Humans can survive for 30 days without eating, 3 days without drinking, yet only 3 minutes without breathing. Of course our need for air is also constant, we rely on it at all times indoors and outdoors although can often be less clean than we would hope. Unpleasant odors make us aware of bad air, but many irritants and unhealthy gases are not easily detectable by smell while still affecting our health. Smells are the most obvious signal, as they are consciously perceived by the brain and nervous system, allowing us to make judgements about our environment.
Learn more about where poor indoor air quality comes from, why it's important to address within the built environment, and how to design for good indoor air quality and comfort.
Gases let off by compounds in a wide variety of modern products (paints, carpeting, flooring, furniture finishes, cosmetics, sprays, etc) have been shown to have a wide variety of detrimental effects on health - from interrupted attention and cognition to significant long-term health effects that include respiratory disorders and cancers. Sometimes, however, chemical and biological pollutants and other odor-free elements, even the stuffiness of a room, affect our health and comfort and cause headaches, fatigue, allergies, and other detrimental reactions.
While we’ve become well aware of the importance of outdoor air quality via news about smog-filled cities, we take for granted the air quality of indoor environments (particularly in buildings that make use of air conditioning). Unfortunately, very often indoor air is not clean either and can be doing us harm without our knowledge. Designers, however, are uniquely positioned to guarantee the quality of these working environments and eliminate that threat. Here’s what you need to know:
Indoor Air Quality, or IAQ, encompasses a variety of factors, including temperature, humidity, and concentration of pollutants. Generally, however, IAQ refers to the comfort, health, and well-being of building occupants. Accordingly, while pollutants and particles can be objectively measured, there is also a subjective component to IAQ. Factors such as age, gender, and even nationality and culture can affect the way an individual perceives air quality. The method of human perception of air quality is primarily through odors, as other types of sensory irritation require significantly more pollution to produce noticeable effects while still impacting health. However, even when not consciously recognized, poor air quality can have adverse effects on building occupants in the short- and long-term.
Why does it matter?
A building’s function, as well as its typical occupancy, can determine both the acceptable standards for indoor air quality and its possible consequences. For example, hospitals and schools both contain vulnerable populations and therefore the effects of poor air quality can be even more detrimental. Unacceptable air quality in a hospital can lead to patient infections and the spread of illnesses and affect the healthcare workers as well, decreasing their productivity and ability to provide effective care. Natural ventilation and daylight have also been shown to decrease recovery times and improve patients’ mental health [1, 2].
Similarly, in a school setting, poor IAQ can affect the students and staff. In students, poor air quality has been linked to greater absenteeism, aggravation of asthma and other respiratory illnesses, and decreased attention and productivity due to discomfort. Children are also likely to be more susceptible to environmental pollutants as their developing bodies breathe more air in proportion to their body size than adults. School staff, however, also feels the effects of poor air quality, leading to missed work days and possibly decreased teaching performance .
In a home or office, the influence of pollutants can be equally difficult to detect, as any symptoms can be challenging to identify and ascribe to a specific cause. Decreased focus and productivity are noted in office settings, where people also generally have less control over their indoor environment than they do in the home. High CO2 levels in an office building or poorly-ventilated meeting room can make workers feel tired and foggy, which can affect decision-making capabilities . If air quality in a home leads to stuffiness or other discomforts, it can affect sleep quality, as well as cause respiratory symptoms and headaches.
How do you measure it?
The sources of indoor air pollution can be classified into four categories. The ‘outdoor sources’ category includes traffic and industrial pollution. ‘Occupant-related activities and products’ encompasses pollution generated from things like cooking, tobacco smoke, cleaning products, personal care, and printers. The two building-related categories are ‘building materials and furnishings’ and ‘ventilation system components’. ‘Building materials and furnishings’ includes pollution from elements like plywood, paint, furniture, and floor or wall coverings, while ‘ventilation system components’ refers to filters, ducts, and humidifiers.
These sources can emit particles and/or gases that are intrinsic to the product itself, that are caused by the product coming into contact with other products, or that arise during use of the product. Such factors as the ventilation rate, air velocity, temperature, relative humidity, activities occurring in the space, and the frequency and duration of exposure to the pollutants influence the effects of these pollutants and the resultant perception of the indoor air quality.
To assess a building’s indoor air quality, considerations include the level of stuffiness, amount of gaseous pollutants and odors, and amount of particulate matter. The stuffiness of air is generally determined by measuring the level of CO2, while volatile organic compounds (VOCs) are measured to evaluate the level of pollutants. For example, the normal concentration of CO2 in outdoor air is between 250-350 ppm (parts per million), where a typical indoor space with a good air exchange ranges from 350-1,000 ppm. At upwards of 1,000 ppm, inhabitants may start to complain of drowsiness and poor air. When levels reach 2,000-5,000 ppm, the air feels noticeably stale, stagnant, and stuffy and can cause headaches, sleepiness, poor concentration, loss of attention, and even increased heart rate and slight nausea. The workplace exposure limit in most jurisdictions is 5,000 ppm for an 8 hour period. Also, VOC levels are commonly 2-5 times greater indoors than outdoors due to the many household products that release these chemicals.
Measuring the amount of particles in the air includes both “respirable suspended particles” and “fine particles,” which refer to two different sizes of particulates and the respective levels at which they cause discomfort and health implications. The larger particles (smaller than 10 micrometers) are dangerous at a level of 20 micrometers per cubic meter. Particles under 2.5 micrometers should not exceed 10 micrometers per cubic meter and are used to determine the air quality indexes commonly seen in large cities. Haze and smog are caused primarily by these smaller particles and are visual evidence of poor air quality in the outside air. Indoors, the most readily noticeable determinant of air quality is the odor. Assessing odors, however, is somewhat more subjective than the other measurements as it involves analysis of not only their concentration and intensity, but also their hedonic assessment (whether the odors are considered pleasant or unpleasant).
How to design for good Indoor Air Quality:
In harsher climates, often the approach is to make the building as impervious to the outdoors as possible. But the insulation and air-tightness can trap pollutants inside the building and lead to poor IAQ, which increases the importance of a good ventilation system. Ventilation systems can utilize natural ventilation, mechanical ventilation, or a hybrid of both. The key features of a ventilation system, as it relates to air quality, are sufficiently high air-change frequency and clean air supplied to the right places.
In a mechanical ventilation system, either automatic or manual detectors may be utilized to determine when ventilation is needed in a space. Automated systems can be set to a timer or programmed to detect pollutants levels, such as CO2, and are the most efficient option. However, manual control can increase the occupants’ perception of comfort. Another important human factor in mechanical systems is maintenance and upkeep. Even the best-designed (and built) ventilation system will not function as intended if not regularly maintained, for example if the air filters are not regularly changed.
Another option is natural ventilation, which eliminates costly mechanical equipment and ductwork from a project while also providing lower running costs. Building inhabitants enjoy the psychological benefits of contact with nature. By nature, however, natural ventilation is not controlled and therefore may not always be sufficient. Many locations, climates, and building types also create additional challenges to relying entirely on natural ventilation, primarily due to outdoor air and noise pollution and extreme indoor/outdoor temperature differences.
Many systems today incorporate both natural and mechanical ventilation aspects and are therefore considered hybrid systems. Today’s sustainability certification programs recognize the importance of IAQ and fresh air and have incorporated it into their specifications. Under UK program BREEAM, within the category of Health and Wellbeing, credits are available for minimizing sources of air pollution as well as providing potential for natural ventilation. The U.S. Green Building Council’s LEED program also awards points for designing for good air quality, but not specifically for natural ventilation. The WELL Building Standard takes a more holistic approach to indoor air quality, with “Air” as one of its seven core concepts and dozens of “features” that can be verified, from a smoking ban to cleaning protocol and humidity control.
Systems like these hint at the directions that architects and designers can take to provide buildings with healthy air. The encompassing strategy and best practice to improve indoor air quality is to reduce pollution at its source while also improving ventilation and purifying the air. A solid starting point is to carefully specify non-polluting materials and equipment to eliminate VOCs as much as possible, yet various mitigating factors can make this impractical or even unfeasible.
The next step, then, is ventilation and ensuring an adequate number of air changes per hour are provided to accommodate the volume of space. The number of air changes will be affected by factors like occupancy and activity in the space. As this air comes into the building, it should be purified, filtering out particulate matter. This is the time at which human attention becomes especially important, as if these filters are not maintained often, they can themselves become a source of pollution.
Another strategy is to incorporate plants into a building design, such as through a green wall or indoor planting area. Plants not only filter carbon dioxide and possibly some harmful chemicals out of the air, but the principles of biophilia posit that for humans to be in contact with nature increases mental and physical well-being. Plants alone, however, cannot solve a building’s air quality problems. Air purifying building products, like those in Activ’Air family, can also improve IAQ by absorbing formaldehyde from the air.
Air pollution is today’s most prevalent environmental killer, especially in developing countries, with approximately 7 million deaths annually worldwide. New construction has the opportunity to design for good indoor air quality, but many older buildings, or simply those built without concern for IAQ, would also benefit immensely from retrofitting to improve the indoor environment. We spend the majority of our time indoors, making it worth the effort and investment to ensure the very air we breathe is not causing us harm.
Note: This article was originally published on May 16, 2019 and updated on March 25, 2020.
-  https://www.healthdesign.org/chd/research/impact-light-outcomes-healthcare-settings
-  https://www.epa.gov/iaq-schools
-  Satish U, Mendell MJ, Shekhar K, Hotchi T, Sullivan D, Streufert S, Fisk WJ. Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environmental Health Perspectives, 2012, 120(12): 1671-1677
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