Module 07 Ventilation

Slide 1            

Today we will be discussing the types of ventilation systems you may observe in a working entertainment complex. Scene shops, paint shops, welding shops and soldering areas all need industrial ventilation. OSHA experts are called to observe when something is deemed unsafe in the work environment. They are experts in understanding and promoting the safe work procedures and work spaces. The study and installation of ventilation systems is a complex process. This lecture is meant to be an overview of ventilation systems.

 

There are four purposes of ventilation:

1. Provide a continuous supply of fresh outside air.
2. Maintain temperature and humidity at comfortable levels.
3. Reduce potential fire or explosion hazards.
4. Remove or dilute airborne contaminants

Ventilation is considered an “engineering control” to remove or control contaminants released in indoor work environments. It is one of the preferred ways to control worker exposure to air contaminants.

Other ways to control contaminants include:

eliminate the use of the hazardous chemical or material, or substitute with less toxic chemicals.[1]

Slide 2 Types

• Comfort
• HVAC (primarily for comfort)
• Air conditioning
• Industrial
• dilution and removal by general exhaust
• local exhaust (see Figure III:3-1)
• makeup air (or replacement)
• re-circulation systems.

Slide 3 Comfort HVAC

HVAC is used to provide sufficient air movement for health and safety in nonindustrial work environments.

Recirculating system uses fans or blowers to circulate air through ducts, moving inside air out and blowing clean air from outside in.

Slide 4

Recirculates interior air. Not for industrial use.

Slide 5

OSHA Specifies the minimum ventilation rates and indoor air quality that will be acceptable to humane occupants and is intended to minimize the potential for adverse health effects.

If you are sitting in a lecture hall of the library 15-20 cubic feet per minute per person of outside fresh air is delivered to the level at which you are breathing.

1. Recommended Ventilation Rates

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) established recommended ventilation rates for indoor environments in 1973.²

(ASHRAE amended this standard in 1975 to specify the minimum value of 5 cubic feet per minute (CFM) of outdoor air per person be used in building design. This standard has been incorporated into the building codes of many cities and states.³)

The 62-1989 standard recommends a minimum of 15 CFM of outdoor air per person for offices (reception areas) and 20 CFM per person for general office space with a moderate amount of smoking. Sixty cubic feet per minute per person is recommended for smoking lounges with local mechanical exhaust ventilation and no air recirculation.⁴

1. Acute Health Effects of Major Indoor Air Contaminants
2. Types of Building Problems

Employee complaints can be due to two types of building problems: sick or tight building syndrome and building related illnesses.

Sick building syndrome is a condition associated with complaints of discomfort including headache; nausea; dizziness; dermatitis; eye, nose, throat, and respiratory irritation; coughing; difficulty concentrating; sensitivity to odors; muscle pain; and fatigue. The specific causes of the symptoms are often not known but sometimes are attributed to the effects of a combination of substances or individual susceptibility to low concentrations of contaminants. The symptoms are associated with periods of occupancy and often disappear after the worker leaves the worksite.

Building-related illnesses are those for which there is a clinically defined illness of known cause of disease and include infections such as legionellosis and allergic reactions such as hypersensitivity diseases and are often documented by physical signs and laboratory findings. A more thorough description of these illnesses can be found in the American Conference of Governmental Industrial Hygienists (ACGIH) guidelines on evaluating bioaerosols.

⁵Major Indoor Air Contaminants

OSHA Technical Manual of indoor air quality investigation link is below if you want to learn in more detail.

https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_2.html

Slide 6

• Dilution
• Local exhaust

Slide 7

Dilution mixes contaminated air with large volumes of clean air to reduce the amount of contaminants to acceptable levels. These systems include Inlets for Fresh air in; with fans Outlets exhaust fans to push bad air out.

Dilution Has limited uses-not for use with controlling dust, mists or highly toxic air contaminants.

Dilution ventilation controls pollutants generated at a worksite by ventilating the entire workplace. The use of general ventilation distributes pollutants, to some degree, throughout the entire worksite and could therefore affect persons who are far from the source of contamination.

Dilution ventilation can be made more effective if the exhaust fan is located close to exposed workers and the makeup air is located behind the worker so that contaminated air is drawn away from the worker’s breathing zone. http://www.ccohs.ca/oshanswers/prevention/ventilation/introduction.html

What are the limitations of dilution ventilation?

As a method for protecting workers, it is important to know that dilution ventilation: Does not completely remove contaminants. Cannot be used for highly toxic chemicals. Is not effective for dusts or metal fumes or large amounts of gases or vapors. Requires large amounts of makeup air to be heated or cooled.

Slide 8 What dilution is commonly used for:

Dust                     sandblasting

Mist Aerosol      spraying

Heat hot wire     cutting of plastics

Vapor acid          etching of Gobos

Slide 9

What is local exhaust ventilation? Local exhaust system is used to control air contaminants by trapping them at or near the source, in contrast to dilution ventilation which lets the contaminant spread throughout the workplace. Local exhaust is generally a far more effective way of controlling highly toxic contaminants before they reach the workers’ breathing zones. This type of system is usually the preferred control method if:

Air contaminants pose serious health risk. Large amounts of dusts or fumes are generated. Increased heating costs from ventilation in cold weather are a concern. Airborne contaminant sources are few in number. Emission sources are near the workers’ breathing zones. In a general way, a local exhaust system operates similar to a household vacuum cleaner with the hose as close as possible to the place where dirt would be created.

Slide 10

What are the components of local exhaust ventilation?

A local exhaust system has six basic elements:

A “hood” or opening that captures the contaminant at the source.

Ducts that transport the airborne chemicals through the system.

An air cleaning device that removes the contaminant from the moving air in the system (not always required). Fans that move the air through the system and discharges the exhaust air outdoors. An exhaust stack through which the contaminated air is discharged. Make up air that replaces the exhausted air.

Slide 11

What should I know about make-up air?

An important and sometimes overlooked aspect of local ventilation is the need to provide enough air to replace the air that is exhausted from the workplace. If enough make-up air is not provided when large volumes of air are exhausted, the workplace becomes “starved” for air and negative pressure is created.

Negative pressure in the workplace increases resistance on the ventilation system causing it to move less air. Air will also enter a building through cracks around doors or windows or other small openings to try to “equal” the rate of air being removed. The result is that workers may be exposed to cold air in the winter, and additional heating costs may occur. One simple way to judge if a building is under an excessive negative pressure is if you have difficulty opening a door that pushed into the room or building (the air wants to force the door closed).

A separate intake fan, located away from the exhaust fans, should be used to bring in fresh, uncontaminated air from outside. This air must be clean and heated in winter or cooled in summer, as needed.

Slide 12

Round ducts

In industrial systems all the ducts are round. The idea behind this is to not allow contaminants any square or sharp edges to adhere or catch on and clog up the system. By having round ducts all the air contaminants move through the system and out the filtered end

Slide 13

• Duct collection system
• Booth
• Slot hood system

The small ventilation systems for dust collection include booths and slotted hoods.

Slide 14 Dust collection systems for multiple tools

Some scene shops use dust collection systems. They install pick up hoods at each tool. The hood is by each tool so that as materials are cut the dust is immediately vacuumed up leaving the air in the work environment clean.

Slide 15

This is a table saw with a small ventilation system hood. As the wood is cut the dust is vacuumed up away from the work environment atmosphere.

Slide 16

Both these areas have small dust collection systems. The Bosch table saw comes with its own vacuum bag. The system o the right uses a portable vacuum to suck up the dust.

Slide 17 Ventilation Booth

In the auto motive industry booths are built large enough to park a car inside. When work is being done on the vehicle, the air is ventilated. Allowing the worker a clean space in which to work.

 

Slide 18 Slot hood fume system

These are used in chemical applications where workers are using small products and need the contaminants to be vented away from them immediately

 

Slide 19

What do you think of this picture? What are the problems? What is happening to the worker?

And where is the air being pulled?

Slide 20

This system is a little bit better. But I bet we could do more.

Slide 21

This system is pushing clean air onto the worker as well as pulling the contaminated air away. And it has a make up fan to be sure the air is balanced.

Slide 22

This system is the best. It takes into account all the needs of the worker. Pulls the bad air away from the worker while pushing good air towards him.

 

Slide 23

Recommendations for the Employer by OSHA

1. Engineering Recommendations

Ventilation

Includes the use of natural, dilution, local exhaust, or increased ventilation efficiency. The most effective engineering control for prevention of indoor air quality problems is assuring an adequate supply of fresh outdoor air through natural or mechanical ventilation.

SHRAE in its 62-1989 standard recommends 20 cubic feet per minute (CFM) of outdoor air per occupant for offices. Room air in which contaminants are generated should be discharged directly outdoors rather than recirculated.

 

Efficiency

Ventilation efficiency can be improved by: Ensuring that outdoor air-supply dampers and room air-vents are open; Removing or modifying partitions or obstructions that block fresh-air flow; Rebalancing the system to prevent inflow or outflow of contaminated air due to pressure differentials between rooms; Preventing poor distribution of make-up air by proper placement of air inlets and exhausts; and Using room fans to improve mixing and dilution of pollutants. Outside air intakes should not be located in close proximity to potential sources of contamination (automobile garages, cooling towers, building exhausts, roadways). https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_2.html

Slide 24

Always have an expert design your ventilation system to be sure you have followed all codes and procedures.

Bibliography

http://www.ccohs.ca/oshanswers/prevention/ventilation/introduction.html

http://www.business.govt.nz/worksafe/information-guidance/all-guidance-items/welding-and-local-exhaust-ventilation

http://www.ehsdb.com/industrials-ventilation.php

http://bangaloreairtech.com/iahcs.html

http://www.aessolutions.co.uk/services/lev-system-design/

https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_2.html

[1] Dust collection systems for multiple tools