Air quality

Air quality involves many components, including ventilation, temperature, relative humidity and air contaminants. Ventilation systems used to control air quality can be achieved through the introduction of large quantities of air (dilution ventilation) or at the source where the contaminants are generated (local exhaust). Ventilation requirements during construction, renovation and building maintenance are also critical in ensuring the health of employees and occupants and may require specialized equipment to mitigate air quality problems.

The American Conference of Governmental Industrial Hygienists (ACGIH) publishes a list of substances each year for which they have set new or revised threshold limit values (TLV). You can contact ACGIH to obtain the publication at the ACGIH website.

You will need to create a profile, and then request a PDF copy of the 2016 TLVs & BEIs. Once a profile is created, you can email There is a fee of $25 USD per copy or per person using them.

Yes, although mechanical ventilation systems are preferred, natural ventilation can be acceptable if the concentration of air contaminants, ambient temperature and relative humidity do not exceed levels stipulated in ANSI/ASHRAE standard 62.1-2010 Ventilation for Acceptable Indoor Air Quality or a standard offering equivalent or better protection. Air Quality (

When mobile equipment powered by internal combustion engines are operated indoors or in an enclosed place of employment

  • The engine must be adequately serviced and maintained to minimize the concentration of air contaminants in the exhaust
  • The place of employment must be assessed to determine the potential for exposure of employees to harmful levels of air contaminants in the exhaust
  • Adequate ventilation is required (Air Quality (CCOHS)
  • Mobile equipment is a potential source of carbon monoxide and can create a risk of employee exposure. For more information, visit the following links: Danger: Carbon Monoxide and Safety Talk - Carbon Monoxide (
  • For mobile equipment manufactured after April 1, 2024, and regularly operated indoors:
    • Industrial lift trucks powered by gasoline, propane or natural gas must be equipped with an emission control system that includes a feedback control for air/fuel ratio, and a three-way catalytic converter, or other equivalent measures, or;
    • Industrial lift trucks powered by diesel fuel must be equipped with a scrubber or other emission control system that reduces particulate emissions by at least 70% when tested according to the procedures of the Mine Safety and Health Administration, US Department of Labor, or a standard offering equivalent or better protection

For more information see: Industrial Lift Trucks (CCOHS) and Indoor Use of Propane-powered Forklifts.

An “occupational exposure limit” means

  • except with respect to lead sulfide, formaldehyde, sulphur dioxide, hydrogen sulphide and nitrogen dioxide and any other contaminant for which the Commission sets an exposure limit, a threshold limit value adopted by the ACGIH and set out in the ACGIH publication entitled 2016 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices,
  • with respect to lead sulfide, an exposure limit set at 0.15mg/m3 -TWA,
  • with respect to formaldehyde, an exposure limit set at 0.5 ppm - TWA and 1.5 ppm - STEL,
  • with respect to sulphur dioxide, an exposure limit set at 2 ppm (5.2mg/m3)– TWA and 5 ppm (13mg/m3) - STEL,
  • with respect to hydrogen sulphide, a ceiling of 10 ppm (13.9mg/m3),
  • with respect to nitrogen dioxide, an exposure limit set at 3 ppm (5.6mg/m3)– TWA and 5 ppm 9.4 mg/m3)– STEL, and
  • with respect to any other air contaminant for which the Commission sets an exposure limit, the exposure limit set by the Commission; (limite d’exposition professionnelle)

TLVs is a registered trademark of the ACGIH (American Conference of Governmental Industrial Hygienists). Since the Committee recommended exceptions to the 2016 and 1997 TLVs, the term “threshold limit value” cannot legally be used for these exceptions. Hence a new definition for “occupational exposure limit” which replaces the need for a definition of “threshold limit value”.

Refer to the 2016 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices to see if exposure level for substance in your workplace changed.

WorkSafeNB has not yet set any additional exposure limits. If a hazardous air contaminant is identified that does not have an occupational exposure limit, then WorkSafeNB may set limits. The new OEL of this air contaminant and pertaining information would then be shared with the public on our website. 

The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) standards cited in General Regulation 91-191 excludes health care facilities. The Canadian Standards Association (CSA) governs the requirements for health care facilities which require more stringent ventilation requirements.

A hazard may not be readily apparent because the substance is not detectable by taste, smell, or other (non-harmful) ways. Examples include CO and oxygen deficiency and H2S for some individuals. This would also include substances which OEL is lower than the smell threshold (isocyanates for instance).

If it is part of the workplace process for the powered mobile equipment to go into an enclosed place of employment, then the law applies, even if the regularity is once a week, once a month, etc. If it is an extraordinary circumstance, such as an emergency or a “one off” occasion, then the law would not be applicable.

The extent of the work area assessment required will depend on the circumstances of each workplace. In most cases actual regular measurement of air contaminants or an indicator of them will be necessary.

Measurement of the air contaminant levels may not be needed in circumstances where contaminant levels measured are minimal and exhaust emission controls have been provided, an effective service maintenance program is in place, and workplace ventilation rates are adequate. If at any time the workplace assessment suggests workers may be exposed to levels above the applicable exposure limit, then equipment operation should be suspended until additional controls are provided.

Preliminary assessment
In most cases, a preliminary assessment to determine the general suitability of equipment should be conducted before the equipment is put into operation. An additional air contaminant assessment may also be required, depending on the results of the preliminary assessment.

The preliminary assessment should consider factors such as

  • Is an alternative type of safer equipment available?
  • Can engine exhaust be practicably vented to the outdoors?
  • Frequency and pattern of operation.
  • Type of fuel. Gasoline powered engines generally emit higher levels of CO than other fuel types, while propane and diesel emit higher levels of NO2. Quality of fuel should also be considered.
  • Engine size. Small engines generally emit proportionately higher levels of CO.
  • Exhaust contaminant levels.
  • Types of emission controls. With emission controls, contaminant levels can be expected to be significantly reduced.
  • Natural ventilation rate. The larger the work area volume the greater the natural ventilation rate.
  • Mechanical ventilation rate. The ACGIH Industrial Ventilation Manual, for example, stipulates a ventilation flow rate of 5000 cubic feet per minute (cfm) per forklift; The same is applicable for small engines not designed for indoor operation.

Air contaminant assessment
Some guidance is provided below on the circumstances in which an additional air contaminant assessment is needed.

The initial air testing should be conducted under the conditions in the workplace that are expected to result in the highest exposure levels. If air contaminant levels under these "worst case" conditions are well within the applicable exposure limits (meets with the low exposure level criteria described below), then additional air testing would not likely be required.

Exposure levels are defined as follows:

  • Low exposure refers to exposure levels of less than one-tenth of the corresponding exposure limit.
  • Moderate exposure refers to exposure levels of from one-tenth to less than one-half of the exposure limit.
  • High exposure refers to exposure levels of one-half or more of the exposure limit.

Gasoline/propane/natural gas
For engines not equipped with emission controls, carbon monoxide (CO) can generally be used as a good indicator of overall exposure levels. However, even if CO levels are low, nitrogen dioxide (NO2) exposure levels will also need to be evaluated, particularly if the engine is equipped with a catalytic converter (which reduces CO and HC).

Depending on the level of exposure, the suggested frequency for air contaminant assessment is as follows:

  • Low exposure - no additional air testing is required provided the service and maintenance program is established and maintained. Re-evaluation should be done if conditions of operation change.
  • Moderate exposure - frequency of air testing will depend on exposure levels, types of controls, and workplace experience. In any case re-evaluation should be done at least every six months.
  • High exposure - continuous monitoring for contaminant(s) of concern should be conducted. In any case, at least weekly monitoring is required.

Special cases:

  1. Ice arenas - Experience has shown significant problems with indoor air quality can arise from the indoor operation of the ice resurfacing machine as well as the ice edger. Such workplaces should be equipped with continuous monitoring equipment for both CO and NO2 and monitoring should be conducted at 1.8 metres (6 feet) or so above ice level. Periodic evaluations for CO and NO2 levels should also be conducted in other areas of the arena complex not serviced by continuous monitors.
  2. Construction sites - Since ventilation options may be limited on construction sites, consideration should always be given to use of mobile equipment which does not result in the accumulation of exhaust contaminants in enclosed work areas. Where this is not practical, ongoing monitoring for CO needs to be conducted.
  3. Small engines - Some small portable equipment such as power washers, concrete saws, floor burnishers, and generators may be powered by internal combustion engines. Before using any such equipment indoors, the employer should ensure the equipment is designed by the manufacturer for indoor use. Deaths have occurred due to indoor use of equipment designed solely for operation outdoors. If no other options are practical, then the ventilation rate should be at least 5,000 cfm per engine, or the engine exhaust must be effectively ventilated directly to the outside. In any case, ongoing monitoring for CO will be required.

Although evaluating worker exposure to air contaminants generated by diesel engines tends to be more challenging than with other common fuel types, due to the number of potential air contaminants, diesel exhaust emissions are usually more visible. For example, they contain over 10 times more particulate matter or smoke than gasoline engine emissions. In addition, they are more directly irritating. As such, a more subjective evaluation can also prove useful as a workplace exposure assessment tool.

As a minimum, exposure evaluation will need to include CO and NO2. However, since diesel exhaust generally contains relatively low levels of carbon monoxide, CO alone cannot be used as a reliable indicator of exposure. Nitrogen dioxide (NO2) is a principal concern, but contaminants such as aldehydes and diesel particulate matter may also be significant.

For certain applications, such as where heavy duty or larger diesel engines are being operated, carbon dioxide (CO2) may also be used as an indicator of contaminant levels. For example, where CO2 levels are less than about 1,000 ppm and subjective criteria (smoke, haze, irritations) have also been acceptable, then all contaminant levels associated with diesel exhaust are likely within acceptable limits.

The following table summarizes how CO2 levels and/or a combination of CO and NO2 readings could be used to assess the potential for worker exposure to harmful levels of diesel exhaust components. (The table is adapted from Control of Diesel Exhaust Emissions in the Workplace, Health & Safety Executive, U.K.)

Table: Exposure levels and emission controls




No visible haze in the workplace

Occasional white, blue, or black smoke visible in the workplace

Permanent white, blue, or black smoke

No visible soot deposits

Soot deposits visible

Heavy soot deposits especially near emission points

No complaints or reports of irritancy or other ill effects

A few complaints of irritancy or other ill effects

Worker complaints widespread

CO2 levels less than 800 ppm and/or CO <8 ppm and NO2 levels less than 50% of the exposure limit of 3ppm

CO2 levels near 800 ppm and/or CO levels approaching 10 ppm or NO2 levels approaching the exposure limit

CO2 levels in excess of 1000 ppm and/or CO levels in excess of 10 ppm or NO2 levels above the exposure limit

Controls likely to be adequate - periodic re-evaluation

Controls may not be adequate. Additional assessment for other contaminants will likely be required or additional controls

Controls not likely adequate. Immediately cease operations and decide on new control strategy before resuming. Re-evaluation required

First determine if the dust is combustible. Refer to information provided by WorkSafeBC.

For dust collectors with a volume of 0.6 m3: the dust collector must be located or constructed to ensure that in the event of an explosion, employees are not in danger. For information on combustible dust, please visit WorkSafeBC.

For information on Combustible Wood Dust please see the safety topic at WorkSafeNB | Combustible wood dust  and also information at Wood Dust - Health Effects : OSH Answers (

If you have a wood dust collector with a volume of 0.6 m3 that could endanger employees, then you are required to retrofit the dust collector on or before April 1, 2024.

Good Engineering Practices (GEPs) consist of proven and accepted engineering methods, procedures and practices that provide appropriate, cost-effective, and well documented solutions to meet user requirements and compliance with applicable regulations. (ISPE Good Practice Guide: Good Engineering Practice book published in December 2008)

Note: A useful guide is Industrial Ventilation -- A Manual of Recommended Practice published by the ACGIH.

Measuring carbon dioxide (CO2) levels can be a useful tool to judge effectiveness of ventilation systems, both natural and mechanical. When CO2 is used as a surrogate indicator, analysis of indoor CO2 concentrations can lead to a better understanding of the performance of a ventilation system and the fresh air intake into the space.

CO2 is an easy to measure agent and instantaneous measurements can be taken throughout the day. Humans exhale CO2 with every breath. Thus, as occupants enter an indoor space, CO2 levels inside that space will increase, and so will other occupant-derived pollutant concentrations (bioeffluents) and odours. As ventilation systems introduce fresh air into the space, exhaled CO2, as well as other air contaminants, will be displaced. Therefore, we can judge if the amount of fresh air introduced into a space is sufficient by measuring the resulting CO2 levels.

The ASHRAE standard 62.1 currently cited in General Regulation 191-91 recommends maintaining indoor CO2 levels at no greater than 700 ppm above outdoor air levels which are typically at or below 500 ppm. Therefore, ventilation that maintains peak CO2 concentrations below 1,200 ppm throughout the day would be considered efficient.*

Please note: Carbon dioxide concentration in indoor air is only one of several factors to consider when assessing indoor air quality or when judging acceptability of ventilation systems. Gen. Reg. 191-91 requires non-healthcare facilities to be adequately ventilated by mechanical ventilation conforming to ANSI/ASHRAE standard 62.1-2010 “Ventilation for Acceptable Indoor Air Quality” and allows the use of natural ventilation only if mechanical ventilation is not practical and if the concentration of air contaminants, ambient temperature and relative humidity do not exceed levels as stipulated in the same ASHRAE standard. Please refer to ASHRAE standard 62.1-2010 for further information.

 *This advice might be varied for certain work environments, such as educational facilities, and is not applicable to others, such as beauty and nail salons, disco/dance floors, health care facilities, or health clubs. Work environments requiring a fresh outdoor air rate higher than 15 cfm/person per ASHRAE standard 62.1-2010 can not rely on indoor CO2 level measurements to judge adequacy of ventilation. Please refer to the standard for further information or contact

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