Industrial Ventilation-Introduction

ANKUR SHARMAMaster of Industrial Hygiene & SafetyBS-Plant Operations & Maintenancewww.ankur-mihs.blogspot.in

ISTAR, SPU VVN Anand

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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

ISTAR, SPU VVN Anand 13

XRecommended

Practices



The dilution ventilation must work with naturalair movement such as the convective rise due to solar heat load on this process vessel.


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


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


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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Industrial Ventilation-Introduction

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