Home / Blog / Draft guidance on improving indoor air quality in office buildings: For professionals

Draft guidance on improving indoor air quality in office buildings: For professionals

May 15, 2023May 15, 2023

Indoor air quality professionals may include industrial or occupational hygienists, public health or medical professionals, environmental consultants, or other professionals that have an understanding of IAQ along with the training and equipment to investigate more detailed air quality issues, such as HVAC ventilation systems and building envelope issues. While the following information is intended for IAQ professionals, building operators or employers may find this information valuable to expand their understanding of the health effects of specific indoor air contaminants and of air sampling and monitoring.

This section reviews specific contaminants relating to IAQ in terms of their characteristics, health effects, and exposure limits and suggests methods to manage the issue. When considering indoor air contaminants, measuring the concentration of exposure may be warranted, depending on the issue.

Note: There may be occupational exposure limits (OELs) for certain contaminants that are regulated provincially and territorially, as well as federally for workers under federal jurisdiction, but they are generally not intended to be used for most office-only settings (ASHRAE 2009). An OEL is the level of admissible exposure for a length of time (usually 8 hours) to a chemical or physical hazard that is not likely to affect the health of a worker (CCOHS 2022). Certain workers (such as janitorial and maintenance staff) may be required to work with hazardous materials, in which case OELs would be relevant.

Health Canada has developed recommended health-based exposure limits for a number of pollutants commonly found in indoor air. These exposure limits are designed to be protective of populations considered susceptible to health effects resulting from pollutant exposure (such as children, the elderly, and those with pre-existing health conditions).

Health Canada's Residential Indoor Air Quality Guidelines (RIAQG) for indoor air pollutants include short- and/or long-term exposure limits, a summary of the known health effects, sources and exposure levels in Canadian homes, and recommendations to reduce exposure. While the RIAQG were developed for use in residential environments, exposure levels can be similar to those found in office environments, and people can routinely spend as much time in the office as they do at home, suggesting that the guidelines are applicable to office environments as well.

The RIAQG exposure limits represent the concentration of indoor air contaminants below which health effects are unlikely to occur, based on available scientific evidence. These exposure limits are reported alongside their recommended sampling times (in brackets). The guidelines include:

To assist public health professionals, including those involved in standards development processes, who may need to assess the risk from exposure to other VOCs potentially found in indoor air, Health Canada has developed screening values called Indoor Air Reference Levels (IARLs) . The IARLs supplement Health Canada's RIAQG and represent concentrations that are associated with acceptable levels of risk after long-term exposure (over several months or years) for specific VOCs commonly found in indoor air.

The information below on specific contaminants is up to date as of November 2022. Indoor air quality professionals are invited to consult Health Canada's indoor air quality resources for professionals webpage for the most up to date information on RIAQGs or IARLs.

See Employers for more details about the employer's responsibilities and duties. In all cases, consult with the applicable jurisdiction to confirm what legislation applies in the situation. The best approach is to always keep exposures or the risk of a hazard as low as possible (CCOHS 2022).

Carbon monoxide (CO) is a tasteless, odourless and colourless gas at room temperature. Carbon monoxide is usually formed during the incomplete combustion of organic materials. It is produced when fuel like coal, gasoline, natural gas, oil, propane, wood or wood pellets is burned. It is also a product of second-hand smoke. The risk is greatest in winter months when buildings are heated by:

These devices can release CO into a building if they are not installed or maintained correctly, or if they malfunction (Health Canada 2016b; 2017b).

Breathing CO reduces the body's ability to carry oxygen in the blood and can affect an individual before they notice its presence. Exposure to the gas can cause CO poisoning.

Exposure to CO can cause flu-like symptoms, even at levels lower than those which would trigger an alarm signal from a traditional alarm. Symptoms can include:

At increased levels, or if exposed to low levels for longer periods of time, people can experience:

At very high levels, it can cause:

Health Canada's RIAQG for CO (2016b) recommends the following:

Identify elevated levels of CO:

Install CO alarms or alarming systems throughout the building, including where CO could potentially be generated. Make sure that CO alarms are installed, calibrated, tested, used, maintained and replaced according to the manufacturer's specifications (Health Canada 2016b; 2017b).

Note on CO alarms:

To prevent CO exposure, do the following:

Carbon dioxide (CO2) is an odourless, colourless and non-flammable gas. Indoors, CO2 is mainly produced through the respiration of occupants, but it can also originate from other sources, such as unvented or poorly vented fuel-burning appliances and cigarette smoke. The level of CO2 in indoor air is a function of the following three main factors: the outdoor CO2 concentration, indoor sources of CO2, and the rate of removal or dilution of indoor CO2 with outdoor air by ventilation (Health Canada 2021g).

As ventilation is the primary means of removing CO2 from indoor environments, poorly ventilated buildings or buildings with unvented or poorly vented fuel-burning appliances may have elevated CO2 concentrations, especially if there is increased occupancy with respect to the size of the space (Health Canada 2021g).

Studies in humans in school or office settings have found associations between CO2 exposure and mucous membrane or lower respiratory system symptoms, rhinitis, neurophysiological symptoms, lack of concentration, headaches, dizziness, heavy-headedness, tiredness and decreased performance on tests or tasks.

Epidemiological studies looking at CO2 concentrations and health effects in school or office environments showed that individuals exposed to CO2 concentrations greater than 800 ppm were more likely to report mucous membrane or respiratory symptoms (such as eye irritation, sore or dry throat, stuffy, congested or runny nose, sneezing, and coughing) than people exposed to lower CO2 levels (Health Canada 2021g).

For indoor environments, Health Canada's RIAQG includes a long-term exposure limit (24 hours) of:

Manage the risks of exposure to CO2 by doing the following (Health Canada 2021g):

Ozone is a naturally occurring gas that is present in the upper atmosphere and can be formed at ground level when sunlight interacts with air pollution. Ground-level ozone is a key component in urban smog. Ground-level ozone can enter buildings and contaminate indoor air (Health Canada 2021d). There can also be indoor sources such as photocopiers and some air-cleaning devices (which can include electrostatic precipitators, certain ultraviolet generators, portable air purifiers, and devices used in remediation projects such as smoke damage restoration).

Exposure to ozone can cause a variety of health effects, including:

Individuals may be more sensitive to ozone if they have an underlying breathing condition.

For residential indoor environments, Health Canada (2016c) recommends:

Exposure to ozone can be reduced by doing the following:

Particulate matter that is present indoors consists of a mixture of substances, such as (Health Canada 2012; 2019a):

Common indoor sources of fine PM include:

Other sources of indoor fine particulate matter (PM2.5) include:

Particle size determines whether particulates can reach the lungs. Dust particulates are measured in microns or micrometres (µm). Fine particulate matter is a general term for small particles that measure less than 2.5 µm in size. Particles ranging from 0.1 to 2.5 µm can enter the lungs, which may affect health. Typically, particulates greater than 10 µm get trapped in the nose and throat (Health Canada 2012; 2019a).

While a small number of studies have investigated the relationship between indoor PM2.5 and health, the vast majority of health effect data comes from studies investigating exposure to outdoor (ambient) PM2.5. There is some evidence for a relationship between indoor PM 2.5 levels and decline in lung function and increases in exhaled nitric oxide, a marker of airway inflammation, in asthmatic children.

Associations between indoor PM2.5 and subtle changes in markers of cardiovascular disease have also been observed in older adults (Health Canada 2012; 2019a).

Health Canada (2012; 2019a) recommends keeping indoor levels of PM 2.5 as low as possible.

The main strategies to lower indoor levels of particulates include:

Volatile organic compounds are a large group of chemicals that are present in indoor and outdoor air. Exposure to certain VOCs commonly found in indoor air may affect your health, depending on which VOCs are present, the levels of VOCs present, and how long you are exposed (Health Canada 2021h).

Some common examples include:

Short-term exposure to high levels of some VOCs can cause:

Certain populations are considered more susceptible to health effects resulting from VOC exposure, including children, the elderly, pregnant people, and people with pre-existing health conditions such as asthma.

Most people are not affected by short-term exposure to the low levels of VOCs typically found in homes or offices. For long-term exposure to low levels of VOCs, research is ongoing to better understand any health effects.

Long-term exposure to high levels of some VOCs, however, may result in health effects. For example, in industrial workers, exposure to high levels of some VOCs has been linked with increased cancer rates. These VOCs include:

At the low levels typically found in offices, however, there is a negligible risk of developing cancer from both benzene and formaldehyde.

The following are Health Canada's RIAQG for specific VOCs commonly found in indoor air:

The following are Health Canada's IARLs for specific VOCs that may be found in indoor air (Health Canada 2018b). These values are for chronic, continuous long-term exposures.

The main strategies to reduce exposure to VOCs in an office include (Health Canada 2021h):

If there are people in the office who are more sensitive, they should:

Mould is the common word for any fungus that grows on food or damp building materials. It often looks like a stain and can come in a variety of colours. In some cases, however, mould may not be in a location where it can be seen, although there may be a musty odour. If it is present in significant enough quantities, mould can contribute to poor IAQ.

Damp or wet areas in the home or office caused by water leaks, flooding or high humidity can promote mould growth. Mould can grow on wood, paper, fabrics, drywall and insulation. It can also hide inside walls or above ceiling tiles. To grow, mould needs a damp place. Where there is mould amplification inside a building, it can contribute to poor IAQ and lead to health problems (Health Canada 2016d).

People living in homes or working in offices with mould and damp conditions are more likely to have:

Some people are more vulnerable to the effects of mould than others. These individuals may include children, seniors, and people with medical conditions (like asthma and severe allergies). Since some people are more sensitive than others, it is problematic to try to establish "safe" limits for mould in indoor air that could practically be used in a building.

Some airborne moulds can cause severe lung infections in people with very weakened immune systems (like those with leukemia or AIDS, or transplant recipients) (Health Canada 2021c).

There are no exposure limits for moulds present in air or on surfaces in buildings.

Mould is a natural part of the environment and will always be present, and simply finding mould spores in an air test does not necessarily indicate there is an issue (CCIAQ 2015). Considerable expertise is required to correctly interpret air sampling results, and such sampling may or may not be reflective of the presence or absence of a problem, due to limitations in air sampling and the highly variable nature of mould levels in air.

The results of air sampling cannot be interpreted regarding health risk and typically are of little to no value in developing a remediation plan to rectify a mould problem in a building. For this reason, Health Canada does not have a numerical health-based exposure limit for mould in the indoor environment (Health Canada 2016d).

Consequently, neither Health Canada nor the National Institute for Occupational Safety and Health (NIOSH) recommend testing for mould or similar substances in offices, schools or non-industrial buildings (Health Canada 2016d; NIOSH 2022).

Although sampling has been reported as part of a pre- and post-remediation quality-assurance strategy (CCIAQ 2015), the most important steps for determining the success of a mould remediation project include:

Health Canada recommends controlling dampness indoors and cleaning sources or surfaces.

Prevent any reoccurrence by inspecting for conditions that lead to the growth of microbials (Health Canada 2014a; 2016d). For smaller office buildings or smaller-scale mould problems, prevention activities that may be relevant include the following:

Specific diseases can be related to microbes, including Legionnaire's disease (from exposure to Legionella bacteria in HVAC water systems) and inflammatory responses following exposure to endotoxins produced by Gram-negative bacteria in some humidification systems. Other diseases include hantavirus pulmonary syndrome (from exposure to urine, saliva or droppings of infected deer mice and some other wild rodents when cleaning) and psittacosis (which is a bacterial disease contracted from exposure to inhaled dust from dried bird droppings). Diseases caused by exposure to aerosolized bird and bat feces and that can impact the indoor environment include histoplasmosis and aspergillosis. This emphasizes the importance of keeping air-handling units free of such contamination and preventing birds and bats from roosting in buildings.

There are also diseases that can originate from the occupants in the building (such as SARS-CoV-2 virus infection leading to COVID-19 disease and other respiratory pathogens like influenza). In most cases, transmission of a bacterial or viral infection between people will require contact with an infected individual or surface, the ability of the pathogen to be transmitted via aerosols or droplets, and/or a significant amount of virus- or bacteria-laden particles within the individual's direct breathing zone. However, with the SARS-CoV-2 virus, airborne transmission was also found to occur from fine aerosolized particles, which were able to remain suspended in air and travel further distances, hence the benefit of wearing masks, effective ventilation, improving building filtration, and adding stand-alone HEPA air purifiers when and where appropriate to reduce the risk of transmission.

The health effects will be specific to the particular agent of concern.

There are no exposure limits for the range of microbial agents found indoors that can cause disease as these are dependent on the infectious dose needed to cause an infection.

Many of the recommendations that apply to managing mould concerns (see Moulds) will apply to bacteria, viruses and pathogenic fungi. Hygienic operation of any HVAC system is important to ensure delivery of clean air, removal of contaminated indoor air, and prevention of conditions that will allow microbes to grow within the HVAC and cooling systems of the building (CCIAQ 2013d).

The most effective way to prevent excessive Legionella growth in the water of HVAC evaporative cooling towers is proper maintenance and operation of the water coolant systems, especially during spring and summer. This includes regular testing of the cooling tower water and the use of disinfectants (ASHRAE 2020a, ESDC 2018). A water-management program can be used to establish, track and improve operation and maintenance activities (CDC 2021). Culture and polymerase chain reaction methods are the most commonly used methods to test for Legionella in cooling towers and evaporative condensers. Some test methods may be performed on-site by the user or a qualified technician, while other methods may require contracting with a commercial laboratory. Regular testing can be used to confirm the effectiveness of Legionella control activities and identify when further actions (such as maintenance) may be necessary.

The importance of effective ventilation has been identified for reduction in viral transmission indoors (PSAC 2021c, 2022; CCIAQ 2021). Good ventilation for reducing viral transmission includes:

Ventilation can help reduce viral transmission in indoor spaces by preventing the accumulation of potentially infectious respiratory particles in the air. Good ventilation, combined with other individual public health measures, can further help reduce the risk of infection.

In addition to improving indoor ventilation, consider the following:

Asbestos comprises a group of six different types of minerals. These minerals have been used to increase the durability and strength of certain products or increase their fire-resistance (Health Canada 2021a). Before 1990, asbestos was commonly used for insulating buildings and homes against cold weather and noise. It was also used for fireproofing steel structural elements in buildings. Industry, construction and commercial sectors have used asbestos in products such as:

There are no significant health risks if materials containing asbestos in a building are left undisturbed and in a location where they would not be disturbed (such as being sealed behind walls and floorboards), and/or are tightly bound in products that are in good condition (such as cement piping or vinyl floor tiles).

An asbestos-management plan is a critical part of preventing exposure to any remaining ACM in a building. The plan should include strict requirements for containing or isolating such materials before entering spaces where they are contained. Contractors and building occupants must be made aware of such requirements prior to accessing any spaces containing these materials, in accordance with applicable legislation.

Breathing in asbestos fibres can cause cancer and other diseases, such as (Health Canada 2021a):

Federal, provincial and territorial occupational health and safety agencies are responsible for setting workplace limits for exposure to hazardous substances, as well as any asbestos-management plans for safe removal. Subsections 14.1(1) and (2) of the Hazardous Products Act, which Health Canada administers, prohibits the sale or importation of hazardous products that contain asbestos and that are intended for use, handling or storage in a workplace in Canada unless the applicable labelling and SDS requirements of the Hazardous Products Regulations are met. Occupational health and safety legislation also requires employers to inform and train their workers on the safe handling of hazardous products (Health Canada 2021a).

Reduce the risk of exposure by hiring a professional to test for asbestos before doing any:

If a professional finds asbestos, hire a qualified asbestos-removal specialist to safely get rid of it before beginning work in accordance with applicable regulations, which require asbestos be contained during removal to prevent the spread of the contamination. In some situations, it may be allowable to encapsulate the asbestos or isolate it to avoid disturbing the ACM (Health Canada 2021a).

There are occupational health and safety regulatory requirements in most jurisdictions to maintain an asbestos inventory and conduct regular inspections of ACM. Reporting procedures should also be established for workers to note any damage to ACM in the workplace.

Do not attempt to remove asbestos or suspected asbestos, unless it is done by a certified asbestos-removal professional who is following the criteria for asbestos abatement and removal. In some jurisdictions (such as Manitoba, Ontario, Quebec and New Brunswick), working with asbestos is closely regulated.

Radon is a radioactive gas that comes from the breakdown of uranium in soil and rock. It is invisible, odourless and tasteless. When radon is released from the ground into the outdoor air, it is diluted and is not an issue. However, in enclosed spaces like buildings, it can accumulate to high concentration levels and become a health risk. In geographical areas in which radon is present, it can enter a building through any opening where the building contacts the ground: cracks in foundation floor and walls, construction joints, gaps around service pipes, support posts, window casements, floor drains, sumps, or cavities inside walls (Health Canada 2021e).

Radon exposure is the number one cause of lung cancer in non-smokers, with 16% of lung cancers estimated to be from radon exposure, resulting in more than 3,000 lung cancer deaths in Canada each year (Health Canada 2019b). People who smoke and are exposed to radon have an even higher risk of lung cancer.

The health risk from radon is long-term, not immediate. The longer the exposure to high levels of radon, the greater the risk (Health Canada 2019b).

The exposure guideline established by Health Canada (2020) for radon in public buildings is 200 Bq/m3.

To find out whether radon is present in a building, a test must be conducted for radon levels. Measure indoor radon levels through a long-term sampling plan of at least 3 months, preferably during the winter months. Use radon measurement devices as recommended by Health Canada (Health Canada 2021e).

Health Canada, working with experts in the field of radon mitigation, created a guide to provide professional (qualified) building contractors with information on techniques for reducing radon levels in buildings in contact with soil. Please see the guide "Reducing Radon Levels in Existing Homes: A Canadian Guide for Professional Contractors" (Health Canada 2010).

If radon is detected in the building, workplaces must:

Air sampling consists of using specialized equipment to determine the level of a contaminant in the air.

In most cases, the only contaminants that should be sampled or consistently monitored in office buildings and other indoor environments are radon and carbon monoxide, respectively.

Air sampling of other indoor air pollutants should only be conducted by a qualified professional. Air sampling can be complicated and expensive and can generate results that are difficult to interpret. Therefore, careful consideration should be given to whether there is a need for measuring specific air pollutant levels to support the IAQ assessment or investigation. In some cases, it may be needed to be sure of regulatory compliance or to help further define the issue.

Sampling methods are specifically defined by agencies such as NIOSH and the US Environmental Protection Agency. They must be properly followed to make sure the results are valid.

While sampling has its applications, in most cases the focus should be on addressing sources and improving ventilation.

Air sampling can be used to:

Air sampling results are interpreted and compared to exposure limits or guidelines, where available.

Indoor air is a complex mixture of components and factors. There is no one simple measurement or factor that can easily establish if the IAQ is acceptable.

Most sampling methods are designed to detect a specific contaminant only. Knowledge of possible contaminants is required before testing begins to ensure the correct method is used.

Many indoor air contaminants are present at very low concentrations. A chosen sampling method may not be sensitive enough to accurately detect the contaminant of interest if it is present at a concentration below the detection limit. There are also numerous different possible contaminants to sample for. Knowing which to sample for may not be clear, and most have no guidelines or standards to facilitate the interpretation of results. It is possible for air sampling or monitoring in a complaint investigation to indicate that there are no IAQ issues even though the occupants are reporting health effects that they may be attributing to poor IAQ. Air sampling or monitoring, even when a professional conducts it and interprets the results, cannot be used to support or definitively rule out IAQ as the cause of adverse health effects experienced by occupants.

Many IAQ issues can be addressed without the use of air sampling. In most situations, identifying the potential sources of indoor air contaminants and taking measures to reduce these sources is more informative, cost effective, and health protective than testing the air.

Before sampling, use the results from walkthroughs, assessments, occupant surveys, building inspections and operational log reviews to help provide guidance to determine if sampling is required or if the results will be informative.

All air sampling should be conducted by qualified professionals in accordance with the legislation that applies to the jurisdiction of operation and the most current sampling methodology. The Institut de recherche Robert-Sauvé en santé et sécurité (IRSST) (2013) offers a Sampling Guide for Air Contaminants in the Workplace that is a helpful resource when determining the most appropriate sampling method for the contaminant. When you opt to perform air sampling, the following factors will help ensure that meaningful results are obtained:

An occupational hygienist, or other qualified individual, will develop a sampling strategy (if needed), working collaboratively with the employer and occupants to determine the best method for conducting sampling. Internal resources may be used to conduct the sampling where appropriate resources and equipment are available; however, external consultants and resources may be required.

Occupants working in the area may be notified before the sampling is conducted. It is important that workers co-operate with the sampling and do not intentionally or unintentionally contaminate collected samples. The person conducting the sampling should observe and monitor the equipment or otherwise ensure it is not tampered with during the sampling period to make sure it is operating correctly and has not been disturbed.

For sampling techniques that require the use of an external laboratory for analysis, only laboratories that follow an approved lab-accreditation program such as the National Voluntary Laboratory Accreditation Program (NVLAP), American Industrial Hygiene Association Laboratory Accreditation Programs (AIHA-LAP) or the Canadian Association for the Environmental Analytical Laboratories (CAEAL) should be used. The laboratory needs to be certified for the individual parameters to be analyzed, and appropriate chain of custody procedures must be followed.

There is no one method or instrument that will provide an indication of IAQ. All instruments must be maintained, calibrated and repaired according to manufacturer's instructions.

The following section illustrates some of the sampling parameters and the measurement instruments available. This not an exhaustive list of all air-sampling technologies for IAQ applications. It is provided as an example of some of the measurement techniques available to assess indoor air contaminants.

Psychrometers: measure the relative humidity using the temperature difference between two sensors, one of which is moist and cooled by air. Available as sling or powered instruments.

Hygrometers: use a sensor to measure resistance or capacitance as humidity varies.

Smoke tubes: a smoke diffuser produces a visible vapour that can indicate air movement (such as direction and speed). These are generally not used in occupied buildings to avoid exposing occupants to the smoke.

Thermal anemometers: sensors provide a direct readout of air velocity.

Thermal comfort (environmental) meters: sensors measure radiant temperature, air temperature, humidity and air motion.

Direct reading monitors: use a variety of technologies and chemical properties unique to each compound. Some gas monitors may incorporate an air pump or rely in the passive diffusion of gas across a sensor element.

Direct-reading tubes: a hand pump is used to draw air through a glass tube packed with a specific compound. The length of the stain indicates the concentration of the contaminant it was designed to measure. These are less commonly used in office environments and are more suited to measuring the higher contaminant levels expected in industrial settings.

Sampling tubes/canisters: can be passive or used with a sampling pump to collect a defined volume of air pulled through an adsorbent/reactive material and chemically analyzed. Results are used to calculate concentration over a defined period of time, ranging from minutes to days and in some cases months, depending on the parameter and sampling method.

Piezoelectric resonance monitors: air passes through a size-selective inlet, and particles are electrostatically measured with a sensor. The changes in oscillation frequency relate to the particle mass and produce a measurement value.

Optical devices: sensors measure the air as it passes by a size-selective inlet to an optical cell, where the presence of the particles results in light scattering. This measurement is related to the concentration of particles.

Gravimetric methods: use filters and sampling pumps that draw a measured volume of air through the filter. The weight of the particles captured on the filters can be measured as a level of concentration of the particulate. The filter is sent to a laboratory for analysis. These are most often used in research studies and industrial/construction environments.

Direct-reading tubes: a hand pump is used to draw air through a glass tube packed with a specific compound. The length of the stain indicates the concentration of the target contaminant it was designed to measure.

Passive badges: use charcoal or another medium as an adsorbent. Sampling period may be 8 hours to 1 week. The badge is sent to a laboratory for analysis.

Active sorption/chemical analysis: uses tubes packed with a sorbent that traps the VOCs when air is pumped through the tubes. Laboratory analysis is required.

Evacuated canisters: flow controllers allow air to slowly enter a stainless-steel canister. The VOCs are subsequently separated by gas chromatography and measured by mass-selective detector or multi-detector techniques.

Direct reading instruments: instruments such as photoionization, flame ionization and infrared detectors provide total VOC concentrations or speciated data depending on the instrument. Portable gas chromatography - mass spectroscopy (GC - MS) provides speciated VOC data. Instrumentation may be deployed on-site, either directly at the sampling location or indirectly through the collection of grab samples (such as Tedlar bags) collected on-site and analysed off-site.

While measurement methods exist, Health Canada and the NIOSH do not recommend testing for the detection of airborne moulds. See Moulds for more information.

Mould sampling results are also not relevant in the decision to remediate any moisture and mould present in the workplace, as this is necessary regardless of the species or type of mould present. A thorough building inspection is the necessary step, combined with early intervention and remediation.

Sampling may be required in situations where mould is suspected but the source has not been found through a thorough inspection.

The goal of the mould sampling would be to identify if there is mould amplification in the building, which would be indicative of a source of mould that requires remediation. The guiding principles in determining if there is mould amplification in a building are outlined in the American Industrial Hygiene Association publication Recognition, Evaluation, and Control of Indoor Mold, 2nd edition, informally referred to as "The Green Book" (AIHA 2020). Correct interpretation requires a combination of proper training and extensive experience.

If sampling for microbes is to be carried out, a concurrent outdoor sample is always required, except in winter when the ground is snow-covered. A sample can also be taken in an area believed to be free of mould contamination, for example, away from the suspected contaminated area, and then another sample taken in the area of concern.

Viable microbial organism air sampling: Air is sampled to determine the number of colony forming units per cubic meter (CFU/m3). Spores are collected on a growth media appropriate for the types of moulds or bacteria of interest, sent to a qualified laboratory and cultured under the appropriate conditions. This method has the disadvantage that laboratory turnaround times are significantly longer than for non-viable organisms (spore trap sampling), given the 7-14 days required for culturing the samples, as compared to spore trap sampling, which can be analyzed by a qualified laboratory by microscope within hours after sample collection (AIHA 2019).

Non-viable air-borne microbial sampling: Air is drawn through a cassette and impacted onto a sticky surface, which can be analyzed under a microscope for mould, fibres and other biological matter, with mould identified at the genus level (AIHA 2019).

Tape lift sampling: Spores are collected and examined by light microscopy for mould, fibres and other biological matter. This method can show mould density on a surface; however, this method would only be of value if there were uncertainty regarding whether observed contamination is mould, versus dirt. A trained investigator typically can determine this without the need for tape or bulk material samples.

All sampling results should be kept as part of the workplace's documents and recordkeeping. Data includes laboratory results, calibration records, consultant reports and employee records.

When the results received from the laboratory are interpreted, the contaminant's concentration may be compared to health-based exposure limits, if appropriate. It should be noted that many available health-based exposure limits for indoor air contaminants are derived based on chronic (or lifetime) exposure and thus cannot be used in comparison with a single sample or multiple samples collected over a short period of time. In addition, health-based exposure limits are not a definite threshold to determine the safety of an indoor environment. Rather, comparing the concentration levels to the exposure limits would be useful to help determine the existence of a significant source of a contaminant and the potential need for mitigation strategies to reduce exposure. All contaminant concentrations should be kept as low as possible.

As discussed in Volatile organic compounds, each individual VOC has its own inherent toxicity. Therefore, a total VOC measurement (often referred to as TVOC), which does not indicate the individual VOCs included in the measurement or their concentrations, cannot be used to directly assess the health risk of exposure to the VOCs present in the indoor air at the time of sampling.

Determining the meaning of results from monitoring to indicate an acceptable exposure level will be based on accepted occupational hygiene practices and professional judgment. Where guidelines do not exist, other recognized standards and professional judgment will be used to determine at what point hazard controls are required. Recommendations for controls may still be made to address worker comfort and to meet due diligence requirements.

All sampling results must be communicated to the employer, resolution team, health and safety committee representative, supervisor and occupants.

Appropriate persons must be designated for follow-up and corrective actions.

Control measures must be developed and implemented based on monitoring results and data generated by field observations, inspections. All recommendations should consider the control measures guidance described in Taking action and Specific contaminants.

Communication with the building occupants is important when the control measures are being implemented. Occupants can notify the employer if they notice that the controls are not functioning properly or if a new issue arises.

Evaluating control measures may include periodic, scheduled and ongoing monitoring. To evaluate the effectiveness of a control, additional exposure assessments may be required. This step may include re-sampling or a follow-up walkthrough and assessment. Feedback from the building occupants may also be required to determine if the controls are effective or need to be modified.

It is the responsibility of the building operator or employer to ensure hazard controls are implemented and are effective.

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Note: long-term exposure limits short-term exposure limits Purchasing CO alarms: Testing CO alarms regularly Considering an alarm with a low-level display: