TR19

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Specialist Groups

Building & Engineering Services Association Esca House, 34 Palace Court, London W2 4JG T 020 7313 4937 www.b-es.org

GUIDE TO GOOD PRACTICE

Internal cleanliness of ventilation systems (TR19)

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GUIDE TO GOOD PRACTICE

Internal cleanliness of ventilation systems TR19 2nd_{Edition | October 2013}

Building & Engineering Services Association

Acknowledgement

B&ES records its appreciation and thanks to the many persons and

organisations who have freely given information on various aspects of this work, in particular to the following members of the Ventilation Hygiene Group Branch and Ductwork Technical Sub-Committee, who contributed unstintingly of their knowledge and experience to this later edition: Craig Booth Paul Downing Alan Gregory Gareth Keller Steve Lorriman Jim Murray Gary Nicholls Richard Norman Nick Tregaskes Peter Reid

Special thanks are offered to J Bridges for his assistance in the development of the Deposit Thickness Test, and to T Mulhall of the HSE.

ISBN 0 903783 35 5

Publishing history:

First published as DW/TM2 (1991) and TR/17 (1998) Second Edition (2002) and TR/19 (2005 and 2013)

Building & Engineering Services Association Esca House 34 Palace Court London W2 4JG T: 020 7313 4900 [email protected] www.b-es.org

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Foreword

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1 Introduction

1.1 The internal cleanliness of ventilation systems is considered important for human comfort and health, energy consumption, system service life and for cleanliness of operations or processes carried out in the ventilated area.

1.2 The guiding principle of this document is that a defined, measurable level of cleanliness should be achieved. In cases of doubt regarding procedures, facilities and methods to achieve cleanliness then this principle defines success or failure.

The first edition of TR/17 established a level of particulate cleanliness verification for both new and existing ventilation systems and an indication of when it is considered appropriate to clean systems in use. The second edition was expanded to include an enlarged section on kitchen extract systems. It established levels of grease surface deposit at which it is appropriate to clean a kitchen extract ventilation system and at which post-clean verification is achieved. The 3rd

publication TR/19 incorporated both TR/17 and the former DW/TM2 – Guide to Good Practice Cleanliness of New Ductwork Installation. This included revised guidelines to ensure that new ductwork systems remained protected during the installation period and prior to

commissioning.

This current TR/19 (second edition) now updates guidance on surface cleanliness testing and includes reference to the new British and European Standard BS EN 15780 Cleanliness of Ventilation Systems which was introduced during 2011.

Also in this edition significant changes have been made to highlight the current best practice for ensuring that kitchen extract systems are maintained to minimise the risk of fire associated with grease accumulation.

1.3 This Guide places a responsibility on the designer to clearly state if

verifiable cleanliness is required for newly installed ductwork.

1.4 When specifying or agreeing cleanliness criteria on newly installed or

existing ducting it is important that all interested parties clearly agree on the cleanliness quality class of each ventilation system as defined by BS EN 15780 (see section 5.14 of this Guide) as each of these classes has a different acceptable levels of dust accumulation.

1.5 Previously legislation and guidance on standards in buildings has

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associated systems. The proper maintenance of building systems is also recognised as crucial to the health, economic and safe operation of occupied spaces.

1.6 The Workplace (Health, Safety and Welfare) Regulation 1992 requires

that effective provision should be made to ensure that every enclosed workplace is ventilated by a sufficient quantity of fresh or purified air. Where this ventilation is provided by mechanical means the

regulations required those mechanical ventilation systems to be maintained (including cleaned as appropriate) in efficient working order. Failure to carry out these duties is a breach of the Regulations. (Please see Appendix B for further reference.)

The Corporate Manslaughter and Corporate Homicide Act 2007 places a much greater corporate responsibility and business risk on

organisations in terms of the consequences of health and safety compliance failure, particularly where inadequately cleaned systems heighten the risk of fire and fire spread.

1.7 General ventilation systems (not affected by kitchen grease) as

defined, and referred to in this Guide include, but are not limited to, the following:



Ductwork



Air handling units



Fan coil and induction units



Constant air volume units



Variable air volume units



Control dampers



Attenuators



Air terminals



Ancillary components associated with the air distribution system.

1.8 Kitchen extract systems as defined and referred to in this Guide

include, but are not limited, to the following:



Canopy



Canopy/extract plenum



Ductwork



Fans

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

Ancillary components associated with the extract system Other extraction systems that may be affected by grease/oil deposits, eg dish wash, pot wash, general kitchen extract ventilation



Fire dampers (where fitted) and attenuators.

Inadequate access to kitchen extract ducting has been shown to be a contributory factor to fires that spread through ducting. The designer therefore has a responsibility to ensure that adequate access is

possible both through the building fabric to and into the system; thus ensuring that planned preventative maintenance (“PPM”) for full grease removal is practicable. The designer is advised to seek guidance from a specialist cleaning contractor at the design stage. Section 7 (specific considerations for kitchen extract systems) can be read separately for the convenience of readers solely interested in this aspect of the cleanliness of ventilation systems.

1.9 Table 1 (typical application of system quality classes) is applicable to

all systems except kitchen extract systems (which are dealt with in Section 7) and defines the levels of dust deposit at which it is

appropriate to clean a general system. The levels of deposit referred to in Table 8 relate to normal nuisance dust and are based on good practice as well as the British and European standard BS EN 15780. Table 13 defines the level of grease deposit at which it is appropriate to clean a kitchen extract system and is again based on fire safety good practice.

1.10 A level of cleanliness is detailed which would verify acceptable

cleaning performance for general and kitchen extract systems.

1.11 Measurement methods within this Guide do not apply to

microbiological contamination or hazardous materials, such as lead, asbestos, toxic process dusts, etc. Where such materials or

contamination are present, specialist advice should be sought.

Appendix A gives general information on microbiological contamination. More detailed advice is given in TM26:2000 published by CIBSE (see Appendix E).

1.12 For convenience, two quick reference guides have been included at

Appendix E and F, which give a summary of cleaning frequencies and dust/grease accumulation levels for air ductwork and grease extract systems.

1.13 The onus is on the specifier/client to select and clearly define any

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eg verification responsibility and which ventilation systems and plant are to be included (refer to Section 4). The following items should be specifically quantified:



Any component to be replaced (eg, filter, media, flexible ductwork etc)



Items requiring repair or remedial attention (eg, damaged or corroded ductwork or fittings)



Re-commissioning or testing requirements.

Alternatively, contingency sums should be considered.

Appendix C gives advice on the selection of specialist contractors.

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2 Protection, delivery and installation standards for

maintaining the internal cleanliness of new ductwork

prior to commissioning and/or handover

Introduction

2.1 With the introduction of BS EN 15780 all interested parties should be

made aware that there are now three classifications of system types with regard to internal duct cleanliness. The document gives

guidance on the system quality class for each of these types of areas (see table 1 below) and the most applicable should be agreed

between the installer/building owner and other interested parties prior to the commencement of installation. This British Standard requires a verifiable cleanliness standard to be achieved prior to handover. Acceptable dusts accumulation levels for new ductwork are shown in table below (table 2).

Table 1 Typical applications of system quality classes

System quality class Typical examples

Low Rooms with only intermittent occupancy, eg storage rooms

Medium Offices, hotels, restaurants, schools, theatres, residential homes, shopping areas, exhibition buildings, sport buildings, general areas in hospitals, general working areas in industries High Laboratories, treatment areas in hospitals, high

quality offices

Table 2 Acceptable dust accumulation levels in new ductwork

Cleanliness quality class

Acceptable dust accumulation level Supply, recirculation or secondary air ductwork Acceptable dust accumulation level Extract ductwork Low <0.9 g/m2 _{<1.8 g/m}2 Medium <0.6 g/m2 _{<1.8 g/m}2 High <0.3 g/m2 _{<0.9 g/m}2

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2.2 Section 2 is a replacement for the former HVCA publication DW/TM2 Guide to Good Practice Internal Cleanliness of New Ductwork

Installations. In order to reduce the risk of contamination, DW/TM2 dealt with the level of protection afforded to new ductwork during manufacture, transit to site, on-site storage and installation. It did not provide or make reference to any measurable level of cleanliness. It was the frequent failure of specifiers to recognise this point that gave rise to ‘contractual’ disputes as to whose responsibility it was not only to provide a suitable working environment but also if the ductwork became contaminated.

2.3 Since DW/TM2 was first published in 1991, both clients and Health &

Safety legislation have increasingly demanded greater levels of internal cleanliness not only in existing systems, but also in newly installed ductwork. The publication by HVCA of TR/17 in 1998 provided, for the first time, a measurable level of cleanliness of ventilation systems. However, the practice was that some specifiers were applying DW/TM2 when they should have been using TR/17. In 2005 it was decided to withdraw DW/TM2 from circulation in favour of incorporating a revised version of its contents into this all-inclusive Guide to Good Practice Cleanliness of Ventilation Systems - TR/19. At the same time opportunity was taken to update the advice given in the former DW/TM2.

2.4 Section 2 offers Protection, delivery and installation (PDI) levels 1

and 2 to replace the original DW/TM2 categories of BASIC and INTERMEDIATE as it is considered, that with the advent of specialist cleaning, the factory sealing of ductwork associated with the former ADVANCED Level of Protection in DW/TM2 is no longer necessary. This is not only due to the adverse site conditions that can exist during installation but also the advent of a more definite approach to on-site specialist cleaning and the greater demand for on-going building services maintenance programmes. It is recognised that some sites may be able to guarantee a dry and clean working environment /area and clause 2.18.1 highlights the additional considerations that may be required to offer protection of the ductwork during transportation and site storage.

Air movement devices and in line plant and equipment

2.5 The scope of this Guide does not cater for the protection and

cleanliness of in-line equipment including air handling units, filters, attenuators, fans and terminal units or for the transfer of dust and dirt into the duct system from such plant.

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2.6 The specification for plant and equipment must ensure that the internal

cleanliness, protection and storage of the equipment should be compatible with the levels of cleanliness specified for the ductwork.

Notes for designers and specifiers

2.7 This section defines standards for the delivery, installation, protection

and cleanliness of new ductwork with the emphasis on there being a reasonable and practical approach to the exclusion of dust and foreign matter. In addition to Sections 2.8 to 2.13 that follow, the designer/specifiers attention is particularly drawn to Sections 1.4, 2.5, 2.16, 2.18.1 and 2.18.2.

2.8 These guidance notes apply to ductwork constructed in accordance

with the latest B&ES standards.

2.9 Practical experience shows that due to the various activities that

typically occur on construction sites, there is a risk that the installed ductwork will not avoid dust contamination regardless of any

measures of protection employed.

2.10 Whilst capping off will help to minimise the ingress of dust and

foreign matter, the only certain way to ensure cleanliness on final handover is to employ a specialist cleaning contractor. A measurable level of cleanliness is defined in Section 9 of this Guide.

2.11 It should be noted that the specified level of protection can only be

achieved if the working environment is compatible. For certain levels of protection, the installation of the ductwork may not be possible until the construction work has reached an advanced stage. Factory and site sealing of ductwork and/or its open ends may be wasteful if ductwork is installed, subjected to or left in a dust laden atmosphere. Under such circumstances, natural air movement through the

ductwork and its temporarily exposed openings will inevitably result in the ingress of dust into the ductwork system. Where the working environment is not compatible with the selected levels of cleanliness, the specifier shall decide an alternative method of achieving the selected level, for example, by changing the level of protection, revising the ductwork installation programme or employing a

specialist cleaning contractor at commissioning stage. In the case of choosing the latter option, see Section 2.16 and, in particular, the benefits outlined in Section 2.16(iv).

2.12 It is the responsibility of the specifier to assess the acceptable risk of

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tender:

(i) the system and cleanliness quality class to be achieved (see

table 1)

(ii) the level of protection required for the ductwork as defined in

Sections 2.13 to 2.15.

(iii) the requirement for specialist cleaning (PDI Level 3) (where the

specialist cleaning contractor will be responsible for ensuring that the ductwork is cleaned to meet the post-clean verification test set out in Section 9 of this Guide).

The post clean integrity and maintenance of the system is outside the control of the cleaning contractor, it is therefore not appropriate to apply retention sums to cleaning works.

Protection, delivery and installation (‘PDI’)

2.13 Three levels of care and protection, PDI level 1, PDI level 2 and PDI

level 3, have been identified but, regardless of the specified choice, it is the responsibility of the main building contractor to provide the following:

(i) A dry and clean storage area adjacent to the working area for

ductwork and equipment and this may require a boarded floor and a water resistant covering.

(ii) A dry and clean working area.

2.14

PDI level 1 protection

Condition of ducts ex-works

2.14.1 Ductwork leaving the premises of the manufacturer will include some

or all of the following:

(a) Internal and/or external self-adhesive labels or marking for

part(s) identification

(b) Exposed mastic sealant

(c) Light zinc oxide coating on the metal surface (d) A light coating of oil on machine formed ductwork

(e) Minor protrusions into the airway from rivets, screws, bolts and

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(f) Internal insulation and associated fixings

(g) Discoloration marks from plasma cutting process (h) Scuff marks and small indentations.

It should be noted that ductwork will not be wiped down or specially cleaned at this level unless specified.

Delivery to site

2.14.2 Unless otherwise specified, ductwork delivered from the premises of

the manufacturer will have no protection. However, care must be taken to prevent damage during transportation and off loading.

Installation

2.14.3 Before the installation of individual duct sections, they are to be

inspected and should be free from debris. The ductwork will not be wiped down or specially cleaned.

Protection of ductwork risers

2.14.4 All risers must be covered to prevent the entry of debris into the

duct. In respect of the safety of personnel full regard should be given to the requirements of the Health and Safety at Work, etc., Act 1974.

Downward facing and horizontal duct openings

2.14.5 Downward facing and horizontal openings will not be covered.

Access provisions for on-going maintenance

2.14.6 The specifier shall define the size, location and type of access opening

required for maintenance, inspection and cleaning of the system (see Tables 1, 2, 3 and 4).

Access openings to in-duct plant

2.14.7 Access covers shall be firmly fitted in position on completion of each

section of the work.

PDI level 2 protection

2.15 In addition to the provisions of PDI Level 1, the following

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Site storage away from the working area

2.15.1 The area provided for storage shall be permanently clean, dry and

dust free and this may require a boarded floor and water resistant covering.

Installation

2.15.2 The working area must be clean and dry and protected from the

elements.

2.15.3 The internal surfaces of the ductwork shall be wiped prior to

installation. However, this would not be to a verifiable standard. For specialist cleaning see PDI Level 3.

2.15.4 Open ends on completed ductwork and overnight work-in-progress

shall be sealed except where solvent based sealants and cleaning materials have been used where capping off should only take place after an appropriate curing period has elapsed (see important consideration with regard to hazardous conditions, Section 2.18.2).

Second fix installation

2.15.5 In order to protect duct systems against dust ingress during

construction phase, dampers are to be left in the closed position by the ductwork contractor, to be opened by others at the

commissioning stage. It is prudent to post a warning notice to this effect at fan controls to avoid inadvertent operation and possible damage to fans and ductwork.

PDI level 3 (Pre-commission specialist cleaning)

2.16 In addition to PDI level 1, all internal identified labels must be

removed by the ductwork contractor either in the factory or on site. External labels are permissible.

Protection of ductwork on a construction site will not guarantee internal cleanliness of the ductwork. Where specific verifiable levels of internal cleanliness are required it will be the responsibility of the designer to specify the inclusion of a specialist cleaning contractor at the outset of a contract to internally clean newly installed ductwork just prior to commissioning work commencing (see Section 2.11). This approach would realise the following benefits:

(i) The actual number of cleaning access panels may be

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(ii) As a result of the involvement of a specialist cleaning

contractor, clear direction may be provided to the ductwork contractor as to the size and location of cleaning access panels required to be installed.

(iii) A specialist cleaning operation prior to commissioning would

enable the cleaning contractor to verify the practical access requirements for the future cleaning operations associated with regular maintenance programme.

(iv) A specialist cleaning operation prior to commissioning would

allow the specifier to reduce the need for wipe downs and capping-off - as referred to in clause 2.10, 2.15 and 2.18.1.

(v) The cleanliness of the installation can be confirmed and

documented by means of the post clean verification test procedure as set out in section 9.4 of this Guide and the issue of a report.

Summary

2.17 Table 3 is a summary of the Protection, delivery and installation

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Table 3 Protection, delivery and installation levels

PDI Level 1 PDI Level 2 PDI Level 3

Factory seal No No No*

Protection during transit No No No*

Protection during site

storage No See 2.15.1 No

*

Site pre-installation wipe

down No Yes No

*

Cap off on site Risers only

see 2.14.4

Yes Risers only see 2.14.4

Pre-commission specialist

cleaning Yes

† _Yes† _Yes

Other important considerations

Factory/Site sealing of ductwork 2.18

2.18.1 In certain circumstances such as clean rooms, operating theatres or

other high specification areas the specifier may require that the

internal surfaces of new ductwork are protected during transportation and site storage. This can be achieved by factory sealing all

ductwork either by blanking or capping duct ends, bagging small fittings, surface wrapping or shrink wrapping (see important

consideration with regard to hazardous conditions, clause 2.18.2). The specifier must clearly specify this requirement to the ductwork contractor and also to the Main Contractor in terms of ensuring dry/clean storage and working areas.

Hazardous conditions

2.18.2 In certain concentrations some cleaning materials and sealants can

pose a risk to operatives. The Control of Substances Hazardous to Health Regulations (‘COSHH’) require employers to assess the risk to employees’ health from using hazardous materials and take

precautions to minimise that risk. For example, when using internally applied solvent based sealants and adhesives on site, ducts should only be capped-off after an appropriate curing period has elapsed (normally a minimum of 24 hours). Ducts should be left to naturally ventilate prior to sealing-off the installed ductwork.

*_{Specifier may wish to request additional protection requirements referred to such as additional sealing} of open ends for delivery (see 2.18.1) or to ensure compliance with the protection requirements within BS15780

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Site drilling of ductwork

2.18.3 Swarf will be generated during the installation and possibly during

commissioning/air balancing, eg test probe covers. Some swarf will therefore remain inside the ductwork unless a form of on-going specialist cleaning is specified.

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3 Design and access to the internal surfaces of the

ventilation system

3.1 In accordance with BS EN 12236 2002 determination of load must be

considered for the additional weight of a person or persons who may gain access to ductwork for the purpose of cleaning or maintenance.

3.2 B&ES specification DW/144 covers the provision of access panels for

the inspection/servicing of adjacent items of in-line equipment. In a new ductwork system these are the only access panels that a

ductwork contractor will provide unless there is a clear indication by the designer/specifier as to their requirements for access to facilitate cleaning survey/inspection or cleaning activity (see Table 4 of this Guide).

3.3 This section gives general guidance regarding provisions for the

system hygiene inspection/testing and system cleaning of both new and existing ductwork systems. The location of access panels for these purposes is set out in Table 4. A specifier may consider

variances to this advice having taken due regard of specific cleaning methods.

3.4 The precise location, size and type of access would depend upon the

system design and the type of ductwork cleaning, inspection and testing methods to be adopted. The advice of the specialist cleaning contractor should be sought at an early stage.

3.5 DW/144 states that the required access panels for inspection/

servicing access to in-line equipment / components only should be installed by the ductwork contractor and that additional panels for cleaning should be installed as and when required by the specialist cleaning company. The specialist cleaning contractor, in addition to taking advantage of openings fitted by the ductwork installer, shall fit any additional cleaning openings themselves not only in order to suit their specific methods of cleaning but also to suit the practical site conditions relative to the fabric of the building and position of other services.

3.6 All openings shall be made safe and have sealed panels/covers

designed so that they can be speedily removed and re-fixed, ie multiple set screws and self-tapping screws are not acceptable as a method of fixing panels/covers to an access opening/frame.

3.7 It is essential to note that the tabulated access schemes cannot

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by the designer to the particular building, services and architectural interfaces and system requirements. The designer’s responsibility under the CDM regulations is to ensure that the system is designed so that it can be safety maintained, inspected and cleaned in

accordance with BS EN 12236 2002. The designer is therefore advised to seek guidance from a specialist cleaning contractor to ensure that system cleaning of any new design is practicable.

3.8 It is for the designer and the other project parties responsible for the

implementation of the design, under CDM “cascade” principles, to ensure that access panels are not obstructed by pipework cable trays or any other obstacle during the building process. Consideration should be given to the future use of the building including occupation.

3.9 Access panels in accordance with DW/144 should be suitable for the

purpose for which they are intended. They should incorporate quick release catches, sealing gasket and thermal, acoustic and fire-rated insulation properties equal to that of the duct to which the panel is fitted. The panel and aperture should be free of any sharp edges.

3.10 For system hygiene inspection and testing and for system cleaning,

Tables 5 and 6 indicate the minimum sizes of access panel required.

3.11 Generally it is acceptable to access a branch duct for cleaning by

removal of the flexible duct that connects to the grille plenums.

3.12 For the purpose of cleaning the ventilation system and its component

part, the recommended location of the access panels, size and type is aligned with British and European standard BS EN 12097.

3.13 This document reproduces this information in part, so as to establish

the location, size and type of access panels, for new build and upgrade of existing ductwork systems. These details are given in Tables 4, 5 and 6.

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Table 4 Guidance as to location of access panels for cleaning and inspection

One side Both sides

Control Dampers Yes

Fire Dampers Yes

Heating/Cooling Coils Yes

Attenuators (Rectangular) Yes

Attenuators (Circular) Yes

Filter Sections Yes

Air Turning Vanes Yes

Changes of Direction Yes

In Duct Fans/Devices Yes

Inlet/Exhaust Louvre Yes

Notes to Table 4

1 With regard to new ductwork installations DW/144 table 20 specifies the location of and responsibility for the installation of access doors.

2 Other than in the locations shown in Table 4, intermediate access panels should be located as a minimum every 15 m in horizontal ductwork systems for the purpose of normal usage but not greater than 1m from the throat of a square 90

bend.

3 For access requirements for kitchen extract systems see Section 7.

4 In the case of vertical ductwork, an access opening at the bottom and top of each riser and at each accessible floor should be provided for cleaning and inspection purposes.

5 Access panels can be positioned to allow access to more than one component depending on ductwork dimensions, distance between components and the cleaning technique used.

6 Access panels should normally be positioned as close as practicably possible to the item to be cleaned (0.5 m maximum).

7 A change of direction is deemed to be a 90 bend and branches. With regard to circular ductwork it is not necessary for there to be an access panel on every change of direction.

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Table 5 Recommended size of openings (rectangular & flat oval)

Duct size up to longest

side major axis Recommended dimension of openings

200 mm 300 mm 150 mm

300 mm 300 mm 200 mm

400 mm 450 mm 300 mm

≥500 mm 450 mm 450 mm

Table 6 Recommended size of openings (circular)

Duct size up to Recommended dimensions of openings

310 mm 250 mm 150 mm

450 mm 400 mm 300 mm

550 mm 400 mm 300 mm

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4 Specific considerations for system components

Air handling units & other system components

4.1 To obtain satisfactory conditions of cleanliness, all the components

associated with the ventilation system should be included in specific cleaning and maintenance procedures.

4.2 Inlets should be protected by weather louvres backed by maximum

12 mm mesh (vermin guard) and situated away from potential

sources of contamination. Heavy contamination within inlets prior to filters is common and may include insects, feathers, bird droppings, nesting materials, wind-blown leaves, grass, soil and paper. Inlets near roads may suffer carbon based deposits. Badly sited inlets are susceptible to heavy contamination and blockage by airborne

particulates and debris. They also act as a first stage, very course filtration (‘trash screen’). Regular cleaning is recommended.

4.3 Water entry as droplets or condensation can support mould growth in

inlets and make dirt deposits difficult to remove, as well as causing louvres, vermin guards and inlet ductwork to corrode and eventually disintegrate.

4.4 The provision of extra access panels may be required to give operator

entry to remove deposits by scraping, vacuuming, brushing or wet methods and to repair louvres, mesh and corrosion damage.

4.5 Where significant bird contamination or mould problems are

encountered, a preliminary disinfection before starting work may be required and appropriate protection provided for cleaning operatives. Due to the ingress of external and re-circulated deposits and

moisture within air inlets and pre-filter inlet ductwork it is a prudent measure to increase the frequency of inspection and cleaning of these sections to prevent conditions worsening and to stop the system fabric degrading.

Access to air handling units

4.6 Access to all sections of the air handling units is required for

adequate cleaning. Occasionally there is no usable access door to the space between sections, for example heating and cooling coils. In this event extra access panels may have to be installed subject to the design of the unit. Defective door and filter seals are a common and significant source of inward dirt leakage and filter bypass.

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Filters

4.7 Defective or incorrectly fitted filters, or inappropriate filter selection

and sizing may present an avoidable dust burden within ductwork systems. If left unattended, significant particulate contamination of the unit and ductwork may occur. Regular inspections of the filter sections are important to ensure they are not damaged, collapsed or blocked and are correctly seated and sealed against air bypass. A regular filter exchange programme should be conducted to maintain system performance and hygienic conditions.

Linings

4.8 Air handling units, ductwork and other system components may be

lined with Machine-Made Mineral Fibre (‘MMMF’) which may or may not be protected by a coating, foil or fabric. Damaged linings

releasing particles into the air system are common. Foam may be also be used as a lining. This can break down with age to release fine particles. Where damage is observed it must be reported so that it can be made good.

4.9 Many linings are porous and have the capacity to absorb dirt. They

require thorough but careful vacuum cleaning with a soft brush head to remove dirt without causing damage. Complete dirt removal is unlikely to be achieved.

4.10 Where moisture is present significant microbiological growth within

the lining is possible.

4.11 The existing condition of the lining, or potential damage caused by

cleaning activities, may necessitate the removal, repair or relining of the ductwork lining interior. Consideration should be given to

replacement with sealed lining to prevent ingress of moisture.

Moisture

4.12 Humidification and condensation on chilled surfaces and leakage can

cause dampness or in extreme cases standing water resulting in corrosion or excessive microbial growth. Similar problems can occur at droplet eliminators. Poor drainage of condensate from chilled coil drip trays may require cleaning of drain lines and traps. Treatments to prevent microbiological growth contaminating and blocking trays and drain lines are a possible option.

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proliferation of Legionella species are dealt with in ACOP L8 and NHS Guidance (see Appendix B).

Heating, cooling coils and heat exchanger coils

4.14 Coils with very closely spaced fins and/or which are very deep, can

suffer blockage due to accumulated dirt, corrosion and hardness deposits. They are prone to severe deterioration of the fins. Coils located before filters are particularly vulnerable. Heavily

contaminated heat exchangers will operate at low thermal efficiency leading to inefficient plant operation and increased running costs. Corrosion of heat exchanger fins and mounting frames, together with microbiological fouling and condensate carry over from the chiller batteries can create a source of contamination downstream of the primary filters. If the coil is in a duct, lack of access for inspection and routine cleaning can result in these being blocked with dirt, restricting air flow through them (methods as used for air handling units apply). Additional access panels to give access to both sides of the coil will usually be required.

4.15 Vacuum brushing, compressed air jetting, water washing, and the

application of chemical cleaning methods, singly or in combination may be required. Care must be taken to avoid damage to fins.

Heat recovery coils, thermal wheels, cross-over coils

4.16 Stringent building regulations and the need to control and reduce

energy costs has led to an increase in the use of heat recovery technology. Cross-over coils and thermal wheels are an efficient method of recovering heat from extracted air and transferring it to the incoming air via fins or plate heat exchangers.

4.17 Ductwork extraction and recirculation systems will naturally carry

varying levels of airborne contaminants, therefore these in-line and intricate heat recovery systems are open to dirt fouling and

subsequent reduction in heat exchange performance. Regular inspection and an appropriate programme of decontamination are advised.

Fans

4.18 Fans, motors and drives may be heavily contaminated especially if oil

or grease has leaked. Impellers may have heavy deposits on the blades. For full in-situ cleaning, partial dismantling and, possibly, the

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creation of extra access panels in fan casings, subject to

manufacturer approval, may be required. Fans can vary in size greatly. The types typically found within ventilation plant are axial flow, centrifugal or bifurcated. It is essential to ensure fans are electrically isolated and locked off before carrying out inspection or cleaning works.

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Sound attenuators

4.19 Sound attenuators (also called ‘silencers’) may be located within air

handling plant or situated remotely in ducts. These usually have linings covered with woven fabric or perforated sheet metal. Dirt readily accumulates in silencers and their porous nature makes complete cleaning impossible. Careful vacuum brushing with a soft brush head or very gentle application of compressed air are possible cleaning methods.

4.20 Where damage has occurred which may allow the release of MMMFs,

consideration should be given to repair or replacement.

Turning vanes, volume control dampers

4.21 These tend to accumulate dirt which can affect their operation and

will require access panels on both sides to allow full cleaning and surface restoration.

4.22 Volume control dampers can either be manually set or automatically

controlled. They are designed to regulate (balance) the airflow (volume) throughout the various branches of the distribution

ductwork. Found on all sizes of duct, both supply and extract, they can also be circular plate or iris type design on small round ductwork. These in-line components can become heavily fouled, especially in re-circulation or extract systems. Manually set volume control dampers should have the ‘as found’ setting marked indelibly to aid resetting.

Fire dampers

4.23 Fire dampers should be inspected annually as a minimum for correct

function and condition in line with the Regulatory Reform Fire Safety Order 2005 and physically cleaned when required. Inspection and functional testing of smoke/fire dampers should be separately specified.

Ductwork

Steel ductwork

4.24 The most common form of ventilation distribution material is

galvanised steel sheet. It can be constructed in a range of sizes and profiles, most common are rectangular and circular, however flat oval is also in use. These systems are typically of a rigid construction and are often hidden from normal view above false ceilings etc. Access is

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typically gained via installation of access doors either during installation or at the time of necessary cleaning works. On larger ductwork total man access may be necessary (see 3.1 and 10.5)

Flat or oval ductwork

4.25 Due to the flattened design this ducting contains many steel support

rods to provide strength and stability. Consideration must be given to installing sufficient access doors and the method of cleaning due to restricted access.

Phenolic ductwork

4.26 This is a light weight pre-insulated, rigid ductwork system made from

a phenolic compound and lined inside and out with a foil finish. It is a weaker structure compared to galvanised steel and care should be taken when cleaning not to damage the surfaces or over load with weight. Careful consideration should be given to access points to ensure the thermal quality and air tightness is maintained. Man access into this type of ductwork should not be undertaken.

Glass-fibre reinforced plastic(‘GRP’)

4.27 These ductwork systems are generally used where the contents of

the ductwork contain harmful or corrosive chemicals. They are typically associated with local exhaust ventilation (‘LEV’) systems. They are well sealed and most commonly associated with extraction only. Doors are typically prefabricated and sealed with specialist gaskets or mastic and bolted shut to ensure air tightness.

Air socks

4.28 These can be permeable textile or plastic-coated ducts which are held

in-situ by a series of runners and zips or Velcro fastenings. They can only be used for supply air as they rely on positive air pressure to inflate and offer good even air distribution. Air Socks require regular cleaning and have a relatively limited lifespan compared to steel ductwork.

Chilled beams

4.29 Passive, Active or Multi-service Chilled Beams are relatively low

maintenance devices but do require occasional cleaning due to dust collection from both tempered supply air and re-circulated air from the occupied space.

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Fire cladding and fire-rated ductwork

4.30 Access doors fitted must be of the same construction and must not

compromise the fire protection integrity of the system. Safety Notice - some older fibrous boarded products may contain asbestos. Always treat with caution and, if suspected as possibly containing asbestos, then consult a specialist before disturbing.

Flexible ducts

4.31 Flexible ducts trap dirt in the corrugations. This dirt can be difficult

to completely remove if the corrugations are deep and/or compressed together. Light weight foil, plastic flexible or aged flexible are liable to damage. Cleaning methods must be adjusted to account for the type of flexible duct. Brush methods require soft bristle brushes and gentle application. Compressed air methods may require a pressure reduction to avoid tearing the duct material.

4.32 It may be necessary to remove and extend flexible ducts to release

dirt from folds.

4.33 Decay of the material of construction, or difficulties in releasing

flexible ducts from their connection spigots without causing damage may make replacement a better option than cleaning.

Diffusers and grilles

4.34 Where possible these should be removed for cleaning. Washing to

remove grease and staining may be required.

4.35 Diffuser/grille locations and orientation should be marked or recorded

if they are to be taken away for washing, so that they can be returned to the correct location. Opposed blade dampers should have the ‘as found’ setting marked to aid resetting.

4.36 Certain grille and diffuser arrangements may be installed such that

they cannot be practicably removed for cleaning, eg linear diffusers or those trapped by partition walls. In-situ cleaning by air line and extraction to capture dislodged deposits may be used.

4.37 Diffusers may have plenum boxes, possibly containing dampers

behind them, which also require cleaning. Access will be required to permit cleaning or air jetting and extraction methods.

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Terminal equipment

4.38 Equipment such as fan coils, mixing boxes, air socks, VRV, CAV, VAV,

induction units and unit air conditioners may be included in a cleaning programme.

4.39 Wall and sill mounted equipment is frequently obstructed by difficult

to move furniture and fittings, preventing or hindering access for cleaning. Responsibility for moving obstructions should be defined by the specifier.

4.40 Ceiling mounted equipment may be obstructed by services and

structures preventing the opening of access panels and withdrawal of internal components. Some terminal units have filters which may require cleaning or which are disposable. Contractual responsibility for supplying replacement filters will require definition by the

specifier.

4.41 Terminal units may be lined or include attenuator sections.

Maintenance activity, ageing and erosion by air flow may have resulted in damage to the lining allowing fibre escape. If damage to the lining occurs remedial action should be taken immediately. The lining may have accumulated dirt within its matrix. The limited access to all air passages, especially labyrinth passages in

attenuators within terminal units and the presence of delicate porous linings can prevent total dirt removal.

4.42 Gentle vacuum brushing or air jetting, plus high volume extraction

may be required. Some units have air jet nozzles or small air

passages which become blocked with dirt. This dirt can form a hard deposit which requires mechanical removal with suitable tools to chip or ream it away. Jet nozzles may also require washing.

4.43 It is important for the specifier to define the extent of cleaning for

Induction Units, eg whether secondary and mixed air surfaces only are included or whether typically less accessible primary air surfaces (plenum box) are also included.

Plenum void

4.44 Ceiling and floor void plenums may be used as an integral part of the

air distribution system and should therefore, be subject to the same hygiene consideration as other system components. Regard should be given to the selection of cleaning technique(s) in view of the different construction materials used. In particular if MMMF is in place, careful consideration should be given to either cleaning or

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replacing such insulation where loose fibres are present.

4.45 Plenums are often exposed brickwork, mortar and plastered surfaces.

Their rough texture accumulates and traps particulates and can quickly become fouled and stained. Sealing course brick surfaces with an approved non-solvent sealant would reduce degradation and crumbling of the surfaces and enable dry cleaning methods to be adopted to remove accumulated dusts. Alternatively brickwork could be rendered or clad to provide a smooth and easily cleanable surface.

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5 System risk assessment (inspection/monitoring/testing)

5.1 Ventilation systems by their very nature will accumulate

contamination the degree of which will be influenced by the quality of the incoming air, filtration, design, maintenance and usage. Over time varying types of contamination will accumulate to levels which may detrimentally influence the quality of the supplied air and hence may affect the health of building users. Contaminant levels can build to such an extent that they provide the added risk of fire

propagation.

Legislation - health and safety law

5.2 The Management of Health & Safety at Work Regulations 1999

imposes a duty on every employer to make a suitable and sufficient assessment of:

(a) the risks to the health and safety of his employees to which they

are exposed whilst they are at work, and

(b) the risks to the health and safety of persons not in his

employment arising out of or in connection with the conduct by him of his undertaking.

5.3 The Workplace (Health, Safety and Welfare) Regulation 5 imposes a

duty to clean mechanical ventilation systems “as appropriate”.

Regulation 6 states, “effective and suitable provision shall be made to ensure that every enclosed workplace is ventilated by a sufficient quantity of fresh or purified air”.

5.4 Each of these regulations is accompanied by an approved code of

practice (‘ACOP’) which gives guidance on how compliance with the regulations can be achieved.

5.4.1 ACOP 22(A) relating to Regulation 5 of the Workplace (Health,

Safety and Welfare) Regulations, states that regular maintenance (including, as necessary, inspection, testing, adjustment, lubrication and cleaning) should be carried out at suitable intervals.

5.4.2 ACOP 33 relating to regulation 6 of the Workplace (Health, Safety

and Welfare) Regulations, states that “mechanical ventilation systems (including air conditioning systems) should be regularly and properly cleaned, tested and maintained to ensure that they are kept clean and free from anything which may contaminate the air”.

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British Standard BS EN 15780 provides benchmarks to define

cleanliness and dirtiness.

Monitoring (inspection and testing) frequency recommendation

5.5 The ACOP noted in 5.4.1 makes specific reference for the need for

regular maintenance including inspection and testing at suitable intervals, BS EN 15780 details the frequencies.

The assessment frequencies described on Table 7 should be

considered as the minimum recommendations and the necessity of increasing them will depend on the environment conditions, on the activity and on mechanical and human conditions in both building and its surroundings.

In most cases inspection frequency should be specified rather than cleaning frequency as the amount of contaminant identified during inspection may alter the actual required cleaning frequency.

Please refer to section 7 for inspection and testing of kitchen grease extract systems.

Table 7 Recommended minimum regular inspection/monitoring intervals (in

months) according to system quality class (‘SQC’)

Inspection and Testing Intervals (months)

SQC AHU Filters(2) _{Wet areas}(1) _Ducts _Terminals

Low 24 12 6 48 48

Medium 12 12 6 24(3) ₂₄(3)

High 12 6 6 12(4) ₁₂(4)

Notes to Table 7

1 Wet areas of the ventilation systems comprise humidification, cooling coils, condensate trays and other ancillary or associated items of plant containing these elements.

2 Filters should be inspected and maintained according to the manufacturer’s recommendations, with these intervals as the minimum.

3 For compliance with HTM03, this frequency should be increased to 12-monthly. 4 For compliance with HTM03, this frequency should be increased to 3-monthly.

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Identification and assessment of risk

5.6 A suitable and sufficient risk assessment is required to identify and

assess the risk of contamination levels in a ventilation system. Such contamination may have accumulated to a degree which could be detrimental to both the building users and processes being

undertaken within the building. Precautionary measures to reduce risk should therefore be identified and remedial measures put into action. The person on whom the statutory duty falls is required where specialist testing is necessary to have access to competent help in conducting the assessment. They should ensure that whenever specialist advisors are used that the advisors have

sufficient understanding and expertise of the work activity they are undertaking.

5.7 The scope of a risk assessment should include, but not be restricted

to:

(a) provision of suitable access points, if not present.

(b) visual inspection. This may be assisted by the use of equipment

such as cameras, endoscopes and robotic CCTV with appropriate records such as photographs and video footage.

(c) quantitative duct surface dust measurement by an approved

method. Where grease or adhered deposits are clearly the issue then only the deposit thickness test (‘DTT’) method or the wet film thickness test method (‘WFTT’) detailed in section 7 and Appendix D, should be used. A minimum of three test points per system should be included a specific representative number of tests should be agreed prior to the risk assessment taking place. An average should be calculated across all tests

conducted on each system and used to determine whether it is appropriate to clean the system. However, individual results that are excessively high may indicate a need for local attention. Where it has been decided that microbiological colonisation of system surfaces could be a risk factor then suitable

microbiological sampling should be agreed as part of the risk assessment.

(d) The following components should be subject to cleanliness

inspection as a minimum:



Fresh air intakes, air handling unit including filters and coils and selected in-duct plant and ancillaries such as

attenuators, fire dampers, volume control dampers, heat exchangers, VAV boxes, etc.

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changes of direction, terminations, straight horizontal and vertical ducts.



A selection of terminal equipment such as flexible ducts, grilles, diffusers and equipment, eg induction and fan coil units.

The number of inspection locations and tests should be clearly defined by the specifier.

The client should be given the opportunity to witness the sample testing of ductwork surfaces.

(e) The inspection of maintenance records and air hygiene

management log book including:

i. record drawings

ii. filter inspection and replacement regimes

iii. previous condition monitoring records

iv. fire damper operational test records, and

v. previous cleaning or remedial work records.

The significant findings of the risk assessment should be

recorded (if there are five or more employees) and should detail recommendations for remedial actions and on-going monitoring programmes.

Testing procedures

5.8 Testing procedures are defined in this Guide that should be used to

establish whether or not it would be appropriate to clean a mechanical ventilation system. These provide reasonable and

practicable ways of satisfying the Regulations and ACOPs relevant to the cleanliness of ventilation systems as detailed above. Specific guidance on testing methods is given in Appendix D.

5.9 It should be noted that there is a clear difference between tests to

monitor ventilation system surface condition and tests to monitor ‘ventilation air quality’. This Guide is concerned with surface condition tests. These will indicate the potential for the system to release contaminants into the air at any point in the future and affect subsequent system performance/energy efficiency, whereas air

quality tests will indicate contaminants that are actually in the air, but only at the time of collecting the sample.

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5.10 Monitoring of system condition through regular testing will allow the

rate of accumulation to be ascertained and the appropriate action to be determined and budgeted for. In certain instances it may be considered necessary to set more frequent inspection intervals where specific risks have been identified in the event of particle release into the airstream (eg, operating theatre supply).

5.11 In order to establish an objective method for determining when a

ventilation system is considered dirty in terms of particulate and hence when it would be appropriate to clean, two alternative testing methods are recommended as follows, these can be used during risk assessment or routine monitoring. Both test methods provide an objective method of measuring internal duct floor surface deposits:

Deposit thickness test (‘DTT’)

5.11.1 Suitable for instant on site assessment for flat metal duct surfaces

during risk assessment where system quality classes have not been defined. The DTT method determines the mean surface deposit in terms of micron thickness. A result above the limits set out in table 8 would define a cleaning requirement.

Preferred vacuum test (‘PVT’)

5.11.2 This method requires on site sample collection and subsequent off

site laboratory analysis. It determines the mean deposit weight in grams per m2 and is suitable for circular, flat-oval and rectangular duct types. This method is recommended by BS EN 15780 and applies to three system quality classes.

NOTE: Separate testing and contaminant levels specifically for kitchen

extract systems are detailed in Section 7.

5.12 The PVT - a development of the vacuum test - forms part of the new

British and European Standard BS EN 15780 previously mentioned.

5.13 BS EN 15780 has a requirement to categorise each system type as

low, medium or high class depending on the areas being served. These levels of System Quality Class should be generally applied as follows:

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Table 1 Typical applications of system quality classes (from section 1, repeated below)

SQC Typical examples

Low Rooms with only intermittent occupancy, eg storage rooms

Medium Offices, hotels, restaurants, schools, theatres,

residential homes, shopping areas, exhibition buildings, sport buildings, general areas in hospitals, general working areas in industries

High Laboratories, treatment areas in hospitals, high quality offices

To comply with the system quality classification PVT samples should show results below the limit values given in Table 8.

5.14 The table below sets out what would be considered as acceptable

contamination levels in existing ‘in service’ ductwork. These contamination levels as detailed in Table 8 below should not be confused with:

(a) Post-clean level set for verification of cleanliness ‘following a

system clean’, this is far more stringent and these levels are detailed in section 9, or

(b) with cleanliness levels for ‘newly installed ductwork’, these

levels are detailed in Table 2.

Table 8 Acceptable contamination levels in existing ductwork

SQC

Acceptable

contamination level Supply ductwork

Acceptable contamination level Re-circulation or secondary air ductwork

Low <4.5 g/m2 _{<6.0 g/m}2

Medium <3.0 g/m2 _{<4.5 g/m}2

High <0.6 g/m2 _{<3.0 g/m}2

5.15 Unacceptable fouling levels of extract ducting is defined below, at

which point cleaning would be considered necessary. For dry dust-affected extract ductwork (where the air is discharged to

atmosphere) less stringent limit values are applied, in comparison with supply ductwork. Extract systems should be cleaned when airflow through the system reduces by 15% or more. If such measurement is not practicable, then the gravimetric dust level

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measurement may be used. An extract duct should be cleaned when the dust level exceeds 9.0 g/m2_{, using the preferred vacuum test}

method.

5.16 The results of any monitoring undertaking must be recorded in a

suitable consistent format, assessed by the responsible person and any necessary maintenance actions identified implemented. Records of all monitoring and maintenance tasks undertaken should be

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6 Cleaning Methods

6.1 This Guide is not intended to be prescriptive in relation to the method

of cleaning, as there are many existing and emerging technologies available depending upon the type of deposit to be removed. To conform to this Guide, the actual application of the methods listed in Table 9 must be capable of achieving the required result.

6.2 Ductwork cleaning should ideally be undertaken in the direction of the

air flow to prevent the risk of cross contamination between cleaning shifts. On buildings with multiple zones (ie, floors) these works can be planned to take advantage of the natural cut off points at the risers. Careful planning at the pre-contract stage is essential in ensuring a successful cleaning regime.

Considerations when using dry cleaning methods

6.3 In all cases where mechanical cleaning techniques are used, the

particulate should be collected using an air movement and

containment machine (negative air pressure extraction techniques). This will generally require appropriate filtration and should assist in the containment of contaminants.

Considerations when using wet cleaning methods

6.4 Moisture can assist in the growth of micro-organisms and the system

should be thoroughly dried prior to commissioning/re-commissioning. The introduction of cleaning chemicals or biocides should only be

considered where a risk assessment has been carried out, the details recorded and any adverse effects of the applied chemicals have been assessed and determined with appropriate safe procedures set out in a formal method statement.

Steam cleaning and high pressure water wash are not recommended for ductwork that is situated above ceilings or in sensitive areas unless carried out in a controlled manner to contain leakage. Again, procedures must take account of operative safety and should be set out in written form.

Careful consideration should be given to the use of chemicals and/or water for surfaces that are porous, eg internally lined ductwork, attenuators, fibre board ductwork etc, as permanent damage may result.

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Before applying wet cleaning methods care should be taken to ensure that condensed vapours and cleaning fluids can be removed from the ductwork system.

Mechanical brushing

6.5 This method of ductwork cleaning typically applies to ducts not

exceeding 600 diameter or 500  500 as above this size the effectiveness can be limited.

The basic principles of this method are based around the

agitation/disturbance of the duct surface deposits in conjunction with negative pressure high volume extraction to remove and collect the deposits.

Compressed air whip/skipper ball

6.6 Much like rotary brushing, this method of cleaning is best applied on

ducts typically not exceeding 600 diameter or 500 x 500.

This uses a compressed air source and compressed air line with a specially designed nozzle on the end which blasts the ductwork with compressed air thus removing the deposits. This method of duct cleaning is normally best employed when the deposits within a duct are only loosely adhered to the surfaces.

Again, this system is used in conjunction with a negative pressure high volume extraction unit to remove and collect the deposits.

Air lance

6.7 This method of cleaning utilises a compressed air line with a gun and

trigger attached to one end that can be used to dislodge localised deposits.

It is best utilised when cleaning difficult to access, intricate areas or delicate areas which may become damaged by more aggressive cleaning techniques.

It is important to consider the collection of the deposits when using this method as there is a risk of not being able to collect all of the deposits which have been dislodged and this could result in cross contamination. Normally it would be best to use the air lance to blow the deposits into a contained location where they can then be

TR19

GUIDE TO GOOD PRACTICE

Internal cleanliness of ventilation systems (TR19)

Acknowledgement

Publishing history:

Foreword

Table of Contents

1

Introduction

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2

Protection, delivery and installation standards for

maintaining the internal cleanliness of new ductwork

prior to commissioning and/or handover

Introduction

Air movement devices and in line plant and equipment

Notes for designers and specifiers

Protection, delivery and installation (‘PDI’)

PDI level 1 protection

PDI level 2 protection

PDI level 3 (Pre-commission specialist cleaning)

Summary

Other important considerations

3

Design and access to the internal surfaces of the

ventilation system

4

Specific considerations for system components

Air handling units & other system components

Access to air handling units

Filters

Linings

Moisture

Heating, cooling coils and heat exchanger coils

Heat recovery coils, thermal wheels, cross-over coils

Fans

Sound attenuators

Turning vanes, volume control dampers

Fire dampers

Ductwork

Diffusers and grilles

Terminal equipment

Plenum void

5

System risk assessment (inspection/monitoring/testing)

Legislation - health and safety law

Monitoring (inspection and testing) frequency recommendation

Identification and assessment of risk





Testing procedures

6

Cleaning Methods

Considerations when using dry cleaning methods

Considerations when using wet cleaning methods

Mechanical brushing

Compressed air whip/skipper ball

Air lance