Draft guidance on improving indoor air quality in office buildings: Indoor air quality and health

On this page

• Indoor air quality
• Summary of key strategies to improve air quality in office buildings
• Reducing airborne infectious aerosol exposure

Indoor air quality

Indoor air quality refers to the quality of the air in an indoor environment, such as inside a building, particularly as it relates to the health and comfort of occupants. Indoor air quality is the result of the constantly changing complex interactions among building systems, the environment around the building, activities and items in the building, and occupants that affect the types and levels of contaminants in indoor environments (CCIAQ 2013b).

Sources of indoor air contaminants

Contaminants found in the indoor air of a building can originate from sources within the buildings, can be affected by occupant behaviour, and can also be brought in from outdoors. Sources of indoor air contaminants include the following:

• Smoking or vaping
• Combustion sources (such as heating, cooking)
• Attached garages and parking facilities
• Building materials and office equipment (such as furniture, flooring, carpeting, cabinetry)
• Chemical products (such as consumer cleaning supplies, disinfectants, biocides)
• Consumer products (such as scents, printer emissions)
• Dampness and water leaks leading to mould growth
• Infiltration of outdoor air pollutants
• Infiltration of soil gases and radon
• Poor sanitation (such as dander from fur-bearing animals, dust, dirt, pest infestation)
• Occupants (such as exhaled carbon dioxide, bio effluents, viruses, bacteria)

Factors affecting indoor air quality

Indoor air quality is a result of the interaction of the ventilation system, the building, the climate, the quality of the outdoor air, indoor sources of air pollutants, the work processes, and the occupants.

Examples of some elements that impact indoor air include:

• improperly or inadequately designed, maintained or installed heating and ventilation systems. This can also apply to situations where these systems have not been properly modified to reflect building changes caused by renovations
• improperly or inadequately designed, maintained or installed building envelope or structure (such as water leaks through the roof, windows, walls, penetrations and flashings, as well as air leaks, which can lead to condensation, drafts, rodent or pest infestations, and sanitation issues)
• uses or activities that do not match the original design of the building or ventilation system (for example, there are more occupants than planned for in the ventilation system design)
• insufficient intake of outside air (such as resulting from an effort to improve energy efficiency) that may allow for a build-up of air contaminants indoors if there is insufficient exchange rate of the indoor air (such as how frequently indoor air is exhausted outdoors and replaced)
• the quality of the outdoor air drawn indoors
• the characteristics of the building or room (such as age, design, renovations, dimensions)
• the presence of certain building materials used in construction (such as asbestos-containing materials, lead, composite wood)
• the types of office equipment and furnishings present (such as emissions from photocopiers, off-gassing from furnishings, composite wood products containing formaldehyde)
• the permeation of contaminants into the building from the ground, such as radon or soil gases
• high humidity levels leading to increased odours, stuffiness, and potential for mould growth
• increased number of building occupants and time spent indoors; and
• occupant activities that impact air quality or circulation (such as placement of furnishings, renovations, blocking grilles or vents, cleaning spills, housekeeping, smoking, vaping) or items brought into the building (such as food, scented products).

Health effects of poor indoor air quality

In many cases, the presence of indoor air contaminants, including situations with poor temperature or humidity control, is known to cause health effects or make health effects worse. Exposure to indoor air contaminants may result in:

• dryness and irritation of the eyes, nose and throat
• respiratory symptoms such as wheezing, coughing and shortness of breath
• headache, fatigue, dizziness, nausea and flu-like symptoms
• worsening of lung and heart conditions such as asthma, chronic obstructive pulmonary disease (COPD), and heart disease.

Recognizing health effects that are being caused or exacerbated by exposure to poor IAQ can be difficult, as many of the symptoms can also be caused by illnesses or exposures unrelated to the air quality indoors. For example, exposure to poor IAQ has been associated with symptoms often experienced by individuals with allergies, the common cold or the flu (influenza), making it difficult to determine the role of IAQ in causing or worsening these symptoms (CCIAQ 2013c). As well, occupants who are exposed to and infected with a respiratory illness may experience symptoms similar to those experienced following exposure to other indoor air contaminants or may find that their symptoms are exacerbated when entering a building. A qualified health professional may be able to help determine whether an individual's symptom is associated with poor IAQ.

Poor IAQ does not affect everyone in the same way. Certain individuals are considered more susceptible to health effects associated with exposure to indoor air pollutants, including children, the elderly, people who are pregnant, and those with pre-existing health conditions such as asthma and cardiovascular diseases. Susceptible individuals may experience a variety of adverse health symptoms resulting from exposure to environmental pollutants, even at very low concentrations.

Occupant comfort and IAQ perception

An occupant's thermal comfort refers to conditions when an occupant feels neither too hot nor too cold when wearing a normal amount of clothing. An occupant's perception of IAQ may also influence their overall comfort, well-being and productivity. Occupant perceptions are influenced by factors such as air temperature, relative humidity, air movement and odour, as well as non-IAQ factors such as noise, lighting and ergonomics. Employers and building operators should consider both IAQ and non-IAQ factors when investigating IAQ complaints.

Air temperature and relative humidity

Air temperature and relative humidity are the two main factors that determine thermal comfort. Occupants find conditions most comfortable when the air temperature is uniform within a space with a relative humidity between 30% and 50%. Maintaining relative humidity in this range is important for preventing mould growth indoors (Health Canada 2016a).

Generally, when relative humidity is below 30%, complaints of dry skin, eyes, sinuses, mouth and throat increase. When relative humidity is above 50%, complaints of being too humid or warm increase. High humidity levels may contribute to condensation, moisture, and mould or fungi growth (Health Canada 2016d).

Personal preferences for temperature may vary greatly. When a space is too warm, occupants may feel lethargic or tire quickly. On the other hand, when the space is too cold, occupants may feel restless and easily distracted. The desired temperatures may vary with the season, clothing worn, and activity.

Odours

Odours (smells) can be indicative of elevated levels of certain pollutants in indoor air, which may lead to potential health risks, although for certain indoor pollutants, health effects are recognized to occur at levels below the odour threshold. Odours are also associated with a perception of poor air quality, regardless of whether or not the source of the odour is a nuisance concern (e.g., food odours) or has the potential to result in direct health effects (e.g., vehicle exhaust). Odours are often caused by organic or inorganic gases and vapours that stimulate the olfactory organs. Individual responses can vary with age, experience, time of exposure, and other factors.

Odours may be the result of:

• vehicle exhaust or other traffic pollution infiltrating into the occupied spaces of the building from outside or from parking garages
• body and food odours
• mould growth
• moisture (such as wet cement, dampness)
• chemicals and related vapours
• sewer gases
• pest infestation (such as rodents, bedbugs, cockroaches).

Identification and control of the odour's source will help improve IAQ. Note that personal or cultural factors or medical conditions can produce odours that may not be controlled by the individual. For response to environmental sensitivities and medical conditions, see employer's roles and responsibilities in Employers.

Ventilation and comfort

Indoor air contains a mixture of contaminants from both outdoor and indoor sources. When a building's ventilation system is designed and operated properly, it exchanges the indoor air by replacing or diluting it with outdoor air. This air exchange aims to keep the concentration of biological and chemical contaminants at low enough levels to not cause discomfort for most occupants.

When the rate of replacement of indoor air by outdoor air is too low, the indoor air concentrations of contaminants primarily produced indoors rise, and occupant complaints may become more common. Those complaints typically include exposure-related perceptions (such as smells/odours, "stale air," "stuffiness") and potential health effects (such as eye, nose, sinus and throat irritation, headaches, fatigue).

It is important to note that the addition of outdoor air into the system may also introduce contaminants into the indoor environment. Outdoor sources of contamination may include smoke, smog, traffic pollution, pollen and/or industrial contaminants. Increasing filtration within the existing ventilation system can often reduce the impact of outdoor sources on IAQ. See Outdoor air for more information regarding outdoor sources.

Air velocity and drafts

The air velocity (or speed) refers to the rate of air movement. Lower air velocities may make the space feel "stuffy," while high air velocities increase skin evaporation and may result in occupants finding the air too cool or "chilly." Air velocity should conform to standards set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) (ASHRAE 2020b). For normal buildings, an air velocity below 0.20 m/s (40 fpm) would be expected.

When there is an issue with the air velocity or leakiness in the building envelope, occupants may report drafts, experienced as an unwanted cooling of the body from air movement. Occupants note drafts when the air cools the body unevenly, such as at the head, neck, or shoulders or at the foot, ankle or lower leg. Drafts can be related to the air being 'thermally stratified,' which means there are layers of different air temperatures. Causes often include cold air entering through windows or walls, ventilation that directs "cold" air towards occupants, or floors that are colder than the air.

Non-IAQ factors

Concerns about the IAQ may occur even if all IAQ indicators are within acceptable limits. How an occupant perceives the general quality of air may depend on organizational and individual factors unrelated to the actual characteristics of the air. For example, noise, lighting, workplace layout, privacy and workstation design may contribute to how occupants perceive air quality.

Summary of key strategies to improve air quality in office buildings

The IAQ in an office building is the result of complex interactions that are constantly changing. As a result, addressing IAQ issues needs to consider many factors that often interact with each other. The following are key strategies to address some of these factors and to maintain and improve IAQ:

Reducing or eliminating the source(s) of air contaminants.

The source of the air pollutants may exist inside or outside the building. Detailed information on indoor pollutants is in Specific contaminants.

Examples of air contaminant sources that may originate from inside the building include:

• smoking or vaping
• heating systems and occupant activities (such as cooking and reheating food), which can produce combustion-related pollutants (such as carbon monoxide, nitrogen dioxide) and odours
• attached garages and parking facilities as a source of automotive and fuel-related pollutants (such as particulate matter, carbon monoxide, volatile and semi-volatile compounds)
• building materials and renovations (such as release of volatile and semi-volatile compounds and dusts/fibres from building materials, adhesives, cleaning products, furniture, paints)
• use of disinfectants and biocides beyond routine cleaning products to control microbial contaminants
• dampness and increased moisture leading to mould growth
• exhaled air of occupants, leading to increased carbon dioxide levels
• individuals with infectious diseases typically spread by respiratory aerosols and droplets
• perfumes, fragrances and air fresheners.

For indoor sources, contaminants can be eliminated or reduced by practicing good building stewardship, which includes adequate space design, choosing lower emitting products and furnishings, regular housekeeping, and preventative building maintenance, as well as through open communication between building operators and employers with building occupants (such as education of building staff and employees on IAQ).

Contaminants may also enter from outside the building through the outdoor air intakes of the ventilation system, open windows and doors, and by infiltration through cracks and openings in the building envelope. Examples of air contaminants that may originate from outside sources include:

• vehicle exhaust and other traffic related pollution (such as carbon monoxide, nitrogen oxide, particulate matter), including from vehicles idling near air intakes;
• nearby industrial contaminants;
• microbial contaminants (such as bacteria, mould, fungi, viruses, pollen)
• moisture and humidity leading to condensation and mould growth
• contaminants originating from shared ventilation systems with other businesses (such as in a shared building or strip mall)
• radon gas
• soil gases
• pollutants arising from environmental emergencies (such as fires, chemical spills).

The employer or building operator may have little control over contaminant sources originating from outside the building. However, awareness of outdoor air quality conditions, knowledge of the ventilation system, and good operation practices can help prevent or reduce the contaminants that may enter the building from outside sources. Other contaminants, such as radon, can also be reduced or eliminated through activities such as sealing foundation cracks, increasing ventilation, and remediation systems. See Radon for more information.

Ventilation

Ventilation can help improve air quality by removing and diluting contaminants and by replacing the indoor air with filtered air from outside. Maintaining the ventilation system in a building and replacing filters as per manufacturer's recommendations will help reduce contaminants drawn into the building.

Filtering and cleaning

Filtering and cleaning the indoor air can reduce some indoor air contaminants and some viral and bacterial respiratory pathogens, depending on the contaminants and filtration equipment used. Filtering the indoor air is rarely effective on its own and should be used alongside reducing contaminants at the source and improving ventilation. It is important to select the correct filter efficiency for the contaminants and the ventilation system present. The current public health recommendation is to use a filter with a minimum efficiency reporting value (MERV) rating of 13 or higher for recirculated air, when possible, in order to reduce viral transmission indoors (e.g., SARS-CoV-2 virus) along with improving IAQ overall (see Understanding HVAC systems for information on MERV ratings). Air cleaners (also known as air purifiers), particularly HEPA filters and electrostatic precipitators, can reduce levels of some air contaminants. It is important when choosing air cleaners to ensure that they do not produce ozone as a by-product, as ozone is harmful to your health (see Ozone for information). In general, when choosing an air purifier (Health Canada 2022a):

• look for a unit that is certified by a reputable organization, such as the Association of Home Appliance Manufacturers (AHAM)
• ensure the unit is appropriately sized for the room it will operate in, paying attention to the stated clean air delivery rate (CADR)
• install, position, operate and maintain the unit according to the manufacturer's recommendations.

For more detailed information on using ventilation and other control measures to address specific IAQ issues, please see Taking action.

Reducing airborne infectious aerosol exposure

Many of the same recommended control mechanisms that aim to improve and maintain good IAQ are also applicable when considering how to reduce the risk of infectious disease transmission. Ensuring proper ventilation by introducing outside air can reduce the concentration of contaminants - including virus - and bacteria - laden particles - in the indoor air, and are also dependent on the flow patterns, locations and activities being undertaken by persons that are infected. Proper ventilation can reduce surface contamination by removing some of the virus- and/or bacteria-laden particles before they can deposit on surfaces. When used alongside other individual public health measures (such as staying home when ill, wearing a well-fitting respirator or mask, practicing respirator etiquette and hand hygiene, cleaning and disinfecting surfaces and objects, and physical distancing), improving ventilation and air filtration can be part of a plan to reduce the spread of infectious diseases indoors (PHAC 2021a). For additional information on controlling exposure to infectious diseases, consult the Public Health Agency of Canada.