like COVID.

“Pathogenic load” and “contagion risk,” while important, are narrow facets defining air quality. Prior to the COVID epidemic, much research was focused on common air pollutants, including VOCs and CO2, and their impact on human health. The Harvard T.H. Chan School of Public Health estimated that poor indoor air quality resulted in a 10% decrease in cognitive ability. And The New York Times featured an article “Is Conference Room Air Making You Dumber?” that concluded “indoor air quality matters more than you think.”

Hoteliers are often unaware of how everyday decisions can harm their indoor air quality. The risk of harmful effects of pollutants and pathogenic microbes is reduced by dilution with fresh air, but this is contrary to trends that try to reduce our carbon footprint or save energy costs; fewer air exchanges lead to less need to heat or cool the incoming air.

Several governmental bodies have defined air-quality guidelines for various pollutants and density of microbes. Among these are the American Conference of Governmental Industrial Hygienists (ACGIH), which publishes Threshold Limit Values and Biological Exposure Indices (TLVs and BEIs). BEI is defined as “the maximum average airborne concentration of a hazardous material to which healthy adult workers can be exposed during an eight-hour workday and 40-hour workweek—over a working lifetime—without experiencing significant adverse health effects.” Similar standards exist for particulate matter (PM) levels. The outcome of this is that “good air quality,” by way of elimination, is well defined for common hazardous substances.

Interestingly, there are no similar “limit values” for pathogenic microbes, even though it is well known different pathogens require different loads (as defined by units per volume of air) to become contagious. We were told it takes only one tuberculosis bacterium to infect someone, while loads for other pathogens vary and are typically much higher. A zero load is not a realistic target in occupied spaces, so the focus has been on reducing risk of infection by reducing microbial load; for example, hospital grade reduction is defined as a 99.99% reduction in microbial count. The government approach in terms of managing risk is one of “dilution” and “filtration” for air quality, setting guidelines for minimum air exchanges, which can be achieved through a combination of improved ventilation and air treatment with mechanical filtration, for example.

Until recently, the Occupational Safety and Health Administration (OSHA) has always exempted pathogens like influenza, the common cold, and other viruses and bacteria from its regulations governing workplace hazards (and business’s liability for not actively managing them). However, it now considers COVID a workplace hazard and can impose stiff fines and heavy reporting paperwork to employers who cannot prove they are taking necessary steps to remediate COVID in the workplace.

Some products on the market produce an “air quality index” that purports to measure indoor air quality. However, the EPA version of such an index applies only to outside air; the nature of indoor air is different. Experts agreed that no single measure (index) of indoor air quality is appropriate; rather they recommend measuring concentrations of CO2, VOCs, and PM at a minimum.

Indoor Disease Transmission

In considering how to reduce the risk of airborne diseases in occupied spaces, it is useful to understand the transmission mechanism. SARS-CoV-2 viruses are encapsulated in a droplet of water exhaled from an infected individual. These droplets eventually fall to the floor, becoming a low risk; this is the basis for the recommended six-foot separation in occupied spaces. In low humidity environments, however, the encapsulating droplets can evaporate, releasing sub-micron particles to float, usually rising to the upper air of an occupied space together with warmer air. The SARS-CoV-2 virion is transmissible in both droplet and particle form; the latter, because of its small size, is harder to remediate.

Risk of transmission of coronavirus (and other respiratory contagions like influenza) can be somewhat reduced through operational practices, such as by minimizing human density and turnover in a space, or ensuring that people are not placed downstream from a ventilation duct. Air flow is key, so opening windows or doors to introduce outside air may be an option. Outside air is also disinfected by nature: ultraviolet (UV) waves from sunlight interact with water molecules and oxygen to produce free radicals, which either destroy pathogens or interfere with their ability to replicate. Some of these free radicals linger long enough to be effective if introduced indoors. The UV spectrum itself is effective in killing microbes. Thus, ventilation during a sunny day not only dilutes microbial load but directly reduces it.

We spoke with Bill Hayward, who developed the Hayward Score for residential areas; it was more recently expanded to restaurants and classrooms. Bill’s journey to promote clean indoor air resulted from his own personal health crisis. As a frequent business traveler, he became chemically intolerant of indoor air pollutants, suffering from insomnia and anxiety. Working with academics such as Professor Mark Hernandez of the University of Colorado, Bill promotes trying to replicate outdoor air quality indoors through a combination of ventilation and HEPA filtration. He says, “COVID has awakened us to what’s in our air – we’ll be more aware of this forever more.”

Improving Indoor Air Quality

For hotels to fully recover from the COVID crisis, they need to restore confidence of hesitant guests and staff to return. This requires a more aggressive approach than merely limiting occupant density and managing air flow. In all but a few climates, options for improved ventilation and outdoor dining are limited, so high-risk areas need to be addressed. These can include the front desk, buffet lines, meeting and conference areas, restrooms, elevator lobbies, fitness centers, and other areas where risk of transmission is highest. Fortunately, there are innovations available related to indoor air purification.

Fogging (the use of chemicals with electrostatic sprayers) and other interventions have been commonly used in many hotels in the past 18 months but are primarily useful in spaces (such as guest rooms) that are known to be infected. These can indeed reduce microbial load at the time of treatment, but do not offer the continuous protection required for public spaces where contagious people may interact with others at any time and without knowing it.

For this, one standard approach endorsed by many government and academic bodies across the world is to insert filters (HEPA or MERV-rated) into heating, ventilation and air conditioning (HVAC) systems. A HEPA filter is useful to remove particles as small as 0.3 microns. Specific to COVID, while that might work for the droplets mentioned above, it may not capture the smaller particles whose droplets have evaporated. The combination of these virions, especially in low-humidity environments, and air flow that may allow droplets to infect people before they fall to the ground or reach a filter, means that protection levels may be better than not filtering, but still not enough to prevent transmission. As well, HVAC systems with more aggressive filtration often run at 100% capacity, consuming more energy and incurring higher maintenance costs. To help mitigate the energy intensity of heavily filtered HVAC, Bill Hayward promotes adding energy recovery ventilation units such as those made by Ventacity.

A common technique used by major healthcare facilities involves chemical air purification devices. Some are combined with HEPA filters, and they can achieve 99.99% removal of viruses in lab tests. An example is ActivePure Medical Guardian device from Aerus, an FDA-cleared device with ActivePure technology. This uses a honeycomb chamber with a mineral oxide catalyst interacting with ultraviolet light with a specific wavelength that, unlike some, avoids creating ozone pollutants (in fact, the process consumes some).

Using the same method as occurs in nature when sunlight interacts with humidity in the air, free radicals (which the company calls ActivePure molecules) are produced. In turn, these can decompose pollutants into harmless particles, with the only by-products being three common molecules found in nature. Unlike filtration, this makes ActivePure an active intervention against pathogens and air pollutants, inactivating as opposed to merely trapping them. In lab tests, the product inactivated 99.99% of the SARS-CoV-2 virus in three minutes. However, the company notes that real-life installations are less controlled than laboratories, and therefore recommends before-and-after testing as part of its installation process.

Aerus produces many devices that incorporate ActivePure molecules, including standalone air purifiers, in-duct units, and in-ceiling units; they can be used in conjunction with filters. It reports a school district that was able to shift to lower-rated (8 vs. 13) MERV filters while still achieving a 70% to 80% improvement in air purity. The lower-rated and less expensive MERV filters allow significantly more air exchanges per hour, improving air quality further as well as reducing energy and maintenance costs.

Aerus described their design process, which is based on the total cubic feet of air in a space and the density of occupants; together, these define the relative risk of COVID transmission. Because small hotels have less space that tends to be densely occupied than large ones, costs (which are in the range of $1 to $2 per square foot) can be modest even for smaller properties.

Ultraviolet-C (UVC) technology is another option. The U.S. Food and Drug Administration (FDA) agrees that UVC radiation is a known disinfectant for air, and it has been effectively used for decades to reduce the spread of bacteria. It has also been shown to destroy the outer protein of the SARS Coronavirus (which is not the same as SARS-CoV-2), leading to its inactivation. The FDA says UVC may also be effective with SARS-CoV-2, but there is less published data to validate the wavelength, dose, and duration needed to deactivate it.

Healthe provides UVC lighting options that can be used to attack pathogens that escape filtration and enter the upper air. Unlike the earlier mercury-vapor lamp generation of UVC, Healthe now uses a specific (222 nm) wavelength in doses that attack virions but not larger particles; it can only penetrate about one micron into human cells, which is not enough to damage them. The lights can therefore be pointed down from the ceiling, vs. earlier technologies that could only target upper-air levels of a room. Those earlier generations had been tested over decades in schools and other environments and reduced contagion of various diseases by about 70%. Given the safety data that has been published on the newer technology, ACGIH (an independent organization that measures UV exposure for NIOSH and OSHA and sets regulatory thresholds) has recommended that the standards that were set decades ago for the 222nm UVC wavelength should now be increased to a level 17 times higher, so there may be significant room for further improvement.

Creation of ozone is another potential side effect of UVC technologies but occurs principally when the wavelength is below 200nm, so is not an issue with Healthe’s solution.

As with Aerus, Healthe assess the contagion risk of a given environment based on room dimensions and occupancy density, and tailors appropriate solutions. At $10 per square foot average, this technology is used more as a “spot” solution to manage the highest risk areas. Having said that, its design flexibility allows it to be installed in everything from banquet halls to buffet lines.

Another option, bipolar ionization, is also considered an “active” air disinfection process. It involves the production of ions as air passes between electrically charged plates. However, its efficacy has been questioned, and at least one major manufacturer is defending a class-action lawsuit that alleges it made false claims concerning the effectiveness of the technology.

Is There an ROI?

One of the biggest questions is whether and how hotels receive financial benefits from better air quality. While every hotel will have different considerations depending on factors like climate, existing ventilation, attitudes of guests and staff, and their difficulty in finding staff, there are case studies. We heard of several from the vendors we spoke with, covering hotels, restaurants, schools, hospitals, and prisons. But we will relate one from a hotelier, as it was the most persuasive.

The Post Ranch Inn, an iconic oceanfront hotel in Big Sur, California, invested a modest sum of about $30,000 post-COVID in several technologies, including in-duct and portable HEPA filters, energy recovery ventilation units, air quality monitors, and others. It focused principally on its fine-dining Sierra Mar Restaurant, and placed readouts from Senseware air-quality monitors where staff and guests could see them, including publishing them real-time via a link on the hotel’s website. The hotel was able to show that their indoor air quality was equivalent to and sometimes even better than outdoor air quality.

Mike Freed, the hotel’s owner, measured the payback on the investment as “three days,” based solely on incremental food and beverage spending in the restaurant. Many COVID-wary guests were immediately persuaded to abandon room service pizza or quick outdoor meals in the cold, in favor of full prix-fixe meals in the dining room with expensive wines.

He noted a second important benefit over time, perhaps just as important, which was that the staff felt safer – so much so that he was able to hire top staff away from other businesses at a time when many hotels were unable to hire anyone at all. Good air quality was one factor, but another was an Electro-Chemical Activation water unit from Annihilare, which makes an effective disinfecting solution onsite from nontoxic hypochlorous acid and sea water; this was a hit with the cleaning crew vs. traditional solutions like bleach and ammonia, especially since it does not require the use of gloves and masks.

While the food and beverage ROI would likely be lower for many hotels and might not be as significant post-COVID, the impact on staff could be replicated most anywhere. And the practice of publishing the air quality metrics where guests can see them could be a significant differentiator for any hotel, particularly in locations with poor outdoor air quality.


Indoor air quality matters to hotels trying to regain the confidence of guests and staff. While some potential actions can be expensive, many are not. The experts agreed that the right starting place is to get a professional review of the building’s current air quality and ventilation design, since some buildings may need very little remediation. For others, it will help owners focus on the areas of greatest concern and highest potential return. And if you have good air quality already, or can take actions to achieve it, be sure to make it visible to your guests and staff, as The Post Ranch Inn did!