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Ventilation in Your Workplace
Is It Clearing the Air?

No workplace receives 100 percent fresh, outside air. Usually, the fresh air is mixed with used workplace air and then circulated. In some buildings, the outside air dampers are shut and there is virtually no fresh air. The same air may be re-circulated and breathed over and over again. This is what to look for in evaluating your ventilation system:

Does your workplace have a ventilation system? This is not as odd a question as it may seem. Some buildings do not have ventilating systems. You can check to see if yours does by walking around and looking for vents and ducts.

Is the system on all the time? Often, the air circulation in a building will stop at 5 P M. or on weekends even though people may regularly work late or night shifts. In some workplaces, large jobs are done at night, and machines can produce a high volume of pollutants. You can test whether the system is on by holding a tissue near the vent. A ribbon or streamer can also be taped to the exhaust vent grills. If it moves, air is being circulated. Check this before and after 5 P M.

Is the system continuous or does it go on and off during the day? Some ventilation systems are on a time cycle. This means that the blower will turn on and off at regular intervals throughout the day. If your workplace is constantly generating air pollutants, the pollutants will accumulate while the system is off. Check the air vents regularly during the day to find out if you are getting fresh air continuously.

Does each room have a vent? Make a list of the number of vents per room. Make sure you look on the walls and floors‑‑and remember, no vents, no air.

Are the vents for supply and exhaust right next to each other? When supply and exhaust vents are too close, the clean, fresh air gets sucked out of the room before it has adequately circulated. This is a common result of poor engineering design.

Are the vents blocked in any way? Exhaust and supply vents will work only if the air can move freely around them. Blockage by walls, partitions, or even piled-up boxes or files will obstruct air flow and reduce ventilation efficiency.

Are there any "dead spaces" in your workplace? "Dead spaces" are those in which air is not replaced and therefore pollutants are allowed to build up. You can check to see if there are any in your workplace by lighting a match and noticing how the smoke moves. Does the smoke flow toward an exhaust vent or simply stay in one place? If the smoke doesn't move, other pollutants will also remain in the air. The main reason for dead spaces is poor placement of supply and exhaust vents. Dead spaces can also occur if there has been a change in the layout of the workplace, such as putting up partitions.

Do you have control over your vent system? You may be able to enter the fan room and turn up the blower or fan supplying the air. Check with building maintenance to see.

Is there a smoke detector in your ventilation system? It should be located in ducts taking the air out of the workplace.

Is the temperature and humidity adequate? The importance of a comfort­able temperature is obvious. But comfort also means proper humidity, or water vapor in the air. When the workplace air is too dry, your nasal passages dry up and you may get headaches and become more susceptible to colds, flu, and other infections. When the air is too humid, you also feel uncomfortable. Humidity makes a cold room feel colder and a hot room seem hotter.

Is there a program of regular maintenance of the ventilation system and equipment? Such inspections should include:

___checking damper positions.

___checking belts, baffles, duct work, and filters.

___checking ventilation intake/exhaust vents.

___measurement of actual air flow to all areas where people work.

___checking the carbon dioxide levels in the air.

LOCAL EXHAUST SYSTEM

An effective ventilation system cap­tures dust, vapors or fumes right at the point where they are created ‑‑ so they never have a chance to be breathed by a worker.

This local exhaust ventilation is dif­ferent than general room ventilation, which circulates air in the workplace mainly to make workers feel more comfort­able.

Enclosures around the equipment keep dust or fumes from escaping into the air. They also cut down drafts, making it easier for the hood or hose to suck up the dust or fumes. A flange around the hood also helps enclose the area where the dust or fumes are being generated and can increase the efficiency of the hood. Enclosures lined with sound proofing material can cut down both dust and noise levels.

Hoods are placed right at the source of the dust or fumes. They vary in design. For example, a circular guard enclosing a grinding wheel can also be a ventilation hood if it is connected to a duct to remove the dust. Other hoods suck in dust at the curve in a belt sander or into a clip-on hose attached to a power tool.

Air speed must be adequate for capturing the dust and drawing it into the hood. Ventilation experts call this speed the "capture velocity."

Fresh air ("make-up air") should be blown into the room to replace air sucked out into hoods.

CHECKING YOUR SYSTEM

Here are some questions to ask to check whether a local exhaust ventilation system is working correctly:

1. Do you smell chemical odors or see dust building up near the hood or machines? Is there dust in the air?
2. Is the hood close enough to the place where the dust, fumes, or vapors are being created?
3. Does the hood pull dust or fumes in the right direction ‑‑ away from the worker's face rather than past it?
4. Are the ducts plugged? Listen for a "thud" when you tap the duct. Are filters clogged?
5. Are any ducts broken or leaking?
6. Check motors and fans to see if belts are broken or fans are installed backwards.
7. Ask your employer to show you the original design of the system to see if extra hoods have been added to go over new machines. If any were added, was the system balanced again? Can it handle the new load?
8. Are there crossdrafts that blow dust or fumes away from the hood opening? Could the operation be enclosed with shields or booths to prevent drafts?
9. Are there lots of bends, twists or Ys in the duct system? These can slow down the movement of the exhaust air ‑‑ as well as increase noise levels.
10. Does the amount of clean, make-up air brought into the system equal the amount exhausted? If you have trouble opening doors because of "negative pressure," this may be a sign that more fresh air is needed.
11. Is the air flow strong enough?  Ask the employer to use an instrument called a velometer to measure it.
12. Is the system actually keeping hazardous materials out of the air?  Ask your employ­er to show you measurements of the levels of chemicals or other materials in the air. A ventilation system is only useful if it actually protects workers.

Courtesy of TheWorkSite.org.