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Ventilation

Definition

Ventilation is the process of supplying fresh air air to an enclosed space in order to refresh/remove/replace the existing atmosphere. Ventilation is commonly used to remove contaminants such as fumes, dusts or vapors and provide a healthy and safe working environment; in other words, it is an engineering control. Ventilation can be accomplished by natural means (e.g., opening a window) or mechanical means (e.g., fans or blowers).

By itself, the term does not indicate whether the exhausted air is filtered or cleaned before being discharged. Likewise, it does not indicate whether the incoming ("make-up") air is treated is heated, cooled or otherwise treated. Ideally, ventilation provides constant temperature, humidity and air quality within the enclosed space.

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Ventilation is a critical concern in many occupational activities that generate dusts, fumes, mists, and vapors. Examples of such activities include welding, grinding, soldering, brazing, sanding, painting, finishing, and the use of volatile and/or flammable chemicals. It has also become an important issue for schools, restaurants and other spaces given the ease with which Covid-19 is transmitted through heating and cooling systems.

One can reduce the need for ventilation by reducing or minimizing the amount of airborne contaminant generated. Examples of such practices include:

Ventilation systems for the control of hazardous materials in the workplace can be broken into two broad classes:

  1. General ventilation (also called dilution or fresh air ventilation) simply dilutes the concentration of the hazardous material in the air by bringing in fresh air. Examples include window and cooling fans - or simply opening a window. General ventilation is feasible only when all of the following apply:
    1. The quantity of hazardous material is small and constant.
    2. The air movement is sufficient to keep the concentration of hazardous material at acceptable levels.
    3. The materials have low toxicity and flammability.
    4. The material will not otherwise adversely affect the surroundings or other workers (corrosion, foul odors, harmful dusts).
  2. Local exhaust ventilation (LEV) is a form of engineering control that encloses the material, equipment or process as much as possible and ensures that air flow is into the enclosure at necessary rates. A good example is a fume hood. For local exhaust ventilation to work properly:
      Do not block or obstruct the air intake or the fresh make-up air source.
    1. Perform operations within the fume hood or air intake area.
    2. Do not position yourself between the contaminant source and the air intake - otherwise you will be exposing yourself to high concentrations of the contaminant.
    3. Make sure the ventilation system is operating properly and is not damaged.
    4. Ensure that the ventilation system is compatible with the materials you are using - for example, special fume hoods must be used for perchloric acid to prevent the buildup of dangerously explosive deposits in the ductwork!

Local exhaust ventilation is clearly the preferred method whenever feasible! In addition, local exhaust ventilation moves a much smaller quanitity of air much more efficiently - this results in large savings in heating and cooling costs.

Local exhaust ventilation systems typically have the following components:

  1. An enclosure or inlet to collect the contaminated air at the source of its generation (or as close as possible).
  2. Ductwork which conveys the contaminated air away from the source.
  3. In some cases, a filter or other device to remove the contaminant from the airstream.
  4. A fan or other air-moving device to provide the necessary air flow.
  5. An exhaust for discharging the cleaned or contaminated air.

Some specific examples of local exhaust ventilation systems include:

Fume Hoods - These specialized, fixed cabinets contain and draw in contaminants and vent the contaminated air remotely (usually through a stack on the roof of the building). A good supply of properly conditioned makeup air is required so these systems require professional installation and maintenance. fume hood picture
Ventilating Blowers - These have an inlet and outlet hose to collect and move contaminated air away from the source. The model shown here (without the hoses) is portable, making it ideal for use in a garage or workshop. Ventilating blowers generally have the lowest capital cost of the systems shown. ventilating blower picture
Fume Extractors - These are small air cleaning devices used to filter mists, dusts and fumes. The filtered air is recycled - making it good for many common dusts. Because the air is recycled, this is not a suitable choice for toxic or flammable vapors.

fume extractor picture
Filtering Stations - Are fundamentally similar to the fume extractors shown above, but have better mobility. filtering station picture
Down Draft Work Stations or Tables - These use a blower to pull air away from the worker through slots or holes in the table top or work surface. Down draft stations can have a filtering/recirculating configuration (like the filtering station above) or the exhaust can be ducted to a remote point (like the ventilating blower above).filtering station picture

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SDS Relevance

Some Safety Data Sheets' will contain specific mention of engineering controls such as local exhaust ventilation. These should be found in Section 8 (exposure controls/personal protection). Remember, the preferred methods for reducing chemical exposure, in order of general effectiveness, are:

  1. Substitution of less hazardous materials or processes.
  2. Engineering controls.
  3. Administrative controls
  4. Personal protective equipment (PPE)

Also remember that flammable materials or combustible dusts can be ignited if your ventilation system is not properly designed and maintained.

Further Reading

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See also: administrative controls, dust, engineering controls, fume, personal protective equipment (PPE), respirator.

Additional definitions from Google and OneLook.



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