In managing infection risk, the COVID-19 pandemic highlighted the centrality of indoor air. It is common for people to spend a significant amount of time in enclosed spaces, such as homes, workplaces, and schools. Maintaining the healthiness of indoor air, therefore, is a vital aspect of prevention initiatives. In this article, we will focus on the parameters that affect indoor air quality, describing various practices and intervention technologies.
Why Air Quality Matters Against Respiratory Viruses
Respiratory viruses, such as SARS-CoV-2 and influenza viruses, spread through the air from an infected individual who coughs, sneezes, or speaks. Pathogens are carried by relatively large particles known as droplets, and smaller particles classified as aerosols. The latter, specifically, remain suspended in the air for long periods, traveling distances greater than 2 meters. In enclosed and poorly ventilated spaces, this contributes to infection risk. In a confined environment, airborne viruses accumulate, reaching high concentrations. Potentially, these pathogens are inhaled by other occupants of the same environment, triggering infectious disease. In this context, the importance of ventilation stands out, as it allows for the dilution of viruses dispersed in bioaerosols if present and sufficient.
The Correlation Between Poor Ventilation and Infection Rates
To understand infectious dynamics, there are numerous investigations into the role of ventilation. According to a systematic review that examined 65 studies conducted until 2008, poor ventilation is associated with an increase in infection rates. Conversely, a higher air exchange rate can ensure greater dilution of suspended particles, reducing airborne infections. A third finding concludes that airflow can carry viruses to a point further from the source, provided the viral concentration is sufficiently high.
Other studies on the subject were developed post-pandemic. A specific investigation states that when the ventilation rate in a room is insufficient, infection risks related to viral transmission—both short and long distance—are high. Furthermore, the study highlights the need to re-evaluate this parameter when the physical distance between people is less than two meters.
Natural vs. Mechanical Ventilation: Pros, Cons, and Best Practices
Indoor air exchange is an integral part of effective prevention. This is made possible through ventilation, obtained either manually (naturally) or mechanically. Both methods have advantages and disadvantages.
- Natural Ventilation
Intuitively, manual or natural ventilation consists of simply opening windows. This allows potentially contaminated indoor air to exit and fresh outdoor air to enter.
It is an economical and easy-to-implement measure, although it can be uncomfortable in winter, sometimes discontinuous, and not always sufficient for high-traffic environments.
- Controlled Mechanical Ventilation (CMV)
Achieved with specific equipment, this method uses a system of fans and ducts. Among the associated benefits is the continuous activation of devices, allowing for constant air exchange. Positive aspects also include the possibility of enhancement through the integration of high-efficiency filters. Conversely, it is an expensive solution due to energy costs and requires regular maintenance.
When Manual Air Exchange Is Not Enough
Natural ventilation, while useful, has the limitations mentioned above. With the emergence of viral variants with high transmission capacity, this method is not suitable for crowded indoor spaces (e.g., university lecture halls, offices, etc.). In such environments, the viral presence can significantly outlast manual air exchange. In these contexts, it is important to supplement natural ventilation with other prevention strategies, such as mechanical systems and/or modern active air purification tools.
Beyond Ventilation: Integrating Active Inactivation Technology
Ventilation and filtration work by lowering the viral concentration in indoor air. However, they cannot inactivate residual pathogens. Today’s mitigation possibilities leverage technological progress, aiming for strategies that act actively to neutralize viruses.
e4life’s e4shield™ Technology: A New Paradigm in Biosecurity
Among the prominent measures is e4shield™, the technology developed by e4life. Using low-intensity electromagnetic waves, it is harmful to viruses in bioaerosols but harmless to people and animals. Devices designed with e4shield™ utilize the SRET phenomenon (Structure-Resonant Energy Transfer). Specifically, they emit an oscillating electromagnetic field that resonates with the outer envelope of the virus. As a direct result, the virus undergoes mechanical stress and is irreversibly damaged. The target virus is ultimately inactivated and no longer dangerous to the human host. Below are the advantages of the technology:
- Efficacy and Speed: Investigations by major scientific entities (including the Celio Military Polyclinic, the University of Milan, and the University of Genoa) have confirmed an inactivation efficacy exceeding 90-95% on known pathogens such as SARS-CoV-2 and influenza viruses. Regarding action times, linked to the speed of wave propagation, they are nearly instantaneous.
- Safety and Sustainability: e4life devices meet human and animal safety requirements, boasting CE and SAR certifications. Furthermore, the technology is sustainable, as it does not produce chemical by-products or components that need replacement/disposal.
- Complementarity: This measure is not intended to replace other intervention strategies but rather to integrate and enhance them. With its “protective cloud,” e4shield™ inactivates viruses that remain in bioaerosols due to insufficient ventilation.
Practical Indicators: CO₂, Relative Humidity, and Air Exchanges
Active mitigation of infection risk preferably requires continuous monitoring of indoor air health. Below, we describe the parameters to consider.
How to Interpret Data to Ensure a Healthy Environment
- Carbon Dioxide (CO₂): CO₂ is an important indicator of air quality. It comes from respiration and accumulates in indoor spaces when air exchange is poor. Specifically, a CO₂ value above 1000 ppm suggests insufficient ventilation, while levels between 800 and 1000 ppm are considered adequate.
- Relative Humidity (RH): Optimal control of this parameter aids in infection risk management. Values below 40% indicate excessively dry air, which can favor the suspension of aerosols and the viability of “enveloped” viruses (e.g., influenza virus, SARS-CoV-2). Other pathogens, on the other hand, resist values above 60%, as is the case with the common cold virus. An optimal level of relative humidity is between 40% and 60%, which also promotes respiratory health and defensive efficiency.
- Air Exchanges per Hour (ACH): This parameter refers to how many times the total air volume of an environment is replaced by outdoor air in one hour. For domestic environments, a value between 0.3 and 0.5 ACH is recommended.
Generally, there are devices capable of “sensing” these parameters in real-time and detecting when threshold values are exceeded. Modern devices are connected to ventilation and/or air purification systems that activate to restore acceptable values.
The Physics of Contagion: How Humidity Affects Droplet Range
The importance of humidity levels also translates into its effects on respiratory droplets. When released into the air by a potentially infected subject, these evaporate at a speed that depends on environmental humidity levels. Below is a brief description of the phenomenon:
- When indoor air is dry (RH < 40%): Evaporation is quite rapid. Droplets become smaller and lighter, staying in suspension longer and gaining higher travel capabilities. This increases the chances of viral transmission to healthy individuals in the same environment.
- When indoor air is humid (RH > 60%): Evaporation takes longer. Droplets “maintain” their structural and behavioral characteristics. In other words, they remain relatively large and heavy, settling quickly and at a short distance. This reduces the environmental spread of viruses.
The 40-60% relative humidity range is essentially a good compromise, hindering the viability of certain types of pathogens while also limiting the long-range spread of viable particles.
Strategies for the Home: Kitchen, Bedrooms, Bathroom, and Shared Spaces
Indoor air health must also be prioritized in domestic settings, especially during the cold season when living with infected family members is more likely. Here are some useful tips:
- Common Areas: It is good practice to encourage sufficient air exchange. Opening windows frequently and regularly in different areas of the home creates efficient cross-ventilation.
- Kitchen: Using stoves contributes to the accumulation of carbon dioxide and humidity. For this reason, it is preferable to keep the extractor hood on and ventilate the room multiple times.
- Bedrooms: Enclosed bedroom spaces need morning air exchange to expel CO₂ accumulated during the night and adjust humidity levels. When a family member is contagious, it is best for them to remain “isolated” in a single room, without neglecting frequent air exchange even in that circumstance.
- Bathroom: This environment is prone to excess humidity. It is therefore important to keep windows open to remove excess vapor or keep exhaust fans active.
Overall, it is possible to manage humidity levels with the help of humidifiers/dehumidifiers. Humidification is useful during cold months when heating systems tend to dry out the air. Dehumidification, in turn, is advantageous in the summer and/or when the climate is humid, to maintain an RH percentage below 60%.
Strategies for Offices and Shops: Layout, Filters, and Maintenance
While managing domestic spaces is relatively simple, the situation is more complex for workplaces and commercial areas where foot traffic is higher and continuous. An integrated approach is required in these environments.
- HVAC Enhancement: A first step is to upgrade Heating, Ventilation, and Air Conditioning (HVAC) systems. Generally, it is important to maintain filtration capabilities by integrating high-efficiency filters. Secondly, outdoor air intake should be set to the maximum allowed by the system. It is also preferable to keep ventilation running even when spaces are empty.
- Electromagnetic Wave Devices: Among the most suitable solutions for poorly ventilated spaces are e4life devices. Being harmless to occupants, these devices are ideal for offices, shops, and other high-traffic environments.
- Layout and Distancing: When possible, arrange workstations to allow for good interpersonal distance. Installing partitions can also partially hinder the spread of viruses in bioaerosols.
Managing Airflow to Avoid Viral Stagnation “Dead Zones”
In any indoor environment, “dead zones” can form—areas where air and respiratory droplets stagnate. To prevent or counter this, intervention in airflow is necessary. A primary aspect is the design of ventilation systems, which should be configured to allow clean air to enter from the side occupied by users and remove “stale” air from the opposite side. Another modifiable factor is the counterproductive use of desk fans; these favor the uncontrolled spread of environmental aerosols, bringing even settled particles back into suspension. To limit this phenomenon and encourage the exit of contaminants, fans should be directed toward an outdoor opening.
Maintenance Checklist: Ensuring Constant Effectiveness Over Time
Ventilation and/or purification systems maintain their efficiency only if properly maintained. Here are some indications provided by the Italian UNI EN 15780 standard.
- Filter Replacement: Clogged filters lose efficacy, impact energy consumption, and become a significant site for microbial proliferation. Therefore, they require regular checks and periodic replacement according to the manufacturer’s instructions.
- Cleaning Grilles and Vents: These components accumulate environmental debris, which has a notable impact on airflow. Periodic cleaning (e.g., every six months) is indispensable.
- Annual Overall Assessment: For optimal functioning, the general ventilation/filtration/purification system requires an annual check by specialized personnel.
- Duct Sanitization: If necessary, following the annual check, the entire system must undergo cleaning procedures to remove contaminants. Again, these operations are performed by qualified personnel.
Questions and Answers (FAQ)
How can I tell if I am ventilating enough?
Today, it is possible to use specific devices equipped with sensors that can detect when threshold values are exceeded. An important indicator, for example, is CO₂.
What is the ideal humidity?
In indoor spaces, an optimal relative humidity level is between 40% and 60%. This range limits the viability of various pathogenic species while supporting the natural defenses of the respiratory tract.
Doesn’t opening windows in winter lose too much heat?
Not necessarily. Opening windows frequently but for short periods (e.g., a few minutes) allows for good air exchange without significantly affecting accumulated heat.
Are air purifiers useful?
Purifiers equipped with high-efficiency filters (HEPA) capture virus-laden aerosols. They do not replace ventilation (natural or mechanical) but supplement it. Cutting-edge devices, such as those designed by e4life, actively neutralize viruses, providing an additional level of protection.
How often should systems be maintained?
Generally, you should follow the guidelines provided by the manufacturer. Additionally, annual inspections and potential cleaning by specialized personnel are important.
