[PDF] Local Exhaust Ventilation (LEV) Guidance

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Local Exhaust Ventilation

(LEV) Guidance

Our vision:

A country where worker

safety, health and welfare and the safe management of chemicals are central to successful enterprise

Published in January 2014 by the Health & Safety Authority, The Metropolitan Building, James Joyce St., Dublin 1.

Contents

Chapter 1

Summary ...............................................................2

Chapter 2

Introduction ............................................................4 Risk Assessment.....................................................5

Chapter 3

What is Local Exhaust Ventilation (LEV)?..................................7

Chapter 4

Types of Local Exhaust Ventilation (LEV).................................19

Chapter 5

Misconceptions ........................................................31

Chapter 6

Properties of Airborne Contaminants ...................................35

Chapter 7

Flow Rates .............................................................38

Chapter 8

How to Select Local Exhaust Ventilation (LEV)...........................40

Chapter 9

Installation and Maintenance of LEV ....................................43

Chapter 10

Information and Training for Employees ................................47

Chapter 11

Keeping Records .......................................................49

Chapter 12

Examining & Monitoring Performance ..................................50

Chapter 13

Main Legal Requirements...............................................57

Chapter 14

Standards ..............................................................61

Chapter 15

References .............................................................62

Chapter 16

Further Reading........................................................63

Chapter 17

Useful Contacts ........................................................64

Chapter 18

Drawings/pictures/diagrams courtesy of the HSE/HSL UK & IOSH

2Chapter 1

This guidance is written for employers, managers, employees and their safety representatives and those who provide, install and maintain local exhaust ventilation (LEV) systems. In preventing exposure to harmful substances in the workplace, there is a hierarchy of control measures that must be considered, commencing with the elimination or substitution of the hazard or, where these options are not possible, the hazard must be controlled by engineering means. Local exhaust ventilation (LEV) is one such engineering control measure. LEV is an engineering system designed to reduce employee exposure to airborne contaminants (dust,

mist, fume, vapour, gas) in the workplace by capturing the emission at source and transporting it to a

safe emission point or to a lter/scrubber. Employers need to work with designers, suppliers, installers

and employees to eectively control exposure to airborne contaminants. Suppliers must provide LEV that is t for purpose, is shown to work and continues to work. The employer (the LEV owner) must ensure controls are adequate. Everyone, including suppliers and users of the LEV, must be competent in the use of the LEV system.

The main LEV elements are:

A hood of some kind, where the contaminants enter the system Ducting, which safely transports the contaminants to a lter/cleaner/exhaust point

Air cleaner/lter/scrubber

Air mover: a fan to power the system

Discharge: a safe point of air exhaust

When using LEV to control exposure, the employer must thoroughly assess the hazards to be controlled and be satised with the following: the LEV system is t for purpose; it is being used

correctly by trained employees; the system is regularly maintained to remain eective; and records are

kept to demonstrate the system is both eective and ongoing.

Having a good understanding of what

hazards need to be controlled is crucial to ensure that the initial design is capable of achieving adequate control.

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Local Exhaust Ventilation (LEV) Guidance

Chapter 1

Summary

When installing LEV:

Identify and assess the hazard(s) to be controlled Identify competent contractors to install the system Provide the installer with clear requirements or specications Review and ensure that the design and its specications are satisfactory Obtain and retain all the related paperwork in design specications, including the commissioning report (hand book) Ensure when the system is installed that it meets the design specications Maintain the system and measure performance regularly

Train employees in the proper use of the LEV

3Chapter 1

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Local Exhaust Ventilation (LEV) Guidance

Chapter 2 Introduction

Local exhaust ventilation (LEV) is an engineering system frequently used in the workplace to protect employees from hazardous substances. To have an eective system it is important that it is well

designed and installed, used correctly and properly maintained. All the participants, from designer to

end-user need to work together to provide an eective system.

Common Problems

Employers are often unaware their employees are being over-exposed to hazardous substances or that existing controls may be inadequate

Sources of exposure are missed

Employers (and suppliers) are over-optimistic about the eectiveness of the controls

Existing controls have deteriorated

Controls are not used correctly

Employers need to work with designers, suppliers and employees to ensure eective control, to avoid expensive mistakes and to control exposure eectively. Suppliers must provide LEV that is t for purpose, is shown to work and continues to work. The employer (the LEV owner) must ensure controls are adequate. Everyone, both suppliers and users of the LEV, must be competent in the operation of the LEV system. Adverse health eects can occur when employees are exposed to occupational hazards such as dusts, fumes and vapours (chemical or biological agents). The eects of exposure to a hazard depend on the frequency, duration and degree of exposure: some substances can cause immediate health eects, such as carbon monoxide poisoning; others, such as asbestos, can have a long latency period. The

potential for exposure to any chemical or biological agent needs to be assessed in each place of work.

Employees can contract occupational illnesses and diseases and develop these because they breathe in too much dust, fumes or other airborne contaminants at work, often because control measures are not in place or do not work well enough. Many industries can be aected, including chemical processing, pharmaceutical, biotechnology, woodworking, welding, paint-spraying, stonemasonry,

engineering and foundry work. The purpose of this guidance is to describe how to control gas, vapour,

dust, fume, mist, in other words aerosols (hazardous agents), in the workplace air by using local exhaust ventilation (LEV), i.e. extracting the contaminant and preventing exposure.

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4Chapter 2

Although this guide concentrates on local exhaust ventilation (LEV), it is important to remember that

the control or lack of general ventilation, including general supply and exhaust ventilation, can aect

the performance of the LEV. For instance, a draught from an open door may challenge a welding hood extraction performance, or an insucient supply of air in a closed system will 'starve' an exhausting LEV system. Therefore there are many factors that need to be considered when installing controls.

Risk Assessment

A risk assessment involves (1)

anticipating; (2) recognising; (3) evaluating; and (4) controlling the hazards to which the employee might be exposed. The Authority has advice on its website (www.hsa. ie) on how to carry out an assessment. When the employer has completed a risk assessment, evaluated the risks and determined the potential hazards, control methods need to be considered. As well as health hazards, there may be ammability, reactivity and/or physical hazards (e.g. excessive heat).

Control

When control is being considered there is a standard hierarchical approach. Can the process be changed so that the hazardous chemical agent can be eliminated or substituted with a less hazardous one? Can the process be modied to reduce risk of exposure (for example can the process temperature be lowered to reduce vapour release)? Are engineering controls appropriate? Can

structures such as hoods, booths, enclosures or local exhaust ventilation be used to contain or capture

hazardous chemical agent emissions?

Administrative controls

are used to minimise employee exposure by time planning and rotation. The nal control in the hierarchy is the use of personal protective equipment (PPE)

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Local Exhaust Ventilation (LEV) Guidance

5Chapter 2

In installing controls, the employer should start at the top of the hierarchy before rushing to install

local exhaust ventilation (LEV), for example. The employer must rst determine what is the most eective controls measure(s). The installation of any control measure is likely to be expensive (it has, for example, the potential to introduce operational diculties), so a thorough review of the eectiveness of the chosen control method and how employees will interface with the system is vital.

The LEV system must be t for purpose. For example, where the process entails grinding, it is likely that

dust will be propelled from the source and the system needs to be designed to contain and capture

the fugitive dust. Before designing or installing an LEV system, a good understanding of contaminants

and the process demands are necessary. Consideration should be given as to whether the system will be required to cope with changing materials processes and, if so, whether you need to build in exibility for this from the start. The installation of new engineering controls such as LEV may bring its own risks and should be included in the overall assessment of operations. How well does the LEV system interface with the employee, the process and the place of work? For example, the noise generated by new fans/motors may need to be considered to prevent over-exposure to noise in the workplace; manual handling or ergonomic diculties may be introduced; it may result in the generation of static electricity because of material type; or lack of bonding/earthing may be an ignition source.

Once the system is installed as designed, it must be used correctly and not tampered with; it must be

regularly performance checked so that its eectiveness in protecting the employee(s) is achieved and must be maintained as laid down in the risk assessment. In some circumstances, such as woodworking machines, the LEV may be designed as an integral part of the equipment. Therefore, although the design stage is completed in advance, employee training must be applied in all other elements, such as proper use, cleaning and maintenance.

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Local Exhaust Ventilation (LEV) Guidance

6Chapter 2

Chapter 3 What is Local Exhaust Ventilation (LEV)? In its simplest terms local exhaust ventilation is an engineering system to protect employees from exposure to hazardous substances by containing or capturing them locally, at the emission point. Local exhaust ventilation (LEV) is only one of many engineering control options that may be used to remove and prevent employee exposure to vapour, mist, dust or other airborne contaminants. To be eective in protecting the employee(s), it is important that it is of good design , is ?t for purpose is regularly maintained and the system"s performance is monitored . Failure to do so can lead to employees being exposed because they have the impression that the system is eective when it is not. Poor design and/or maintenance may lead, for example, to leakage in the workplace, causing concentrated local exposure rather than preventing it. A poorly designed, installed, misused and incorrectly maintained system can become an expensive waste of expenditure and may give a false impression of hazard control.

Employees must be given

training in its use and maintenance to understand its correct use and eectiveness. Many employers and employees overestimate the eectiveness of the dierent types

of LEV, and have a poor understanding of the types of conditions that could lead to a reduction in or

depletion of the LEV"s eectiveness.

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7Chapter 3

Good design and t for purpose

Good design and being t for purpose are the crucial initial considerations to ensure the eectiveness of the system. Where the process changes and additions or changes are needed the overall design should be reconsidered so the system remains eective. Creeping additions and extensions of the system can be a temptation for expediency, but lead to totally ineective systems. If a system is redesigned, it also needs to be re-commissioned.

Examples of poor design:

The extract fan system is sized too small and the hood cannot contain or capture the contaminants. The fume hood is placed in an area where there is sporadic cross draughts or insucient supply air and the inward ow is challenged. A hood may have been designed without proper consideration of the work being done; the t is incorrect and it may be impossible for the employee to use the system eectively; it may introduce ergonomic or manual-handling hazards.

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Local Exhaust Ventilation (LEV) Guidance

8Chapter 3

Local Exhaust Ventilation Users

Supplier & Designer, Installer

& CommissionerEmployers/Supervisors/

Operators

Maintenance & Repair

EngineersPerformance & Examination

Competent Persons

Local Exhaust

Ventilation (LEV)

Participants

Local Exhaust Ventilation Users

Supplier & Designer, Installer

& CommissionerEmployers/Supervisors/

Operators

Maintenance & Repair

EngineersPerformance & Examination

Competent Persons

Local Exhaust

Ventilation (LEV)

Participants

A fan may be incorrectly placed so that a major section of the ducting is under positive pressure. Where this ducting is within the workplace, any leakage on the positive pressure side has the potential to expose employees who may or may not be involved in the process and may be unaware of their exposure. Where ducting is wrongly sized, the transport velocity within the duct may be insucient and contaminant will settle out in the ducting. This can be a serious re hazard if combustible or ammable contaminants are being extracted. Flammable vapours/materials are being extracted but no consideration has been given to the prevention of a source of ignition or to dilution well below the lower explosion limit. Poor design of exhaust point may cause the contaminants to be captured by the air supply system; for example, instead of being exhausted and diluted, they may enter a downdraught caused by adjacent buildings and re-enter the workplace.

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Local Exhaust Ventilation (LEV) Guidance

9Chapter 3

Elements of LEV system:

Most systems have the following ve elements:

1. An inlet/enclosure/hood where the contaminant is captured or contained and enters the LEV.

2. Ducting: This conducts air and the contaminant from the hood to the discharge point.

3. Air cleaner or lter: This lters or cleans the extracted air. Not all systems need air cleaning.

4.

Air mover:

The fan and motor that powers the extraction system.

5. Discharge or exhaust: This releases the extracted air to a safe place.

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10Chapter 3

HoodContaminant

Ducting

Fan

ExhaustAir cleaner

The unit in its entirety must be of good design.

For example:

Leak-proof: leakage on the suction or negative pressure side of the air remover will lead to inecient extraction and leakage on the positive pressure side and may reintroduce the contaminant to the workplace. The ow rate of air through the system must be sucient to achieve the initial capture/ containment and carry all contaminants to the purifying/ltering system (transport velocity). Combustible dusts (wood dust, for example), if not extracted properly, can deposit in the ducting and be a re or explosion risk. Flammable solvents being captured by the system need to be diluted by sucient air ow to prevent the formation of a ammable mixture. The ducting needs to be structured so as to avoid eddy currents and inecient ow. For example, it should not have sharp right-angled turns, as this leads to dead areas with no ow. The construction and materials of construction need to be compatible with the contaminants being extracted. For example, where ammable gases or vapours are being extracted, the system should not be able to generate a source of ignition. Likely ignition sources could arise from the use of non-rated electrical equipment such as the air mover, or from the accumulation of static electricity from the lack of earthing and bonding and the use of non-conductive materials. Corrosion by the contaminants is another consideration.

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11Chapter 3

1. An Inlet/Enclosure/Hood includes some type of hood or enclosure such as those listed below:

a. cowl for capturing welding fumes b. laboratory fume hood or cupboard c. biological safety cabinet d. paint-spray booth e. down-ow booth f. ventilated hopper g. dust-capturing device at woodworking machine h. pouring station i. movable/exible hoods j. portable hoods with lters k. abrasive blasting room or cabinet

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12Chapter 3

The three basic types of hood:

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13Chapter 3

EnclosingReceivingCapturingHOOD

Air jet

Full enclosure

‘Room" enclosure

Canopy

Push-pull system

Rim or lip extraction

Downdraught table

Low volume high velocity

(LVHV)

Simple capturing hood

Other receiving hoods

Partial enclosure - booth

Moveable

source and hood The type of hood or enclosure is inuenced by the work being done. The hood or enclosure should not obstruct or cause ergonomic diculties (e.g. manual-handling limitations or over-reaching). The hood/enclosure may need to be designed to capture/contain dust, fumes, mist, bres, vapour or gas aerosols. The contaminant cloud or aerosol may be a slow release or a highly energised release caused by a power tool, for example. Dusts from solids being dropped can temporarily overcome a system. The degree of containment around the emission point is crucial. The hood should be structured and placed at the emission point so as to entrain/contain the emission. For example, the air-ow rate to a circular extraction duct with no hood attached will fall to about 10% of the in-duct ow rate at one diameter distance from the duct opening.

As the distance of the emission point from

the hood increases, the LEV eectiveness decreases dramatically.

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14Chapter 3

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