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Inspecting Your Building:
Something in the Air?

UE News, March 1997 (Part I of II)

Your building’s heating, ventilation and air-conditioning (HVAC) systems are designed to provide warm air in the winter, cool air in the summer and general comfort all year round. If operating properly, they can also provide sufficient ventilation to prevent the slow build-up of relatively low levels of toxic gases and vapors in the indoor air.

(But for concentrated sources of pollution, such as welding, or for large volumes of toxic gases and vapors, as in degreasing and other large industrial operations, a good local exhaust ventilation system is needed. We’ll discuss this in the next column.)


If your HVAC is not operating properly, you can have lots of different kinds of problems — you can become drowsy, especially after lunch, due to the build-up of gases such as carbon dioxide. You can develop headaches and become nauseous from the build-up of solvent vapors and/or carbon monoxide in the room air. You can develop allergic skin problems from various chemicals in the room air, and these can come either from use in the building or from outdoor air which get drawn into the building.

In general, if the HVAC systems are not operating well, your office can become a pretty unpleasant place to work in — and I haven’t even begun to talk about your boss yet!

Basically, your HVAC system draws outside air into the building through ductwork (essentially, a system of large pipes) which connects to air supply fans. The air is filtered to remove particles, heated, cooled and/or humidified if necessary, and sent into your work area through the supplied air vents in your office. Then, the air is drawn back through the return air vents by the building’s exhaust fans. Some of this air is exhausted back out of doors, but much of it is filtered and returned to the heating or cooling unit for recirculation with the incoming fresh air.


This recirculation saves the building owners much money, since the circulating air is already heated or cooled as is appropriate. But this recirculation contributes greatly to the unpleasant indoor environment often described as "Tight Building Syndrome" (TBS). Indeed, TBS was a rare phenomenon before 1973; then the oil embargo drove up the cost of gasoline and heating oil and caused some building owners to recirculate up to 90 percent of the indoor air. The resulting TBS crisis made owners back off, but they often still try to recirculate as much of the indoor air as they feel they can get away with.


No HVAC system, not matter how well designed in the first place, can continue to operate properly without an active preventive maintenance program. Here are some basic elements of a good preventive maintenance program. (Thanks go to a fine pamphlet on the subject by the New York State Civil Service Employees Association, Local 1000, AFSCME).

  • Check for obstructions in the outdoor air intake openings. First, are they open during the building’s operating hours? Do they have large wiremesh screens to keep out birds and other "small living creatures?" And are the screens blocked or obstructed? Are they regularly cleaned?

  • Are the air filters for the intake air checked regularly? Are they generally clean when you inspect them? Are the filters the right size to fill the duct, or are they too small — so that unfiltered air can get around them and into the building? How do the filters smell? If they smell bad, this smell can circulate throughout every workroom in the building.


  • Is water accumulating in drip pans? Standing water in pans, ductwork or near intake vents can provide a good home for homeless bacteria and fungi, and easy entry into the building’s circulating air. These can cause Legionnaire’s disease, among others, as well as allergic reactions. Like the drip pans underneath your home refrigerators, these pans need to be inspected and cleaned regularly.

  • Inspect the ductwork. This is usually done by use of access doors or by removing elbow joints and checking the ductwork near them. Are the insides of the ducts clean? Dry? Are there any visible holes in the ductwork, or tears in flexible ducts? Are fire dampers open? Are all access doors closed between inspections?

  • Are heating and cooling coils clean and free of dust or lint?

  • Do the humidification controls and equipment keep the relative humidity between 20 and 60 percent all year round? Do you notice any standing pools of water near this equipment? This is an especially important and potential source of dangerous bacteria in a building.

Workplace Exhaust Ventilation

UE News, April 1997 - Part II of II

Your building’s heating, ventilation and air-conditioning (HVAC) system is supposed to provide a comfortable indoor climate and protect you from small amounts of toxic materials. (In the last column, we discussed the HVAC system and how to check if it’s working properly.)

But when relatively large amounts of toxic vapors and dusts are released in a shop, or when the toxic materials are highly concentrated in a small working area, a local exhaust ventilation system is needed to protect your health and life.

Local exhaust ventilation systems basically consist of ventilation hoods, air ducts, exhaust fans and the motors which power them. It is very important that the hoods be placed as close to the source of the toxic emissions as possible, consistent with letting people do their jobs. This is because the velocity of air being drawn into the ventilation hood falls off very rapidly with distance from the face of the hood.

(For example, if the velocity of air at the center of a simple round pipe six inches in diameter is 85 ft./second at the face of the pipe, it is less than 3 ft./second just 9 inches out along the centerline of the pipe.)


How can you quickly check out how well a local exhaust system is functioning? One way is to get hold of a velometer, a meter which measures air velocity, and put it near the hood and see if the wind velocity is steady and toward the hood. Another quick and dirty check, which is remarkably effective, is to light a cigarette (but don’t smoke it!) and see if its smoke gets drawn into the nearby hood. If the smoke misses the hood or wanders out into the room, you know the local exhaust ventilation system is not doing its job.

Don’t be surprised if you find this with your own system the first time you check it. Like HVACs, if these systems are not regularly checked and cleaned, they quickly become ineffective.

What are some of the common problems which can interfere with a local exhaust system — and what can you do about them?

  • Cross-drafts caused by open doors and windows, operating machines and even lots of people walking by can interfere with airflow in a room, and direct air away from the ventilation hood. Sometimes a ventilation system which worked well in winter will suddenly go haywire in spring and summer when people open windows and/or install air-moving fans. Check out your own shop and see if cross-drafts are interfering with the exhaust ventilation system.

  • Check that enough make-up air is supplied to the building to replace the air drawn out by the local exhaust system. If not, the workplace will become starved for air, and negative air pressure will result. Then air will seep into the room through door cracks and other openings, creating cross-drafts and poor ventilation. You might notice this by the way the door seems to stick when you open it up to get into the room.

  • Check whether too many new exhaust openings have been added to the system over time, beyond what the system was designed to handle. If this happens, all the exhaust hoods will operate at lower air intake velocities, and none will be effective. Often this happens slowly; one vent is added here, later, another is added somewhere else far away. No one added vent seems like it will cause any problem, but together they can be a problem.

  • Check to make sure that the air ducts don’t have holes in them caused by corrosive or acid gases flowing through the pipes. Make sure that abrasive and gritty dusts don’t wear away the ducts at elbow joints. And of course, check that cleaning ports and caps are not left open while the system is operating.

  • Check that air filters are replaced regularly. If they get clogged, the airflow in the system is slowed down.

A few more basic reminders:

  1. Make sure that the vent system doesn’t draw dust and gases into people’s breathing zones. For example, an overhead canopy may do a fine job of drawing vapors or welding fumes up above the source and out of the plant. But if a worker has to put his or her head over the job regularly, the system is then drawing toxins into his or her breathing zone. In this case, a slotted side hood across the worker might give better protection.

  2. Make sure that exhaust vents to the outdoors from the local exhaust system are not located near the intake vents of the HVAC system. This common occurrence causes the toxic emissions to be recirculated into the plant, slowly poisoning all of the workers instead of rapidly poisoning a few. This kind of a vent system (and toxic democracy) none of us need. And you won’t believe how often this happens in real life.

To avoid it, have the health and safety committee walk around the plant and on the roof, and locate every air exhaust vent and every air intake vent. If they are within a few feet of each other at any of these locations, you are having trouble or will have trouble on some days when the wind is blowing in the right (that is, the wrong) direction.

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