Air Quality Controls Flashcards
What is the equation for flowrate?
flowrate = velocity * area or Q = V*A
What are the units for flowrate, velocity, and area?
Flowrate (cfm), velocity (fpm), Area (sq feet, may need to convert from sq inches)
What is the equation for square ducts?
L*L
What is the equation for round ducts?
(pie)(r)squared
What size particles would a hopper (mechanical process) create?
inhalable
What size particles could a furnace or smelting create?
respirable
Do you still need PPE if there are engineering controls in place? Give an example.
Yes
ex) always want to protect hands with gloves
What are some controls at the emissions source?
- substitution
- automation
- process change
- isolation of the source
- enclosure of the source
- local ventilation
- dry to wet methods
- preventative maintenance
What controls can be used at the air path?
- change air direction
- dilution ventilation
- increase distance from emissions source
- erect a barrier
What controls can be used for protection at the receiving employee level?
- move worker out of air path
- education and training
- respirators
- enclose the worker
- rotation
What type of control is ventilation?
engineering
What is the goal of ventilation?
to dilute or remove contaminants
How does ventilation work (very general)
Strategically supplies (adds) or removes (exhausts) air
Explain how dilution ventilation wrks
- local- supply of clean air passes the source, and toxins are sucked into an exhaust and released from an outlet
What is general ventilation used for?
Comfort- to warm up or cool off
Explain how general ventilation works
Outdoor air enters the system, air also enters the system from the return air grill. Both intakes enter the mixing chamber and go through a filter. Next the air goes through a fan and then a heating or cooling coil. It may go through a humidifier, and then diffuses into the room or building. From there, the air enters the return air intake, some is exhausted and some is recycled
What is the purpose of a filter in a general ventilation system?
Protect the fan/ equipment- does not clean out chemicals
What are the components of a ventilation system?
- source of clean air
- possible air cleaner
- fan & motor
- may ave ductwork
- supply grilles or terminal device (return air grill)
- return/ exhaust
What is the air blowing in/ air provided to the space called?
supply side
What type of ventilation is used for comfort or dilution of nontoxic/ low toxic substances?
general ventilation
What type of ventilation is used for exhausting toxic chemicals?
dilution
What are the types of general ventilation systems?
- constant volume (heat/ cool in response to thermostat)
- variable volume ( add volume of heated or cooled air to temper)
- Unit ventilators (used in individual rooms; blower, re circulation, damper for outside air)
What ventilation systems are typically used in commercial buildings?
Constant volume
Does the blower ever stop in constant ventilation systems?
No
Where is variable volume ventilation commonly used?
in homes- air turns off and kicks in when you need
What is a major consideration to make when building a ventilation system
Source of outside air, is it clean?
location can make it vulnerable (ie if it’s too low and a smoking area or parking lot is put nearby)
What regulates the volume of air in a general ventilation system?
damper (acts like blinds)
What is the percentage of IAQ problems that ventilation is responsible for?
50%
How can problems with the ventilation system cause IAQ issues?
- inadequate outside air –> buildup of agents
- inadequate distribution or heating or cooling or drafts –> discomfort
What is a good design for exhaust and makeup air?
Place the inlet at the top of the building, away from the outlet
What is makeup air
the clean air taken in
What are some potential issues with having an air intake vent that is too low?
- chimney effect- hot air rises through building
- smoke from ETS
- emissions fro cars
- weather events like snowstorms
how to fix air intake vents that are too low?
add pipes to vent upwards
What are other potential issues with general ventilation systems?
- materials used could produce problems like fire risk or microbial growth
- return air systems not obvious- ie special ceiling tiles with slots
- backdraft dampers and sprinkler systems may be needed in some situations
What is the goal of local exhaust ventilation systems (LEV)
to remove contaminants at the source, acts similar to a vacuum
What does the contaminated air go through in the LEV that actually cleans it?
Cyclone or filter bag
What does the exhaust in the LEV system do?
Suctions the air so it is removed from the space
What are the components of the LEV on the exhaust side?
1) Hood or exhaust grille or return air register
2) ducts or ductwork
3) air cleaner
4) fan & motor
5) other- return air plenums, passive returns
What is the purpose of the hood?
Air drawn in to capture the contaminant
What is the purpose of the ductwork?
Connects the compnents
What is the purpose of the air cleaner?
removes materials before discharge
What is the purpose of the fan/ motor?
energy to draw air
What are the types of hoods?
1) Capture hood
2) enclosure hood
3) Receiving hood
Describe the capture hood
- reach out to capture and pulls in contaminants
- cannot be more than 2 ft from contaminant
- efficiency affected by cross drafts
- placed along side the contaminant
Describe the enclosure hood
- surrounds the source and contains the contaminants
- ex- lab hood
- not intended for working inside
- turbulence draws the contaminants out
Describe the receiving hood
- catches contaminants
- canopy and some grinders
- needs process to emit sufficient air to carry contaminants
What is needed for a receiving hood to work?
Heat
what type of hood is a lab hood?
enclosure hood
what type of hood is a kitchen hood?
Receiving hood
What happens when a person stands in front of a lab hood?
Creates turbulence and air can recirculate
How do biohazard hoods work?
They have an air curtain
What should canopy hood be limited to?
situations that can take advantage of thermal updrafts
what is crucial in all systems and if not adequate can cause problems?
makeup air
in addition to air quality, want can god ventilation systems help to improve?
housekeeping
What is an enhancement to the canopy hood?
slot hood with push/ pull. system pushes air in and pulls on the other side (similar to air curtain but not up and down)
What problems can occur with push/ pull slot hoods
cannot push more than you pull, needs to be balanced
What needs to be considered when designing a ventilation system?
- work efficiently
- cannot interfere with worker and job
- maximize pressure losses (need air to move as fast as it should)
- needs to be the correct size to properly exhaust the air
How can fans impact ventilation system?
Can create drafts and redirect the air/ contaminants
Flaps on the side of the hood
flanges
what is the purpose of the flange
prevents air from back or sides from entering, only air that enters is directly below/ in front of hood
What design considerations impact ducts?
- material
- diameter
- round/ square
- smooth vs. flexible ducts
What are the different materials that can be used for ducts?
Stainless steel
plastic
galvanized steel
galvanized aluminum
When should plastic be used for ducts?
with corrosive chemicals
What should be considered when determining the diameter of the duct?
- cost- more material/ harder to install
However- operating costs are lower for larger diameters since it handles larger amount of air
What happens to the air at the duct surface/ walls?
air friction, slows down the air velocity, which is worse with corrugated materials
Which is a better design, round or rectangular ducts?
Round- less resistance
Why are rectangular ducts used/
Cheaper due to lower labor cost
What are the benefits of smooth ducts?
less losses compared to flexible ducts
What are the benefits of flexible ducts?
more flexible and easier to install
What is better, a wye joint or a t joint?
wye joint- less impaction
What texture/ shape/ transition of duct would have the least resistance?
smooth, round, gentle transition
What should you avoid in ducts?
- flow disturbances
- narrow elbows
- perpendicular joints
Why do you want to ensure that the velocity is not too high through the ducts?
- increases turbulence which increases losses
- increases overall flowrate which increases cost due to fan size and electricity use
What are air cleaners used for?
to remove aerosols and decrease contaminants discharged into the environment
What are the different types of air cleaners for aerosols?
1) baghouses
2) cyclones
3) Electrostatic precipitators
4) scrubbers
How do baghouses work?
Collect aerosols in a bag
How do cyclones work?
air circulates inside and aerosols hit the sides and drop out
How do electrostatic precipitators work?
charge and attract particle in an electric field
How do scrubbers work?
contact particles with liquid, water makes particles heavy and they fall
What are the parts of the air cleaner?
Removed material collection
- air cleaner
- fan
- motor
What are the different types of air cleaners for gases?
1) Spray chambers
2) Adsorption beds or activated carbon systems
3) thermal oxidation systems
Describe spray chambers
liquid scrubbers contact gas, gas molecules transfer to liquid (absorption), droplets collected
Describe adsorption beds or activated carbon systems
gas adheres to surface of porous material, reversible process (can cook in oven to release the gas)
Describe thermal oxidation systems
burn combustible contaminant
Give an example of a thermal oxidation air cleaner?
waste to heat incinerators
What is the purpose of the fan in the ventilation system?
- generates suction to draw contaminated air
What are the two main classes of fans?
- centrifugal fans
- axial flow fans
How do centrifugal fans work?
- air goes in the side and thrown out at a 90 degree angle
What are the benefits of centrifugal fans?
- quieter, cheaper, and can be used with high pressure
- can handle resistance or losses
Where are centrifugal fans used?
LEV systems
Describe axial fans
- straight line exit and entry which is parallel to fan shaft
Why can’t axial fans be used for local exhaust?
cannot push or pull against losses or resistance, not as good at creating suction
suction only good for about a foot behind, but can blow up to 30 ft
What is an example of an axial fan?
home fan
What are axial fans good for?
Blowing NOT suction
What can be used to close a part of the ventilation system to ensure proper air pressure?
Blast gates
How does the movement of air in an LEV system work?
hoods –> ducts –> main duct –> fan –> air cleaner –> outdoors
Some systems have the fan and air cleaner reversed
What is the part of the laboratory hood that can be pulled into position?
the sash
velocity at the entrance of a hood
face velocity
how is duct velocity measured?
through holes made on the sides and bottom of ducts
How should velocity measurements be taken?
at equidistant points, compute an average
What is the problem with air cleaners?
They cause significant resistance to air movement
What is resistance?
the pressure drop
How can you prevent resistance?
maintenance and cleaning
What are the benefits of centrifugal fans?
- produce more negative static pressure to overcome resistance to air movement and provide wider range for flowrates to produce optimal face velocities at each hood and through each duct
What is the last choice for air quality control?
respirators
When are respirators appropriate?
- temp solution to temp prob
- supplemental to ventilation
- emergency situations
What are the three types of face masks?
1) Quarter
2) half
3) full
What are quarter respirators effective at filtering?
Aerosols, not gases. The entire surface is a filter material (think surgeon mask)
What can half masks filter?
Can add different cartridges to filter different things (gas or OM)
What is the purpose of full face masks?
They provide protection against air pollutant AND protect the eyes
Give examples of when you would want to use a full mask respirator
- when working with splattering chemicals or sparks
Describe the air purifying respirator
the workplace air is cleaned by the respirator and breathed by the wearer
What is the difference between a filter and a cartridge?
filter- traps aerosols
cartridge- captures gasses
name for the respirator that uses your breathing to supply air?
air purifying respirator
Can a respirator block both gases and aerosols?
Yes- with a combined (filter and cartridge) unit
This unit is powered, but still uses your body’s breathing to supply air
PAPR- Powered Air-Purifying Respirator
What are the two types of respirators?
Air purifying respirators (use your body’s breathing to supply air)
Air supplied respirators/ atmosphere supplied respirators- air provided
Described the atmosphere supplied/ air supplied respirator
- air provided, wearer does not breathe the workplace air
- airline or self-contained breathing apparatus (SCBA)
When do you need to use air supplied respirators?
When there is not enough oxygen in the surrounding environment
What are the problems with respirators?
- uncomfortable
- hard to communicate
- air leaks due to differences in face shapes/ beard
- not suitable for everyone (ie those with asthma)
- need maintenance
- worker responsibility to use properly
What are the benefits of respirators?
- good protection that is easy to carry with you
- cheaper than engineering controls
Describe the difference between negative and positive pressures in in respirators
Negative- Air pushing on mask from outside
Positive- air blown into mask from inside
What type of air leak can occur with negative pressre?
Outside air leaks into mask
What type of air leak can occur with positive pressure?
air can leak out
What type of pressure is a concern with atmosphere supplied respirators and PAPRs?
positive pressure (air leaking out)
What is a common qualitative fit test? Is it effective?
- cover the sides of the mask to test for suction (positive pressure)
- cover the exhale portion of the mask to test if it blows out (negative pressure)
- should remain securely on face
- NO- some masks cannot be plugged easily, and may seem like you have a good fit when you do not
What is a second qualitative test?
Saccharin, Bitrex, or irritant smoke
How does quantitative fit testing work?
use equipment to measure concentration outside of mask and inside of mask, calculate the protection factor
What is the equation for protection factor?
concentration outside / concentration inside
When are your required to do a quantitative fit test?
If you need to meet a protective factor of 500 or more (concentration outside / concentration inside)
When can you use a qualitative fit test?
PF <500
How do you determine the assigned and required protection factors?
Review OSHA assigned protection factors
What activities must be completed while testing respirators?
- Normal and deep breathing
- turning head side to side
- grimacing
- bending over
- talking (rainbow passage)
Per OSHA, who is responsible for supplying the respirators?
employer
What are the parts of the respiratory protection program?
- person in charge supported by management
- exposure assessment
- selection of respirator based on hazard
- Use of NIOSH approved respirator
- Written SOPs
- Medical Clearance
- Fit testing
- Choices
- Training
- Program evaluation
- Records
- Cleaning and Maintenance
- Respiratory protection standard
How do you select the respiratory type?
Use the document from NIOSH
