Checking Your Ventilation System

By Michael McCann, Ph.D., C.I.H.                          (image: Nederman)

In the last issue of Art Hazards News, I wrote an article, "Industrial Ventilation for a New Art Building", which discussed types of ventilation, choosing a ventilation engineer, planning your ventilation system, and important design factors.  Much of this article is also applicable to individual artists planning ventilation systems for their studios.

Once a ventilation system is installed, or if you have an already existing one, the crucial question is does it work?  If the ventilation system was designed and installed by a ventilation engineer, air flow measurements should be taken to ensure that design specifications are met.  In addition, smoke tube observations should be made to ensure that toxic contaminants are being captured adequately.  This should also be done periodically to ensure that the ventilation system is still working properly.
However, it does not take a trained engineer to do some simple tests to see if your ventilation system is working.  There are some common sense rules and techniques you can use to test the effectiveness of your ventilation system.
Local Exhaust Systems
A local exhaust system, such as a spray booth or slot hood, should capture the toxic contaminants before they get into the air you breathe.
If you can see dusts or mists in the air or on surfaces, this indicates that a local exhaust hood is not working properly.  If you can smell gases or vapors, that is another indication, although you should not rely on your sense of smell since many chemicals do not have detectible odors at hazardous levels.

You can use commercially-available smoke tubes to generate smoke so you can actually see the air flow into an exhaust hood.  A less expensive, but still valid way to check air flow is to use a child's soap bubble kit.  If the soap bubble slowly drifts to the floor, this indicates poor air flow.  The soap bubbles (or smoke) should be steadily drawn into the hood.  You should always make sure that the soap bubbles or smoke are not drawn past your face when in working position, since this could indicate you are being exposed to the toxic contaminants being exhausted.
If the soap bubble test indicates that the local exhaust ventilation system is not working properly, then you must take other steps to find the problem.  The following are some common types of problems with local exhaust systems.

    •    Is there adequate makeup air?  One of the most common problems with exhaust systems is insufficient makeup air to replace the air being exhausted.  The resulting decrease in air pressure affects the performance of the exhaust system.

    •    Is the makeup air source properly positioned?   If the makeup air source is located too close to a local exhaust hood, it can create turbulence and interfere with proper functioning of the local exhaust system, and might even blow the contaminants into your face.  Soap bubbles will show if there is turbulence.

    •    Are there cross-currents?  Local exhaust hoods are often very sensitive to cross-currents caused by heavy traffic around the hood or near air conditioners and other exhaust systems.  Use soap bubbles to check if this is occurring.

    •    Is the process enclosed adequately?  An enclosed process allows the hood to function more effectively.

    •    Are there obstructions or holes in the ducts?  With dust collectors and woodworking machines, the duct is often improperly connected to the machine, allowing air to enter the duct at the connection.  This can interfere with proper functioning of an exhaust system.

    •    Do the ducts have a lot of bends and sharp elbows?  The more elbows in a duct, the greater the loss of efficiency.  This is similar to the effect on water flow of crimping a garden hose.

    •    Have the filters in spray booths been checked?  Clogged or ripped filters will interfere with the operation of the spray booth. Installation of a manometer (available from a spraybooth manufacturer) across the filter can tell you when to change the filters.

    •    Are the fans connected properly?  I have seen instances where fans were connected in reverse, or even where the fan motor was not connected to the power switch.  Connecting a centrifugal fan incorrectly will cause a decrease in air capacity.

    •    Has the fan been checked?  Worn or slipping fan belts, burnt-out fan motors, and damaged electrical connections are all reasons why ventilation systems stop working.

    •    Have there been additions to the ventilation system?  A common problem with older ventilation systems is that additional hoods and ductwork have been connected to an existing ventilation system without determining whether a stronger fan is needed.

    •    Is the exhaust air being recirculated?  Recirculation of exhaust air means that the toxic contaminants are also being recirculated.

Dilution Ventilation
Dilution ventilation systems bring in clean makeup air to mix with and dilute the contaminants to a safe concentration, and the contaminants are exhausted to the outside with a fan.  The following are some problems that occur with dilution ventilation systems.

    •    Is there adequate makeup air?  As with local exhaust systems, there must be adequate makeup air to replace the air being exhausted.

    •    Is the makeup air source positioned properly?  If the makeup air source is located too close to the exhaust outlet of a dilution ventilation system, the makeup air can short circuit directly to the exhaust duct and not mix properly with the contaminated air in the room.

    •    Are the contaminants being drawn past your face?  It is important to make sure that clean air enters the room, passes your face, mixes with the contaminants, and is then exhausted. Soap bubble observations can tell you direction of air flow.

    •    Are obstructions interfering with air flow?  A common problem with ventilation for oil painting is that the vertical easels can block the free flow of air.  Carefully position the makeup air source and exhaust fans to prevent interference.

    •    Is the fan connected properly?  Connecting propeller fans in the wrong direct will cause air to blow into the room instead of being exhausted.  This is easily detected.

    •    Is the exhaust air being recirculated?  Recirculation of exhaust air means that the toxic contaminants are also being recirculated.

Using these simple rules, you should be able to see if your ventilation systems are working properly.  For further information on ventilation, see the CSA's book Ventilation.

Art Hazard News, Volume 16,  No. 4, 1993

This article was originally printed for Art Hazard News, © copyright Center for Safety in the Arts 1993. It appears on nontoxicprint courtesy of the Health in the Arts Program, University of Illinois at Chicago, who have curated a collection of these articles from their archive which are still relevant to artists today.