ANKUR SHARMAMaster of Industrial Hygiene & SafetyBS-Plant Operations & Maintenancewww.ankur-mihs.blogspot.in
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Control of Work Control of Work EnvironmentEnvironment
Industrial Ventilation(a primary Engineering Control)
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.
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
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”
Generalized Diagram:--Methods of Control
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Desired control priority for chemical hazards
1.Source control
2.Pathway control
3.Receiver control
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
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.
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
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)
Natural Ventilation
Mechanical Ventilation
Preferred if significant health
hazards exist
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General or Dilution Ventilation
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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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
Zone of –ve pressure
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XRecommended
Practices
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The dilution ventilation must work with naturalair 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 ismuch more effective in diluting contaminants in the work zone.(Courtesy ExxonMobil Corporation.)
X
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
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.
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.
Face velocityAir 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
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
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
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
Direction of Air Movement
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X
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Selection of capture velocity
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
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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