This document discusses industrial ventilation as a primary method of controlling the work environment. It defines ventilation as supplying or removing air using natural or mechanical means. The purposes of industrial ventilation include diluting airborne contaminants, preventing hazardous dispersal, preventing fires/explosions, and creating a comfortable work environment. The types of ventilation discussed are general dilution ventilation, local exhaust ventilation, and heating, ventilation, and air conditioning systems. Local exhaust ventilation is usually the preferred method as it captures contaminants at their source.

1. ANKUR SHARMA
Master of Industrial Hygiene & Safety
BS-Plant Operations & Maintenance
www.ankur-mihs.blogspot.in
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Control of WorkControl of Work
EnvironmentEnvironment
Industrial Ventilation(a primary
Engineering Control)

2. Work Environment Control…..
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To prevent or minimize exposure of workers
to harmful environmental hazards which
could lead to serious occupational illnesses
and diseases or even death.

3. Hazards of Poor or No Ventilation
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Lack of oxygen (headache, fatigue, Asphyxiation,
particularly in confined spaces)
Excessive heat, cold, and humidity
Toxic fumes (e.g.- Lead, cadmium, zinc)
Toxic vapors (e.g.- Benzene, toluene, TCE, MEK)
Toxic gases (e.g.- Hydrogen Sulphide, ammonia)
Dusts (causing poisoning or gradually reduced lung
capacity)
Fire/explosion

4. Control philosophy
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“The correct recognition and careful
evaluation of the hazards are extremely
important and will constitute the basis of
appropriate control measures”

5. Generalized Diagram:--
Methods of Control
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Desired control priority for chemical hazards
1.Source control
2.Pathway control
3.Receiver control

6. Pathway Controls
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Pathway controls generally are not as desirable as
source controls:-
Exposures are reduced, but not eliminated (general
ventilation)
The source hazard still remains
Pathway controls often are costly
Operation cost ↑
Pathway control systems must be maintained

7. Industrial Ventilation
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 Ventilation is a primary engineering control available
to eliminate or reduce the concentration of gases,
dusts, vapors, smoke, and fumes present in the work
environment .
 Ventilation is defined as the process of supplying air
to, or removing air from, any space by natural or
mechanical means.

8. Purpose
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 To dilute airborne contaminants to acceptable levels
 To prevent hazardous air contaminants from
dispersing into the working environment (LEV)
 To prevent fire and explosion
 To create a comfortable environment in the plant -
i.e. The HVAC system

9. Types of Ventilation
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General Dilution Ventilation(Pathway control)
- Mechanical Ventilation (involves Fans)
- Natural Ventilation(with natural air movement caused by thermal gradient or any other)
Local Exhaust Ventilation (Source control)
Heating Ventilation and Air conditioning System (to
control temp. & humidity)

10. Natural Ventilation Mechanical Ventilation
Preferred if significant
health hazards exist
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General or Dilution Ventilation

11. Clean Air
Supply
Zone of Contaminant
Release
Operators Breathing
Zone
Discharge
Opening
Direction of air flow must remove contaminants from workers
breathing zone
Principle of General Ventilation
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12. Blowing and Exhausting
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Approx 10% of the face
velocity at 30d away from
Pr. Jet Opening
Approx 10% of the face
velocity at 1-dia. away
exhaust opening
4000 FPM
4000 FPM
400 FPM
400 FPM

13. Zone of
–ve pressure
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14. X
Recommended
Practices
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The dilution ventilation
must work with natural
air movement such as
the convective rise due
to solar heat load on
this process vessel.

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Short circuiting (top) reduces
the effectiveness of dilution
ventilation.
Relocating the fan and make-
up air entry ports can help to
solve the problem.
X

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An exhaust fan cannot direct
airflow (top).
The same fan system blowing air
(bottom) can direct airflow, and is
much more effective in diluting
contaminants in the work zone.
(Courtesy ExxonMobil Corporation.)
X

18. General Dilution Ventilation
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 If (TLV <100ppm)- not recommended
 Only suitable for contaminant with low & uniform generation rate
 Not completely remove the contaminant
 Some general ventilation devices:---
Industrial
exhaust fansRoof-mounted exhaust fans

19. Local Exhaust Ventilation-Source Control
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Capture or contain contaminants at their source
Typical Local Exhaust
Ventilation system
Components of Local
Exhaust SystemDuct

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Hoods - any point where air is drawn into the
ventilation system to capture or control contaminants.
Ducts - the network of piping that connects the
hoods and other system components.
Fan - air-moving device that provides the energy to
draw air and contaminants into the exhaust system &
through the ducts and other components.
Air Cleaner - a device to remove airborne
materials that may be needed before the exhaust air is
discharged into the community environment.

21. LEV system is usually preferred control
method, if:
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 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.
 Emission sources are near the workers' breathing
zones.

22. Face velocity
Air velocity at the hood
or slot opening
Ventilation Terminology
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Capture Velocity - Air velocity at any point in
front of the hood necessary to overcome opposing
air currents and to capture the contaminant at
that point causing it to flow into the hood
- Important hood/process design criteria

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Effect of Side Baffles

24. Hood Proximity(Location) & Exhaust Volume
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To maintain desired capture velocity,
------locate hood as close to source as possible
Q=V(10X2
+A)
↑es
required
(Q)flow rate
& associated
costs

25. Use of Enclosures
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-- ed power consumption↑
-- less collection efficiency
-- ed flow rate to have↑
sufficient capture velocity
-- more collection efficiency
--less flow rate required
--less power consumption

26. Benefits of ENCLOSURES
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Using techniques such as enclosures,
control capabilities are maximized
Air volumes requirements are drastically
minimized
Reduces required make-up air and
associated costs

27. Direction of Air Movement
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X

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Selection of capture velocity

30. Testing Ventilation Systems
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Ensure it meets design criteria
Comply with regulatory standards
Determine system balance
Determine if maintenance or repair require
Determine whether existing system is capable of
handling additional hoods

31. Reference
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• Industrial Ventilation ( A manual of Recommended Practice, 22nd
Edition-1998)
• Fundamentals of Industrial Hygiene (5th Edition) by Barbara A Plog (Part-5(control of Hazards))
• http://www.epa.gov/eogapti1/bces/module5/hoods/principle/principle.htm
• www.hse.gov.uk/pubns/guidance/ocm2.pdf
• www.hse.gov.uk/lev/
• www.hse.gov.uk/lev/faqs.htm
• www.coshh-essentials.org.uk/assets/live/G200.pdf
• http://www.ccohs.ca/oshanswers/prevention/ventilation/introduction.html
• www.ohsl.co.uk/local-exhaust-ventilation.php
• http://www.ohsl.co.uk/local-exhaust-ventilation.php

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