AS 1668 2 supp 1 1991 the use of mechanical ventilation and

STANDARDS AUSTRALIAAustralian Standard The use of mechanical ventilation and air-conditioning in buildings Part 2: Mechanical ventilation for acceptable indoor-air quality—Commentary Sup

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AS 1668.2 Supp 1-1991 The use of mechanical ventilation and air-conditioning in

buildings - Mechanical ventilation for acceptable indoor-air quality - Commentary

(Supplement to AS 1668.2-1991)

Licensed to LUU MINH LUAN on 25 Feb 2002

Conditioning It was approved on behalf of the Council of Standards Australia on

20 May 1991 and published on 1 July 1991

The following interests are reprsented on Committee ME/62:

Association of Consulting Engineers, AustraliaAustralian Assembly of Fire AuthoritiesDepartment of Administrative ServicesAustralian Construction ServicesAustralian Institute of Environment HealthAustralian Institute of Refrigeration Air Conditioning and HeatingAustralian Uniform Building Regulations Coordinating CouncilBuilding Owners and Managers Association of AustraliaCouncil of Air Conditioning and Mechanical Contractors Associations of AustraliaCouncil of the City of Sydney

Confederation of Australian IndustryFire Protection Industry Associations of AustraliaInsurance Council of Australia

Metal Trades Industry Association of AustraliaPublic Works Department, N.S.W

Review of Australian Standards To keep abreast of progress in industry, Australian Standards are subject to

periodic review and are kept up to date by the issue of amendments or new editions as necessary It is important therefore that Standards users ensure that they are in possession of the latest edition, and any amendments thereto Full details of all Australian Standards and related publications will be found in the Standards Australia Catalogue

of Publications; this information is supplemented each month by the magazine ‘The Australian Standard’, which subscribing members receive, and which gives details of new publications, new editions and amendments, and of withdrawn Standards.

Suggestions for improvements to Australian Standards, addressed to the head office of Standards Australia, are welcomed Notification of any inaccuracy or ambiguity found in an Australian Standard should be made without delay in order that the matter may be investigated and appropriate action taken.

First published as SAA MP47.C2–1980.

Revised and redesignated AS 1668.2 Supp1–1991.

This Commentary on AS 1668, The use of mechanical ventilation and air–conditioning in buildings, Part 2: Mechanical ventilation for acceptable indoor–air quality, was prepared by

the Standards Australia Committee on Mechanical Ventilation and Air Conditioning toprovide guidance on the application of the Code by explaining the intent of those clauseswhich could be the subject of requests for interpretation

T h i s p u b l i c a t i o n s u p e r s e d e s S A A M P 4 7 , P a r t C 2 : C o m m e n t a r y o n A S 1 6 6 8 , SAA Mechanical Ventilation and Airconditioning Code, Part C2: Ventilation requirements.

The contents have been revised to incorporate all alterations included in AS 1668,Part 2–1991

The clause references in the Commentary are those for the corresponding clauses in AS 1668,Part 2–1991, prefixed by the letter ‘C’

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C1.1 SCOPE 4

C1.2 APPLICATION 4

SECTION C2 SUPPLY AIR DILUTION PROCEDURE C2.1 SCOPE OF SECTION 5

C2.2 OUTDOOR AIR INTAKES 5

C2.3 OUTDOOR AIR FLOW RATES 5

C2.5 OUTDOOR AIR MIXING AND DISTRIBUTION 6

C2.6 OUTDOOR AIR FLOW 7

SECTION C3 EXHAUST DILUTION PROCEDURES C3.1 SCOPE OF SECTION 8

C3.2 GENERAL EXHAUST VENTILATION 8

C3.3 LOCAL EXHAUST 8

C3.4 AIR FROM ENCLOSURES HAVING EXHAUST AIR REQUIREMENTS 8

C3.5 REPLENISHMENT OF EXHAUST AIR 9

C3.6 COMBINATION OF EXHAUST SYSTEMS 9

C3.7 AIR DISCHARGES 9

SECTION C4 VENTILATION OF ENCLOSURES USED BY VEHICLES WITH INTERNAL COMBUSTION ENGINES C4.2 APPLICATION OF SECTION 10

C4.3 GENERAL CASE 10

C4.4 CARPARKS 10

C4.5 ENCLOSURES OTHER THAN CARPARKS 11

C4.6 QUEUING AREA 11

C4.8 REPLENISHMENT OF EXHAUST AIR 11

C4.10 STAFF—VENTILATION RATE 11

C4.11 LOCATION OF EXHAUSTS IN BELOW GROUND ENCLOSURES 11

C4.13 MONITORING OF ATMOSPHERIC CONTAMINANTS 12

APPENDICES CA DERIVATION OF THE AIR CLEANING EFFICIENCY EQUATIONS USED IN APPENDIX D, AS 1668 PART 2 13

CB BASIS OF AIR FLOW RATES FORMULAE FOR CARPARKS 25

CC DERIVATION OF AIR FLOW RATES FOR QUEUING AREAS 27

STANDARDS AUSTRALIA

Australian Standard The use of mechanical ventilation and air-conditioning in buildings

Part 2: Mechanical ventilation for acceptable indoor-air quality—Commentary

(Supplement 1 to AS 1668.2–1991)

SECTION C1 SCOPE AND GENERAL

C1.1 SCOPE Present building regulations (and the Australian Model Uniform Building Code) are based on the

assumption that natural ventilation will be the first ‘natural’ choice and arbitrary minimum criteria for such

‘natural’ ventilation are prescribed Presumably the occupants will have control over this aspect of theirenvironment in the type of space where natural ventilation is employed

In the event of the criteria not being met, e.g percentage of floor area as openable windows or fixed openingsand/or distance from openings are insufficient, then mechanical ventilation or air-conditioning would be required,

as a permissible substitute Where the criteria were met, then mechanical ventilation or air-conditioning would

be a permissible substitute at the constructor’s option – generally at a higher cost

AS 1668, Parts 1 and 2 are references in both State and Territory building regulations and in the recently

published Building Code of Australia Where mechanical ventilation is required by such regulations and codes,

compliance with AS 1668 is prescribed This therefore places constraints on the wording of the Standard thatwould not otherwise be necessary

AS 1668.2–1980 provided some interpretations of the application of natural ventilation to carparks as prescribed

in building regulations Since AS 1668.2 is only referenced in building regulations in respect to mechanicalventilation requirements, consideration was given to the deletion of these natural ventilation interpretations TheAustralian Uniform Building Regulations Interstate Committee deemed it appropriate that such interpretationsremain in AS 1668.2 at this time They have therefore been developed in more detail in the revision for furtherclarification The wording of the Standard in respect of the use of natural ventilation has also been changed toprovide a more logical basis for its inclusion

Although AS 1668.2 has been incorporated in State and Territory building regulations, its use has beensupplemented or replaced in specific areas by local codes The revision is expected to achieve greater acceptance

of AS 1668.2 except where a local code also addresses air-conditioning Although the title of AS 1668.2 has beenchanged from ‘Ventilation requirements’ to ‘Mechanical ventilation for acceptable indoor-air quality’ theextension of the Standard to include comfort in terms of the control of temperature, humidity, air-movement ornoise was still deemed to be inappropriate at this time These elements are therefore only addressed in terms ofthe definement of limits beyond which health or safety may be impaired

C1.2 APPLICATION The applications of the Standard are now more precisely described by direct reference

to the specific application of each section

To provide greater assistance in the use of the Standard, a logic diagram has also been included

SECTION C2 SUPPLY AIR DILUTION PROCEDURE

‘out-door air’ used in place of ‘outside air’

This has been done to remove possible misunderstandings and to achieve conformity with American Society ofHeating, Refrigeration and Air-conditioning Engineers (ASHRAE) and other overseas Standards

C2.2 OUTDOOR AIR INTAKES

C2.2.1 Location The work of Wilson, Halitsky and others indicates the complicated wake effects and the

interaction between adjacent obstructions and the intakes and discharges of a building

Chapter 14 of the 1989 ASHRAE Fundamentals Handbook contains a comprehensive coverage of air flow around

buildings, dispersion of building exhaust gases and design to minimize re-entry

Particularly critical cases may warrant wind tunnel testing of models

C2.3 OUTDOOR AIR FLOW RATES

C2.3.2 Occupancy In some cases, the occupancies used for the purposes of determination of outdoor air flow

rates may differ in aggregate for a given floor from those used for egress provisions in the Building Code of Australia.

This can arise as a result of the use of the maximum occupancy for each area with no account taken of movement

of people from one area to another at different times during the period of occupancy An example would be aconference room used substantially by the occupants of adjacent areas on the same floor

Table A1 and the associated notes comprising Appendix A need to be read together

maintain acceptable air quality depend on the definition of ‘acceptability’ The rates specified in the Standardare consensus values, and have been arrived at after extensive consideration of published research, rates used inthe past, changing patterns of occupant behaviour, and changing patterns of pollution emissions within thebuilding

The Standard requires outdoor air flow rates in accordance with Appendix A, but allows reductions if a sufficientquantity of recycle air is treated to remove contaminants at an efficiency that meets the requirements of theappropriate formula from Appendix D It should be noted that:

(a) The total supply air quantity (i.e recycle air + outdoor air) must exceed the air quantity required by Appendix

A, otherwise the formula will require an efficiency greater than 100%

(b) The efficiency for removal of particulate contaminants must be as determined using one of the specified testprocedures

(c) No test procedure for determining efficiency of removal of odours and gaseous contaminants is nominated

as there is no recognized procedure It will be necessary for designers proposing such air treatment to justifythe method used to determine the efficiency

If air treatment is provided that removes particulates, tobacco smoke odours, and body odours, the Standardrequires a minimum air flow rate for dilution of other gaseous contaminants that are generated in buildings such

as CO2, ozone, formaldehyde and volatile organic hydrocarbons

If air treatment is provided that removes only particulates, the Standard requires a minimum air flow rate for

dilution of gaseous contaminants and odours, a0, that is based on the air quantity necessary to dilute body odours

In enclosures where heavy smoking occurs, such as bars, this will not control odours from tobacco smoking, butthis is considered acceptable on the basis that occupants have a choice of whether they enter and remain for anextended period in these enclosures

For control of body odours, recent studies by Bouwan, Cain, Fanger and others show an outdoor air flow rate of7.5 to 10 L/s/person to be appropriate and to be a consensus value of minimum ventilation rates in the US,Germany and the UK The Standard requires a rate of 7.5 L/s/person, increasing to 15 L/s/person for enclosures

in which temperatures are not kept below 27°C by air-conditioning or other means, as the generation and/or theperception of body odours increase with temperature

It was additionally recognized that children are more odorous than adults; the tabulated ventilation rates for someoccupancies reflect this

For special enclosures, such as operating theatres, a high value of a0is specified, so that no reduction in outdoorair flow rates is allowed if recycle air treatment is provided

If no air treatment is provided, the Standard requires the minimum outdoor air flow rates to be in accordance withAppendix A The rates in Appendix A take account of contaminants from smoking Based on the work of Wanner,Weber and Johansson, concentration of carbon monoxide may be taken as an indicator of the concentration ofcontaminants from tobacco smoke A limit of 1 p.p.m of CO from tobacco smoke is considered necessary tomaintain acceptable indoor air quality.

The rates listed in Appendix A, other than those for special enclosures, can be divided into those applying toareas subject to moderate, medium or heavy smoking, for which the rates are 10, 15 and 20 L/s/personrespectively

For an enclosure in which an excess of environmental tobacco smoke load is anticipated, it is recommended thatoutdoor air quantities should be increased to an appropriate value Where occupants are required by theiremployers to enter and remain for an extended period in such enclosures, it is recommended that ventilationsystems should be designed so that the employees receive an appropriately higher amount of outdoor air.Building ‘leakage’ or a requirement for make-up air may result in a need for higher levels of outdoor air flowthan the prescribed minimum

unused ‘outdoor air’ with ‘return air’ is well developed in Appendix D of the Standard Derivation of the aircleaning efficiency equations used in that appendix are included as Appendix CA to this commentary

For single enclosures the formulae in Appendix D used to determine the required efficiencies are straightforward(Clauses D2.2.1 and D.2.2.2) For a group of enclosures for which a multiple enclosure factor is applicable, theappropriate formula depends on the location of the air treatment in the system, and the formula can becomplicated Clause D2.3 of Appendix D provides formulae for some configurations, for which the derivationsare set out in Clause CA2.3 of this Commentary For any other configuration proposed, the appropriate formulawould have to be derived by the designer

C2.3.7 Variable air volume systems Clauses 2.3.6 and 2.3.7 are both designed to take account of variations

in air flows in variable air volume systems

Table A1 in Appendix A of the Standard specifies the minimum outdoor air flow rates that must be supplied to

one enclosure to maintain an indoor air quality that, in the present state of knowledge, should eliminate possible

adverse effects of the indoor air on healthy adult occupants remaining in this enclosure for unrestricted periods.Quite often one air-handling plant supplies air to more than one such enclosure The question then arises: Howmuch outdoor air has to be introduced to the air-handling plant so that the minimum air quality required by thisStandard will be maintained in all enclosures served by this air-handling plant?

The formula given in Clause 2.3.6(a) provides the answer to this question and is known as the Multiple Enclosure

Formula, and yields the Multiple Enclosure Factor ‘M’ The derivation of this formula can be found in Appendix

D of the Standard and a nomogram is provided (Figure 2.2 of the Standard) to simplify the computation of M The factor M is usually greater than one The reason for this is obvious from the derivation and Example D1 in

Appendix D

One way of satisfying the requirements of this Standard, would be to introduce into the air-handling plant,sufficient outdoor air, so that the outdoor air content in the air supplied by the air-handling plant, would bedetermined by the use of the highest ratio of outdoor air to total supply air for any enclosure, applied to the total

of air supplied to all enclosures This would certainly satisfy the Standard but would not be economical since allenclosures with lower ratios would be oversupplied with outdoor air

The Multiple Enclosure Formula is based on the fact that the air returned from enclosures oversupplied withoutdoor air still has some potential to dilute pollutants to satisfactory levels when introduced into the supply ductfrom the air-handling plant to enclosures

It should be evident that further economies can be achieved by the grouping of enclosures with like ratios ofoutdoor air to total air on the same air-handling plant This of course may not be possible or appropriate in manycases for a variety of reasons

C2.5 OUTDOOR AIR MIXING AND DISTRIBUTION The purpose of this Clause is to ensure that all

enclosures supplied with air by an air-handling plant receive at all times the minimum amount of outdoor airrequired by the Standard

As it is not practicable to measure the outdoor air content and its distribution in the air supply duct, therequirements of this Clause will be satisfied if the system design provides for –

(a) minimum outdoor air to be carried at all times by the supply ducts from the air-handling plant to allenclosures; and

(b) sufficient mixing of outdoor air with the recycle air in the air-handling plant to supply all enclosures withair of about the same ratio of outdoor to recycle air

A well designed mixing chamber before the main fan in a single supply duct system would satisfy this Clause.

It would also satisfy the clause for other systems if the design provides for the minimum outdoor air to bedelivered to each enclosure under all possible conditions of operation, i.e from full heating to full cooling TheStandard accepts that this condition will be met if all supply ducts carry the same fraction of outdoor air.The other requirement of this Clause of the Standard that outdoor air be well distributed within the occupied zone

of an enclosure is to ensure the elimination of pockets of stagnant air where pollutants could accumulate

C2.6 OUTDOOR AIR FLOW

It is well recognized that additional body odour is generated at elevated temperatures The determination ofoutdoor air flow rates in Table A1 of Appendix A of the Standard for the ‘no smoking’ requirement is usuallybased on odour control Recognize that, in the majority of applications, air-conditioning would be used.Where this is not the case, or for some other reason, temperatures in excess of 27°C occur under normaloperation, rates must be adjusted upwards to compensate for increase in body odour generation by occupants

C2.6.2 Systems serving enclosures with transient or variable occupancy The intent of this Clause is to

conserve energy use in terms of the hours of operation of mechanical ventilation systems related to periods ofoccupancy of the enclosures served

This provision was introduced by ASHRAE into its Standard on Ventilation For Acceptable Indoor Air Quality

in 1979 and is included in ASHRAE 62–1989

The rationale provided in the ASHRAE Standard is included as Appendix J in AS 1668.2–1991

It should be recognized that although a system may be turned off during periods of non-occupancy a period ofpost-purging will be required after departure of occupants to clear pollutants generated by the occupants Also

a period of pre-purging may be required before entry of occupants to clear accumulation of pollutants generated

by furnishings and other materials, etc., within the space

SECTION C3 EXHAUST DILUTION PROCEDURES

C3.1 SCOPE OF SECTION The supply air dilution procedure prescribed in Section 2 of the Standard is adequate

in most circumstances to control the level of contaminants in the indoor air

Where enclosures contain processes which generate contaminants of a type or concentration deemed in the Standard to

be objectionable or dangerous, it is required that these be removed directly from the enclosure by a separate exhaustsystem and not be recirculated through the supply air system

It is also required that the exhaust air flow rate be adequate to dilute the contaminants and be arranged to discharge themoutside the building in such a manner that no harm or offence results to people outside the building

Section 3 of the Standard defines enclosure and effluent types requiring exhaust and prescribes minimum exhaust airflow rates and methods of exhaust

Enclosures used by vehicles with internal combustion engines are dealt with in a separate section Refer to Section 4

of the Standard

C3.2 GENERAL EXHAUST VENTILATION This refers to the removal of effluents which are generally spread

throughout the enclosure by the ‘dilution principle’ The concern here is to keep the concentration of effluent down to

or for sanitary compartments where excess odours are generated

In kitchens, local exhaust must be used in addition to the specified general exhaust, where the size of cooking apparatusexceeds the limits stated in Clause 3.3.1(b) of the Standard

The requirement for the general exhaust rate to exceed the supply rate (where used) by 10 percent is simply to ensurethat effluent cannot flow to adjacent enclosures

Where mechanical ventilation is used to produce pressure differentials between different enclosures, the requirement forthe general exhaust to exceed the supply may be waived if a general exhaust system is not required by the Standard,

or where a required general exhaust can be replaced by a local exhaust system to approval

Air locks may not need to be separately ventilated, and reference should be made to the Note under Table 3.2 in theStandard for the relevant requirements

C3.3 LOCAL EXHAUST

C3.3.1 Types of effluents requiring local exhaust In the current Standard, the types of effluents have now been

grouped into two categories instead of the five categories used in the previous Standard This is intended to simplify theapplication of the Standard and is based on experience gained since this Standard was first published

Type A effluents which are dangerous are required to have the point of generation enclosed and this enclosure exhausted.Type B effluents are more of a nuisance than a danger and the most common application would relate to kitchen exhausthoods

C3.3.2 Effluent removal Apart from establishing requirements for local exhaust, the Standard does not attempt to

prescribe the form, capture velocities or air flow rates of hoods or other means used for local exhaust of effluents.One exception to this in the previous Standard was kitchen hoods for which the Standard provided design guidance,owing to a perceived absence of authoritative publications Although this situation has been improved to a large extentand some States have industry standards covering this subject, the Committee believed that the best interests of all partieswho use this Standard nationally would be served by the continued inclusion of design guidelines on kitchen hoods.Having made this decision, work was done on revising and expanding this material to improve its usefulness This nowcomprises Appendix E of the Standard An additional Appendix F has been included to provide some design guidelinesbut these do not constitute part of the Standard in terms of building regulations

For other applications, references are included in the Standard to other Australian Standards and to the IndustrialVentilation Manual published and regularly revised by the American Conference of Governmental Industrial Hygienists.Australian Standards now exist for the design of laboratories and should be referred to in regard to local exhaust andmake-up air provisions in such applications

C3.4 AIR FROM ENCLOSURES HAVING EXHAUST AIR REQUIREMENTS The intent of this Clause is to

require the regulatory authority to allow return air to be recycled from enclosures in which local exhaust air collection

is used, provided that there is no reason against doing so Approval, of course, would be conditional upon evidence thatthe design of the local exhaust will prevent effluent being carried into the enclosure from which air was to be recycled.Clause 3.4.3 essentially re-states the requirements of Clause 3.2.3 of the Standard

C3.5 REPLENISHMENT OF EXHAUST AIR It is often overlooked in design that the performance of a

mechanical ventilation system is dependent on achieving a balanced flow of supply and exhaust air

This Clause in the Standard makes provision for the make-up supply air for a mechanical exhaust system, whethergeneral or local, to be naturally or mechanically provided

Conditions under which either would be approved are provided The quality of the make-up air may not be socritical where there is only short-term occupancy involved An example is given of make-up air from a carparkbeing acceptable for a garbage room exhaust system Another example would be exhaust air from a kitchen beingreplenished from an adjacent eating area or office but not from an adjacent toilet

Make-up air from an enclosure served by a non-required exhaust system in conjunction with a mechanical supply

or natural ventilation system should be considered Also make-up air from an enclosure ventilated by a requiredexhaust system may in some cases be acceptable, as indicated in the above examples

In some applications, air change rates are likely to be high in an enclosure due to local exhaust air flowrequirements Where this could result in severe discomfort and the risk of such systems being turned off byoccupants, heating or cooling of the make-up air may be desirable

Clause 3.5.4 of the Standard is intended to cover the situation where a local exhaust is used intermittently butrequires a mechanical supply air system for make-up In such circumstances, control of the systems would benormally located adjacent to the local exhaust and not integrated into the total building or floor mechanicalventilation system

C3.6 COMBINATION OF EXHAUST SYSTEMS The Committee gave consideration to the reduction of

groups in Table 3.2 of the Standard but concluded that there was no identifiable benefit and possible increasedsystem costs that would result from such a change

It should be understood that duct connections between enclosures in different groupings present a problem whenthe exhaust system is not in operation rather than when in use

It may also be unacceptable to combine the process exhausts or exhausts from laboratory fume hoods duringsystem operation Such applications are not included in this Standard because they are, or will be, covered byother Australian Standards, e.g Australian Standard relating to laboratory planning

C3.7 AIR DISCHARGES Although the objective of this Standard is achievement of acceptable indoor air

quality, the implication of this in terms of any impact on the surrounding environment of air discharges from thebuilding is directly related to this objective It was therefore necessary to prescribe requirements to control suchair discharges

As in the previous Standard, this Clause attempts to cover most situations that are likely to occur and again, asnot all combinations of circumstances can be foreshadowed, guidelines have been laid down to provide forunusual or novel situations The inference is still maintained that some exhaust discharges may be found to beobjectionable to the extent that treatment may be required before final discharge into the environment

The minimum separation distance of 6 m given in Clauses 3.7.2(b), 3.7.2(e) and 3.7.3(c) of the Standard

is intended to convey an awareness of the significant distances necessary to prevent cross-contamination It was

not determined by any rigorous computation and reference to ASHRAE Handbook–1989 Fundamentals , Page

14.12 will provide further guidance

SECTION C4 VENTILATION OF ENCLOSURESUSED BY VEHICLES WITH INTERNAL

COMBUSTION ENGINES

C4.2 APPLICATION OF SECTION Ventilation of enclosures used by vehicles with internal combustion

engines has now been established as a separate section from other exhaust ventilation requirements

Generally, there has been an expansion of applications but vehicular tunnels have been deleted since these arenot directly related to buildings and are more adequately covered in such internationally recognized documents

as prepared by the Permanent International Association of Road Congresses (PIARC) Technical Committee onRoad Tunnels

Provision is now made to use a mechanical supply air system as an alternative to a mechanical exhaust air systemwhere natural means of make-up (or air relief) are deemed acceptable

As stated in C1.1 Scope, the treatment of natural ventilation provisions has been revised and expanded to improveinterpretation

C4.3 GENERAL CASE Two categories of occupants must be taken into account in such enclosures; these are

the occupants of vehicles using the enclosure and those who work in the enclosure Standards of exposure aredifferent for each category and the difference is mainly related to the period of exposure and frequency ofexposure

C4.4 CARPARKS

ventilation to full natural ventilation The conditions under which concessions may be made to omit one or bothmechanical ventilation systems are listed sequentially to assist in the determination of requirements for aproposal

Areas of carparks where natural ventilation may be used are now also clearly defined together with conditionsunder which natural ventilation of such areas may be approved The use of diagrams to assist in clarification hasalso been expanded

Unfortunately, the Committee was unable to locate any substantial research on systematic assessment ofperformance with respect to natural ventilation In many cases, regulatory authorities continue to require designparameters on the basis that the observance of such parameters has not resulted in any complaints from users ofsuch carparks

There are significant differences between the natural ventilation parameters established by regulatory authorities

in each State and Territory The Committee was unable to achieve agreement between even two of the States and,where unavoidable, adopted a compromise in this revision of the Standard It is hoped that funds will be madeavailable for research in terms of levels of carbon monoxide found in naturally ventilated carparks so thatparameters adopted in the next revision of this Standard can be more soundly based

It should however be clearly understood that Clause 4.3 of the Standard places responsibility on owners to ensurethat concentrations of atmospheric contaminants within the carpark do not exceed exposure standards listed byWorksafe Australia

A breeze blowing across a carpark having opposite sides reasonably open will generally be more effective inremoving car exhaust fumes than a mechanical ventilation system The unpredictability of wind strength andfrequency must be recognized and will limit the effectiveness of natural ventilation provisions under still airconditions

C4.4.2 Air flow rates The formulae in the previous Standard which utilized a ‘simultaneous operation factor

C’ to allow reductions in air flow rates for multiple level carparks has been replaced with formulae that can be

used for all carpark applications

Experience with the use of the formulae in the previous Standard revealed shortcomings which included theapplication to carparks with large areas but few levels Problems in application also arose where exits and entrieswere on different levels or in several locations on one level

The formulae in the new Standard utilize a ‘parking usage factor’ which takes account of the different usagepatterns of carparks associated with various building projects, e.g shopping centre and office building carparks.The basis of the air flow rates formulae are provided in Appendix CB of this Commentary This also containsthe basis of the ‘parking usage factors’ in Table 4.1 of the Standard

C4.4.2.2 Small carparks For small carparks with 50 or less car spaces, simplified formulae have been included

in this Clause of the Standard

C4.4.2.3 Number of car spaces The figure of one twenty-third (1/23) of floor area has been arrived at through

surveys conducted of existing carparks It is a density that can be reached in certain circumstances The mostsatisfactory approach is to show car spaces on the drawings of the proposed carpark

C4.4.3.2 Location of openings The previous Standard stated that the objective of the location of exhaust

registers is ‘to ensure thorough scavenging of effluents from the enclosure and to be as far as possible from thesource of make-up or supply air’ Owing to difficulties in the evaluation of interpretations of this principle, therevised Standard translates the objective into specific requirements which can be more consistently assessed

To assist in the interpretation of these more specific requirements, example carpark layouts complying with thisClause are included in Appendix L of the Standard

C4.5 ENCLOSURES OTHER THAN CARPARKS The revised Standard groups in this Clause all other

enclosures used by vehicles with internal combustion engines

Changes in scope are confined to the exclusion of vehicular tunnels (not fully covered by the previous Standard),and the inclusion of dynamometer engine testing facilities to automotive service and repair shops and the addition

of areas used by special purpose vehicles

The Clause relating to drive-in facilities in the previous Standard was deemed to address more accurately vehiclequeuing areas Since these areas can also be considered part of a carpark, they have been dealt with in a separateClause 4.6 in the revised Standard

C4.5.1 Enclosed driveways associated with buildings This Clause replaces Clause 3.13.3.3 of AS 1668.2–1980 C4.5.2 Loading docks The adjustment to values in Clause 4.5.2 of the revised Standard from the values in the

previous Standard, reflects those derived in Appendix CB of this Commentary for carpark air flow rate formulae

Standard was that used to determine air flow rates for carparks The revised Standard uses a direct methodconsidered to be more appropriate

C4.5.4 Vehicular lifts and shaft

C4.5.4.1 Exhaust ventilation of vehicular lifts The minimum exhaust air flow rate of 3000 L/s is based on an

assumption that only one vehicle engine is operating at any time This is also the basis of the ventilation rate forthe lift shaft

the American Conference of Governmental Industrial Hygienists, Industrial Ventilation – A Manual of Recommended Practice.

C4.6 QUEUING AREA The rationale for information contained in Tables 4.4 and 4.5 of the Standard is

provided in Appendix K of the Standard

C4.6.3 Air flow rate and distribution of air The derivation of the exhaust air flow rates in this Clause is

contained in Appendix CC to this Commentary

C4.8 REPLENISHMENT OF EXHAUST AIR Generally, the intent is that ventilation of enclosures used by

vehicles with internal combustion engines ensures that the contaminants produced by engine operation arecontained within that enclosure and exhausted therefrom to outdoors The use of a mechanical supply ventilationsystem should not lead to pressurization of the carpark resulting in contaminated air spilling over into adjacentenclosures subject to human occupation

C4.10 STAFF–VENTILATION RATE As stated in C4.3, exposure standards are different for short and long

term occupants of enclosures used by vehicles with internal combustion engines

Where staff are roving continually through the enclosure, e.g carpark attendant, it may be impractical to provide

an environment which would meet the exposure standard In many applications even roving staff spend asubstantial part of their shift at a base station Special attention should be given to the provision of an acceptableair quality at that base station

Fixed areas occupied by staff within an enclosure should, where possible, be themselves substantially enclosedand pressurized by a supply air ventilation system

The required outdoor air flow rates have been maintained at the same levels as in the previous Standard

C4.11 LOCATION OF EXHAUSTS IN BELOW GROUND ENCLOSURES Distribution of exhaust air

intakes between low level and high level locations is dictated by the density of motor vehicle exhaust emissionsand emissions of hydrocarbons arising from leakage from vehicle fuel tanks and lines The latter, being heavierthan air, falls to and flows along the floor and ultimately accumulates at the lowest point, under still airconditions

Uncontrolled accumulations of hydrocarbons can result in an explosion A likely ignition source is a spark from

a vehicle starter motor It is therefore critical to induce air movement at floor level of basement enclosures so

as to minimize the risk of hydrocarbons accumulating to explosive concentrations This is most important duringtimes when vehicles are present but there are no vehicle movements to assist in stirring the air

High level exhaust is still a requirement to ensure that lighter than air components (including smoke from a fire)are effectively removed

C4.13 MONITORING OF ATMOSPHERIC CONTAMINANTS The intermittent generation of atmospheric

contaminants in enclosures used by vehicles with internal combustion engines results in the required mechanicalventilation systems operating for periods when an acceptable air quality can be maintained without such dilutionventilation

Regulatory authorities have recognized submissions by building owners in this regard and have allowed operation

of ventilation systems to be regulated by automatic controls using carbon monoxide monitors

The Committee considered the development and use of such monitoring control systems to be now well advancedand reliable A section has therefore now been included in the Standard and is based on the requirements for COmonitoring contained in the Sydney City Council’s Ventilation Code

Suppliers of two monitoring systems were invited to attend a meeting of the Committee and to submit proposalsfor this section for consideration

Final drafting was undertaken by selected members of the Committee and the content modified to suit themonitoring of other atmospheric contaminants as well as CO