Chapter 7 - Ventilation

Question 1

Three methods to reduce or eliminate any hazard from the workplace

Answer 1

Engineering control
Administrative control
Personal protective equipment

Question 2

Ventilation

Answer 2

Engineering control to reduce or eliminate the concentration of hazardous materials in the work place

Question 3

Primary purposes for ventilation

Answer 3

1- maintain adequate oxygen supply
2 - control hazardous concentrations of chemicals
3 - remove odors
4 - control temperature and humidity
5 - remove contaminants at the source, before they enter the workforce

Question 4

Three categories of ventilation

Answer 4

general, dilution, and local

Question 5

General dilution

Answer 5

primarily used for comfort, such as temperature, humidity, and odor control, such as air conditioning or heating

Question 6

Dilution Ventilation

Answer 6

system designed to dilute contaminants by mixing with fresh air
Components include, air exhaust, source of air sully, a duct system and a method to filter and temper incoming air
Used to control - contaminants of moderate toxicity, a large number of sources, intermittent exposures, or where emission sources are well distributed

Question 7

Local (exhaust) ventilation systems

Answer 7

Designed to control contaminants at the source before mixing with breathing air occurs
Used to control - highly toxic substances, single source emissions, direct worker exposures

Question 8

Air movement results from

Answer 8

differences in pressure

Question 9

Difference in pressure can be attained by

Answer 9

heating or mechanical means

Question 10

Temperature gradient

Answer 10

contributes to ventilation

Question 11

Volumetric Air flow

Answer 11

Multiply velocity by cross-sectional area in which air flows

Q= V * A

Question 12

Air moves from

Answer 12

area of higher pressure to area of lower pressure

Question 13

Pressure created by fan is referred to as

Answer 13

static pressure

Question 14

Static pressure on the downstream side of a fan is

Answer 14

Positive

Question 15

Static pressure on the upstream side of a fan is

Answer 15

negative

Question 16

Velocity pressure

Answer 16

the pressure in the direction of flow necessary to cause the air at rest to flow at a given velocity

Question 17

Total pressure on a ventilation system

Answer 17

Equals the sum of static and velocity pressure

Question 18

Equation for total pressure

Answer 18

TP = SP + VP
Total pressure (in inches, water gauge) 
Static pressure (in inches, water gauge) 
Velocity pressure (in inches, water gauge)

Question 19

Importance of airflow velocity

Answer 19

used to capture contaminants and overcome cross-drafts,
transportation of contaminants through the duct
balancing of the losses in the system
discharge of contaminant from the stack

Question 20

When using dilution ventilation - flow rate of fresh air is determined by

Answer 20

contaminant generation
proper mixing
target final concentration

Question 21

Parts of a local exhaust ventilation system

Answer 21

hood,
duct
air cleaning device
fan 
stack

Question 22

Canopy hood (local exhaust ventilation)

Answer 22

Used where hot gases and vapors are encountered workers do not work directly over source of emissions

Question 23

Capture velocity

Answer 23

minimum velocity of hood- induced air necessary to capture the contaminant

Question 24

Down draft hood

Answer 24

Used where contaminants heavier than air exist which are not being propelled away from the source of contaminant release
Draws air downward and away from the worker’s breathing zone

Question 25

Enclosure hood

Answer 25

Hood encloses the contaminant source and the air is forced in an opposite direction (upward, downward, or backward, away from the worker)

Question 26

Receiving Hood

Answer 26

Used at point of contaminant generation. - placed in close proximity to point of contamination generation

Question 27

Two types of hood openings

Answer 27

Flanged opening - have a lip, designed to create a certain desired airflow
Plain openings- air movement is directly into the duct

Question 28

Hood Entry Loss

Answer 28

represents the energy necessary to overcome the losses due to air moving through and into the duct

Question 29

Exhaust Ducts

Answer 29

Used to convey contaminated air from the hood to the air cleaner and/or stack

Question 30

Selection of exhaust duct size

Answer 30

based on minimizing friction loss, while maintaining an adequate transport velocity to keep particulate matter from settling out

Question 31

When two or more ducts branch out

Answer 31

Exhaust volume must be properly proportioned between branches by
balancing the two branches by the proper sizing of ducts and fittings to ensure proper distribution
or blast gates are are slide gates that can be pushed into the duct to partially block airflow to lower the amount of air entering into that branch

Question 32

Fans

Answer 32

generate the airflow volume of the system against airflow resistance presented by the system
axial or centrifugal

Question 33

Air cleaning devices

Answer 33

remove contaminant from teh air stream

Question 34

Ventilation Measurement Equipment

Answer 34

pitot tubes, rotating vane anemoometers, and thermal anemometers

Question 35

Pitot tubes

Answer 35

inserted into duct system and connected to a manometer, used to measure various pressures within the system

Question 36

Rotating vane anemometers

Answer 36

Used to measure airflow through large supply and exhaust systems
size should not exceed 5% of the cross-sectional area of the duct

Question 37

thermal anemometers

Answer 37

digital instruments that measure the heat removed by an airstream as it passes over a probe, which allows for calibration to the velocity of the air stream at a given density
must be perpendicular to the air stream and should be maintained in that position until the measurement is stabilized
probe is very fragile

Question 38

Pitot tube usage limited to velocities

Answer 38

at or below 600-800 fpm

Question 39

Most efficient fan blades

Answer 39

backward, curved