Industrial Exhaust

Question 1

What is face velocity?

Answer 1

It is a measurement of the average velocity at which air is drawn through the face to the hood exhaust

Question 2

How is face velocity varied in a conventional fume hood without a bypass?

Answer 2

By the sash opening

Question 3

What is the bypass intended to do in a conventional bypass fume hood?

Answer 3

Intended to address varying face velocities that create air turbulence leading to air spillage

Question 4

What is another name for an auxiliary fume hood?

Answer 4

Makeup air fume hood

Question 5

What is an auxiliary air fume hood (makeup air fume hood)?

Answer 5

It is a bypass hood with the addition of direct auxiliary air connection that provides unconditioned makeup air

Question 6

How many gauges heavier should hoods and elbows be compared to straight sections of connecting branch lines

Answer 6

Two gauges.

Question 7

True or false?

A VAV hood has a constant face velocity regardless of sash position

Answer 7

True

Question 8

Three types of workplace ventilation are?

Answer 8

-Indoor air quality ventilation (provides fresh conditioned air)
-dilution ventilation (blows clean air, exhaust dirty air)
-local exhaust ventilation (captures contaminants very close to source)

Question 9

Two common classes of hoods are?

Answer 9

Enclosing and capturing

Question 10

True or false?

Enclosed hoods capture the most contaminants but often interfere with work?

Answer 10

True

Question 11

True or false?

Capturing hoods are just as effective as enclosed hoods but provide more room for work to be completed?

Answer 11

False

Capturing hoods can only be located near the source of contaminants. Distance between face of hood and source must be short to effectively capture contaminants

Question 12

What is the recommended face velocity for a fume hood under normal conditions

Answer 12

100 FPM

Question 13

Ducting should be how many duct diameters straight before entering a fan?

Answer 13

2

Question 14

Two types of fans used for exhaust ventilation systems?

Answer 14

Axial fans and centrifugal fans

Question 15

Three types of fan wheels?

Answer 15

-Heavy material handling wheel
-material handling wheel
-air handling wheel

Question 16

How much straight ducting should there be on a fan discharge?

Answer 16

2.5D for velocities up to 2500 FPM and one diameter for every additional 1000fpm

Question 17

An exhaust should be located no more than how many feet to a buildings fresh air? And how far above roof line?

Answer 17

50’

10’

Question 18

True or false. You should use rain caps whenever possible on stacks?

Answer 18

False. They are ineffective at keeping rain out and they tend to force contaminants back into the building where they can be pulled into the fresh air intakes

Question 19

Where should clean outs on ducts be located?

Answer 19

Near elbows and junctions, on the sides or top of duct, spacing should not exceed 12’ for ducts measuring 12” diameter or less

Question 20

How should duct hangers and supports be spec’d

Answer 20

Enough capacity to carry the weight of the system being filled halfway with material. Hanger spacing should be according to SMACNA. And no more than 2D from joints and fittings

Question 21

Explosion doors should be constructed to what standard?

Answer 21

NFPA

Question 22

What are blast gates?

Answer 22

Used to isolate parts of the system that are not in use to save air, heat, or power

Question 23

Three types of longitudinal seams on round pipe?

Answer 23

-Grooved seam pipe lock
-butt welded seam
-spiral seam

Question 24

Can aluminum ducts be used? If so what constraints are in place?

Answer 24

Yes. Class 1 only and must be 2 gauges heavier than chart values

Question 25

What angle should branch runs enter the main trunk?

Answer 25

30-45 degrees (30 preferred)

Question 26

Branches should enter gradual expansions at what angle?

Answer 26

15-45 degrees (15 preferred)

Question 27

Transitions in main trunks and sub mains of duct should always be tapered. How much should it be tapered?

Answer 27

5 units long for every 1 unit increase. 5:1

Question 28

What three factors make respirators necessary to use

Answer 28

-ventilation is not feasible -when air contaminants are not lowered below acceptable limit -during emergency’s

Question 29

True or false. Exhaust systems only remove contaminated air from the building?

Answer 29

False in addition to removing air from the building they must discharge the air away from the building so it does not re-enter through fresh air

Question 30

Five factors for an efficient dust collecting system?

Answer 30

-hood design -conveying velocities -duct design and layout -balanced system -clean outs properly located

Question 31

True or false. Hoods should be located as close as possible to the source of dust contamination

Answer 31

True

Question 32

What is the best centreline radius for an elbow?

Answer 32

2.5 CLR

Question 33

How many classifications of industrial exhaust systems are there? What are they?

Answer 33

5 1-gases, vapours, fumes, mists 2-light dust, and powders 3-average industrial dust 4-heavy dust 5-corrosive fumes

Question 34

When exhausting air should makeup or replacement air always be considered?

Answer 34

Yes