Controlling airborne contaminants at work A guide to local exhaust ventilation (LEV)

This is a free-to-download, web-friendly version of HSG258 (Third edition, published 2017). This version has been adapted for online use from HSE’s current printed version.

You can buy the book at https://books.hse.gov.uk/ and most good bookshops.

ISBN 978 0 7176 6613 3 Price £20.00

This book provides guidance on the design of new local exhaust ventilation (LEV) equipment. It describes the principles of deciding on, designing, commissioning and testing effective LEV.

This guidance is written for employers who use or intend to use LEV. The HSG258 (Third edition) guidance will also help suppliers of LEV, managers, trade union and employee Published 2017 safety representatives. All of these groups need to work together to provide, maintain and use effective LEV and to reduce exposure from the inhalation of hazardous substances.

The book contains information about the roles and legal responsibilities of employers and suppliers; competence; principles of good design practice for effective LEV hoods and their classification; ducts, air movers; air cleaners; and system documentation – with checking and maintenance schedules and the marking of defective equipment.

It also includes guidance on the specification of LEV; commissioning; zone marking; the user manual and logbook; testing and hood labels.

This third edition has been updated and contains minor amendments and clarifications, but the advice is broadly unchanged and includes the updates made in the second edition based on feedback from industry.

London: TSO

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TSO@Blackwell and other Accredited Agents

Published with the permission of the Health and Safety Executive on behalf of the Controller of Her Majesty’s Stationery Office.

© Crown copyright 2017

First published 2008 Second edition 2011 Third edition 2017

ISBN 978 0 7176 6613 3

This information is licensed under the Open Government Licence v3.0. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/

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Printed in the United Kingdom for The Stationery Office.

J003398017 c3 11/17

This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory, unless specifically stated, and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance.

Contents Chapter 1 About this book 4

Chapter 2 Introduction to LEV, roles and responsibilities 6

Chapter 3 Properties of airborne contaminants 12

Chapter 4 Processes and sources 16

Chapter 5 Preparing a specification 21

Chapter 6 Hood design and application 27

Chapter 7 Designing the rest of the system 50

Chapter 8 Installing and commissioning 71 Chapter 9 User manual and logbook 80

Chapter 10 Thorough examination and test 84

Appendix 1 Legal requirements 92

Appendix 2 Selecting a ‘control benchmark’ and ‘control requirement’ 95

Glossary 99

Useful contacts 105

References and further reading 107

Further information 111

Chapter 1 About this book Introduction

1 Thousands of British workers contract occupational lung diseases such as occupational asthma and chronic obstructive pulmonary disease each year. Many people die or are permanently disabled by these conditions and are unable to work. People develop these diseases because they breathe in too much dust, fume or other airborne contaminants at work, often because control measures do not work well enough. Most industries are affected, including woodworking, welding, paint-spraying, stonemasonry, engineering and foundry work.

2 This guidance explains how local exhaust ventilation (LEV) can help employers effectively control exposure to gas, vapour, dust, fume and mist in workplace air by extracting the clouds of contaminant before people breathe them in. It describes the principles of design, installation, commissioning, testing and examination of proportionate ‘ventilation controls’.

Who is this book aimed at?

3 Where employers use or intend to use LEV they must ensure that it is appropriate for the task, installed and operated correctly and subsequently maintained so it continues to operate as when originally installed. Suppliers of LEV can play an important role in helping the employer with the design, installation and maintenance of the equipment. This guidance is therefore intended to help employers and suppliers as well as managers, trade union and employee safety representatives to work together to provide effective LEV so that workers are not breathing in hazardous substances. Different chapters will be more appropriate for different audiences.

4 HSE has evidence that employers are often unaware that their workers are being exposed to hazardous substances or that existing controls may be inadequate. The problems include:

˜˜ sources of exposure are missed; ˜˜ employers (and suppliers) are over-optimistic about the effectiveness of the controls; ˜˜ existing controls have deteriorated; ˜˜ the controls are not used correctly.

5 Suppliers can help employers by:

˜˜ assisting correct LEV choice; ˜˜ providing LEV that is fit for purpose, is shown to work and continues to work; ˜˜ questioning whether existing controls are working well enough.

6 Employers should have a systematic and critical approach to controls, working with designers, suppliers and employees to avoid expensive mistakes and control exposure effectively.

What does this book include?

7 This third edition has been updated, with minor amendments and clarifications, but the advice is broadly unchanged. It includes information on:

˜˜ LEV and other ventilation as part of the measures needed to control exposure; ˜˜ the roles and legal responsibilities of suppliers, employers and service providers, such as those who install, commission, maintain, examine and test LEV; ˜˜ the levels of competence people need; ˜˜ principles for design and/or supply of effective LEV, including matching the LEV to the process and the source; ˜˜ hood classification – enclosing, receiving and capturing; ˜˜ installation and commissioning; ˜˜ having a user manual and a logbook with every LEV system; ˜˜ information that the supplier should provide on checking and maintenance; ˜˜ a description of thorough examinations and tests.

8 There is also a glossary of useful terms and ‘Useful contacts’ and ‘References and further reading’ sections.

9 This book does not cover specialised topics such as biological agents; radioactive substances; pharmaceutical containment; confined spaces and air blowers; refuges (clean rooms in contaminated environments); or cleaning systems. However, the principles of LEV design often apply in such fields.

Chapter 2 Introduction to LEV, roles and responsibilities Key points

˜˜ The employer (the LEV owner) must ensure controls are adequate. ˜˜ Everyone in the LEV supply chain must be competent.

What is local exhaust ventilation?

10 LEV is an engineering control system to reduce exposures to airborne contaminants such as dust, mist, fume, vapour or gas in a workplace (Figure 1). Most systems, but not all, have the following:

Hood: This is where the contaminant cloud enters the LEV.

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

Air cleaner or arrestor: This filters or cleans the extracted air. Not all systems need air cleaning.

Air mover: The ‘engine’ that powers the extraction system, usually a fan.

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

11 All the components that may be part of the LEV system should be identified, for example:

˜˜ parts of equipment such as the machine casing or guards if they also serve as a component part of the extraction to control emissions; ˜˜ flues from hot processes, eg furnaces or ovens; ˜˜ systems to replace extracted air (make-up air), particularly where large ventilated booths extract large volumes of air from the workroom.

Roles and responsibilities

12 This book describes the principles of LEV design and application and this chapter describes the knowledge, skills and experience (‘competence’) required for each field of LEV practice (see Figure 2).

Employers

13 The employer is the ‘system owner’ and is the client for a new or redesigned LEV system. Employees, as process operators or ‘LEV users’, should make full and proper use of any LEV provided and report any faults.

Air mover

Discharge

Air cleaner Ducting

Hood

Inlet Figure 1 Common elements of a simple LEV system

LEV owner LEV supplier* LEV service provider*

Employer (client) Designer Commissioner

Employee (process Installer Maintenance engineer operator)

Employee (routine checks) Examiner

* Roles can overlap.

Figure 2 Who’s who in LEV supply and ownership

What employers should do before applying LEV

14 The employer must consider other control options and use them where appropriate (see HSE leaflets Working with substances hazardous to health1 and Clearing the air2) before applying LEV. In some circumstances, LEV may not be a reasonably practicable control as there may be many sources or extensive contaminant clouds that are too large for LEV alone to control. The other control options are:

˜˜ eliminate the source; ˜˜ substitute the material being used by something safer; ˜˜ reduce the size of the source; ˜˜ modify the process to reduce the frequency or duration of emission; ˜˜ reduce the number of employees involved with a process; ˜˜ apply simple controls to fully or partly enclose the process, eg fitting lids to equipment.

If LEV is appropriate, what employers should be aware of ˜˜ The key properties of airborne contaminants. ˜˜ How gases, vapours, dusts and mists arise. ˜˜ How contaminant clouds move with the surrounding air. ˜˜ The processes in the workplace which may be sources of airborne contaminants. ˜˜ The needs of the operators working near those sources. ˜˜ Whether LEV alone can provide adequate control or, if not, what additional control measures will be required. ˜˜ How to prepare a specification for the LEV designer. ˜˜ What to tell the LEV supplier.

15 When applying LEV employers should be aware of:

˜˜ the general principles of hood design and application; ˜˜ the need for airflow indicators and other instrumentation; ˜˜ capture zones, working zones and breathing zones; ˜˜ the general principles of ductwork, air movers and air cleaners and how they interact; ˜˜ the principles of how to discharge contaminated air safely and replace it with clean air; ˜˜ the process of installing and commissioning the LEV system; ˜˜ the usefulness of a user manual and logbook; ˜˜ the requirement for thorough examination and test of LEV.

16 The employer must use a competent person to provide ‘LEV services’. The competent person can be either an outside contractor or a competent employee of the LEV owner (the employer).

LEV routine checks

17 The people who carry out routine checks of the LEV system are usually employees or supervisors, but may be service providers.

These checks require understanding ˜˜ The parts of an LEV system and their function. ˜˜ How the LEV system should be used. ˜˜ How to recognise a damaged part. ˜˜ The simple checks that can confirm the LEV system is delivering its design performance and continuing to provide control as required and identified in the risk assessment and control strategy.

LEV suppliers and designers

18 LEV suppliers provide goods (an LEV system) and may then act as a service provider. Designers interpret the requirements of the employer and advise on an effective LEV system which is capable of delivering the required control.

What suppliers and designers should know ˜˜ Their role and legal responsibilities (see Appendix 1). ˜˜ How to liaise effectively with the employer and installer. ˜˜ Hazardous substances to be controlled. ˜˜ The principles of LEV hood design. ˜˜ How to apply hood design to the processes and sources requiring control. ˜˜ How to design LEV for ease and safety of checking and maintenance. ˜˜ The specifications for airflow, duct, filter, air mover, air cleaner, discharge, instrumentation and alarms. ˜˜ The specification for in-use performance checks. ˜˜ How to prepare an LEV user manual with schedules for maintenance and statutory thorough examination and test. ˜˜ How to prepare a logbook for the system, recording checks, replacing parts etc.

LEV installers 19 LEV installers work with commissioners (see paragraph 21) to ensure the equipment supplied provides adequate control of the contaminant. The installer may be the design company, a service provider, or even the employer (if competent).

What installers should know ˜˜ How to install LEV systems safely. ˜˜ The basic principles of LEV hood design and proper application. ˜˜ How to install according to the specified design. ˜˜ How to ensure LEV delivers intended performance. ˜˜ How to liaise effectively with the designer and employer.

LEV service providers

20 Service providers offer services such as installation, commissioning, maintenance and thorough examination and tests.

LEV commissioners

21 LEV commissioners work with installers to make sure the equipment supplied provides adequate control of the contaminant.

What commissioners should know ˜˜ Their role and legal responsibilities (see Chapter 8). ˜˜ How to liaise and communicate with the employer and employees. ˜˜ How to check that the LEV system is delivering its design performance. ˜˜ How to specify and describe the performance of the LEV system. ˜˜ How to check that exposure is effectively controlled and the LEV system is performing as designed. ˜˜ What to include in the LEV commissioning report as an adequate benchmark against which to compare future performance.

LEV maintenance and repair engineers

22 LEV maintenance and repair engineers are usually service providers, but sometimes an employee can carry out the work.

What maintenance and repair engineers should know ˜˜ How to recognise and assess hazards. ˜˜ How to follow safe systems of work. ˜˜ To warn operators that maintenance is under way. ˜˜ How the LEV system works. ˜˜ What assessment methods to use to check the LEV system’s performance is maintained. ˜˜ What routine maintenance is needed (following instructions such as those in a ‘user manual’). ˜˜ What measures of performance to record and who to report to if there are problems.

LEV examiners – statutory thorough examination and test

23 LEV examiners responsible for carrying out the thorough examination and test are usually service providers but this can be carried out by a competent person who could be an employee.

What examiners should know ˜˜ The parts of an LEV system and their function. ˜˜ The legal requirements for the thorough examination and testing of LEV systems. ˜˜ How to recognise a damaged part from a visual inspection. ˜˜ The purpose of, and how to use, the measuring and assessment instruments and techniques. ˜˜ The most suitable instrument to test the performance of each part of the LEV system. ˜˜ The standard to which each part of the LEV system should perform. ˜˜ How to recognise when a part of the LEV is performing unsatisfactorily, based on the measurements taken and assessment methods used. ˜˜ How to check whether the LEV is effective in reducing airborne contaminant emission and operator exposure. ˜˜ How to collate and record information in a clear, concise and usable way. ˜˜ How to work safely with the LEV plant and the hazards associated with it.

Legal responsibilities

24 People who supply, own and use LEV have legal duties.

˜˜ The employer of the people being protected by the LEV has legal responsibilities under the Health and Safety at Work etc Act 1974 (the HSW Act),3 the Control of Substances Hazardous to Health Regulations 2002 (as amended) (COSHH)4 and the Management of Health and Safety at Work Regulations 1999 (MHSWR).5 There are also special provisions for employers in safety data sheets under REACH6 (see paragraphs 82–86). ˜˜ LEV suppliers have legal responsibilities under the HSW Act and the Supply of Machinery (Safety) Regulations 2008 (SMSR),7 including ‘essential health and safety requirements’.

˜˜ If an employer is using a substance that could form an explosive atmosphere they must consider their responsibilities under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR),8 and the supplier of equipment for use in an explosive atmosphere their responsibilities under the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996. ˜˜ Service providers have legal responsibilities under the HSW Act and the Construction (Design and Management) Regulations 2015 (CDM 2015).9

25 For more about legal responsibilities, see Appendix 1.

Competence

26 Another legal requirement under MHSWR and COSHH is ‘competence’. This means people having sufficient training, knowledge and experience to carry out the job they are employed to do. Competence requirements apply to whoever:

˜˜ designs or selects control measures; ˜˜ checks, tests and maintains control measures; ˜˜ supplies goods and services to employers for health and safety purposes.

27 The requirement for competence for suppliers of goods and services means that the extent and depth of their knowledge and capability must be sufficient to assess and solve the problems they are likely to meet.

28 The more complex a control scenario is and the more serious the results of failure, the greater the degree of competence required. For example:

˜˜ Simple, routine, specified work requires basic knowledge and training. ˜˜ Complex work requires recognised and appropriate qualifications, much greater knowledge and demonstrated success at applying this knowledge to a variety of problems.

29 Many trades recognise levels of competence based on qualifications and tests of capability, as well as experience of successful problem-solving over a number of years. See Appendix 1 for more information on becoming ‘competent’.

30 The employer decides who to employ or consult and needs to be an ‘intelligent customer’ to get the best result. HSE has produced simple guidance to help the employer choose a supplier when they are considering installing LEV (see HSE leaflet Clearing the air). Suppliers need to prepare their information to respond to this approach.

Training courses

31 Those individuals wishing