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Technical Guidance on Hygiene

HVCA GUIDE TO GOOD PRACTICE CLEANLINESS OF VENTILATION SYSTEMS - TR/19 SECOND EDITION (A SUMMARY)

Swiftclean Directors were extensively involved in the original production of this Guide in terms of drafting text, editing, proposing the deposit thickness test and field trail of the same. They were also involved with the amendment/updating of TR/19 to its current format second edition 2002.

We believe that it is an excellent document to assist in compliance with the Workplace (Health, Safety & Welfare) Regulations 1992 and the management of Health & Safety at Work Regulations 1999 where pertinent to Ventilation System Cleanliness.

The guide, which can be purchased from Swiftclean or direct from the HVCA, gives detailed advice on the following:-

DESIGN AND ACCESS TO THE INTERNAL SURFACES OF THE VENTILATION SYSTEM:

  • Access door specifications are clearly defined for inspection purposes and also for cleaning purposes.
  • It should be noted that using certain techniques it is possible to clean systems using less access doors than that detailed in the Guide, but consideration should always be given to both verification of cleaning and access requirements for alternative future cleaning, inspection and testing.
  • A specifier would be advised to ensure clarity of the access door requirement in terms of position, size, type and quantity.

SPECIFIC CONSIDERATIONS FOR SYSTEM COMPONENTS:-

  • Typical problems are highlighted against the various components and materials found within a system which could have an adverse effect on the hygiene of a ventilation system.
  • A designer should take note of these and try to design out the potential problems.
  • A Specifier should ensure that all points are covered within a ventilation system cleaning specification and that a contingency is put aside for anything that is unquantified at tender stage.

SYSTEM TESTING (INSPECTION/MONITORING)

  • A testing procedure is defined, which can be used to establish when it is ‘appropriate’ to clean a ventilation system, in terms of particulate contamination.
  • The testing methods recommended are to measure the accumulation of deposits on the internal base surface of a ventilation system, to indicate the potential for the system to release contaminants into the air at some point in the future.
  • Two alternative testing methods are recommended; they are:- (1) Deposit Thickness Test (DTT), which determines the mean thickness of deposits in terms of micron measurement (+/-3 microns) and (2) Vacuum Test (VT) which determines the mean weight of deposits in term of grams per metre square. Both test methods are objective. The down side of the vacuum test is that it is not repeatable at an identical location and there is normally a waiting period for laboratory results of 2 or 3 days.
  • Tests are recommended to be repeated at intervals not exceeding 12 months. It would be prudent to carry out testing more frequently in more sensitive areas, (i.e food preparation, high occupancy).
  • Guideline surface deposit limits are set at: 180 microns (DTT) or 6g/metre square (VT) for extract systems 60 microns (DTT) or 1g/metre square (VT) for supply/recirculation systems.
  • In certain instances it may be considered necessary to set more stringent deposit limits, for example operating theatre or pharmaceutical production supply systems.

CLEANING METHODS

  • The guide does not recommend any one cleaning technique over another, it simply defines the various methods of removing deposits.
  • Considerations are also highlighted to consider when using dry or wet methods.

SPECIFIC CONSIDERATIONS OF KITCHEN EXTRACT SYSTEMS

  • •Risk factors are defined due to accumulation of condensed grease and cooking oils on systems surfaces. A significant risk of fire, odour, hygiene and vermin problems can develop.
  • Access door requirements are defined specifically for cleaning grease laden ductwork.
  • Annual cleaning of kitchen grease extracts is recommended as a minimum.
  • TR/19 was updated to strengthen, in particular, advice for kitchen extract systems. It includes a measurement method (the wet film thickness test) and grease thickness limits where cleaning is considered appropriate.

HAZARDOUS CONTAMINATION

  • Advice is offered on dealing with potentially hazardous deposits.

VERIFICATION OF CLEANLINESS

  • The guide states that the primary method for verifying the effectiveness of a cleaning operation should be visual.
  • An objective verification test is also defined using the vacuum test (VT) method. The achievement of 0.075g/metre square or less following cleaning would be considered acceptable. Any new installation should ideally meet this standard prior to handover.

HEALTH & SAFETY

  • Advice is offered on dealing with the health risks associated with a ventilation system cleaning contract.

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TM26:2000 - A SUMMARY

This summary has been provided to give an overview of the guidance content in TM26. It is recommended that a full copy of the document be purchased from CIBSE Publications Department (ISBN 1903287111)

FOREWORD

Swiftclean were represented on the TM26 Steering Group and also assisted with the pre publication field testing of the protocols.

INTRODUCTION

Produced in October 2000 by the Chartered Institute of Building Services Engineers (CIBSE) TM26 aims to demonstrate to Building Managers the importance of ductwork maintenance and to provide practical guidance on the proper procedures for the maintenance of ductwork systems in a safe and effective state.

LEGISLATION

Building Services are expected by legislation to provide a comfortable and safe indoor environment for occupants. Relevant legislation includes:-

  • The Health and Safety at Work Act 1974
  • The Management of Health & Safety at Work Regulations 1999
  • The Workplace (Health, Safety & Welfare) Regulations 1992
  • The Control of Substances Hazardous to Health Regulations

The legislation is being interpreted as addressing the quality of air provided in terms of taking steps to prevent its contamination by ‘potentially’ harmful gases and dust.

THE STATUS OF TM26

  • TM26 provides professional guidance. It sets out a procedure for addressing the microbiological cleanliness of ductwork systems, which when included with HVCA TR/17 procedures to ensure (visible dust) cleanliness is intended to represent good practice in the maintenance of the microbiological hygiene.
  • To assist in executing a duty of care to building occupants acceptable benchmarks targets for microbiological activity are defined in TM26 which can be used by building managers in an inspection programme to decide when cleaning is necessary on microbiological grounds. TR/17 (HVCA) defines benchmark targets for acceptable particulate levels and these can be used to decide when cleaning is necessary on the grounds of particulate matter (dust) accumulation.

DUCTWORK HYGIENE INDICATORS

  • Two approaches can be taken when assessing suspected microbiological problems, these are (A) Qualitative and (B) Quantitative.

The qualitative approach involves the sampling, culturing (growing) and identifying specific micro-organisms known to be associated with particular health problems. This approach would be impractical for routine monitoring.

The quantitative approach involves sampling, culturing and counting the total number of microbial cells or spores present, normally referred to as the total viable count (TVC). The purpose of TM26 is to give a system of sampling which provides an indication of the hygiene of ductwork under normal operating conditions, it was therefore considered appropriate to set guidelines based on TVC - the quantitative approach.

  • The culturing procedure requires two different growth mediums, one to culture bacteria and one to culture fungi. It is important that those mediums specified in TM26 are used, otherwise the acceptable benchmark targets can not necessarily be used.
  • Procedures are defined for sampling firstly the air in occupied spaces and secondly the internal surfaces of ventilation systems

AIR QUALITY IN BUILDINGS

  • Settled deposits in ductwork may cause contamination of supply air by means of the release of chemicals such as odorous VOC’s produced either microbiologically or chemically
  • Heavily microbiologically contaminated deposits may release microbes into the air stream.
  • Many indoor pollutants can be harmful to human health, either through their potential to cause infection, their toxic nature, or their potential to cause allergic reactions in susceptible individuals
  • Many microbes can survive for long periods in dry conditions, but they require moisture to grow. The combination of free water on the bottom of ducts, or elevated in duct relative humidity, together with dust to provide nutrient can provide the ideal conditions for microbial growth

The main requirements for microbial growth are:-

  • A source of food (dust)
  • Oxygen
  • Temperature, ideally between 15oC and 25oC
  • Moisture

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For more information on Legionella risk assessment please contact us: legionella@swiftclean.co.uk or free phone 0800 243 471.

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