CODE OF PRACTICE FOR THE CONTROL OF LEGIONELLA BACTERIA IN COOLING TOWERS
CONTENTS
FOREWORD 1
ACKNOWLEDGEMENTS 2
PART I: PRELIMINARY
1. Purpose 3
2. Scope and application 3
3. Responsibility 3
PART II: COOLING TOWERS IN BUILDINGS
4. Cooling tower design and construction 5
5. Location of cooling tower 6
6. Source of water 6
7. Discharge of water 6
8. Commissioning and operation 7
PART III: SERVICING, MAINTENANCE AND
MONITORING OF COOLING SYSTEM
9. Maintenance 8
10. Cleaning and disinfection 9
11. Water treatment 10
12. Biocide 11
13. Record keeping 12
14. Action plan for an outbreak 13
15. Water sampling and bacteriological monitoring 15
16. Enforcement action for legionella and standard plate count contamination 16
PART IV: WORKER SAFETY
17. Training 19
18. Personal Protection of workers 19
Appendices
A. Information required for the registration of cooling 21
towers
B. Allowable limits for trade effluent discharge to a 22
public sewer
C. Checklist for assessment of health risk of cooling 23
towers
D. A record of responsibility and activities to control 25
legionella bacteria in a specified cooling system
E. References 26
F. Glossary of terms 28
1
FOREWORD
Legionnaires’ disease is an acute bacterial infection of the lower respiratory
tract. Among the elderly and persons whose body resistance is weakened by other
concurrent illnesses, the infection can be fatal. The disease is caused by the inhalation
of tiny water droplets containing the legionella bacteria which thrive in poorly
maintained cooling towers. Proper maintenance of cooling towers with regular
mechanical cleaning, and routine treatment with biocides is therefore important and
necessary.
To minimise the risk of outbreaks of legionnaires’ disease in Singapore, the
Institute of Environmental Epidemiology, Ministry of the Environment, in consultation
with other government departments and professional bodies, formulated this Code of
Practice for the control of legionella bacteria in cooling towers. It is intended for
building owners/management corporations of centrally air-conditioned offices and
factories, contractors involved in the servicing and maintenance of cooling towers, and
others responsible for the design, operation and maintenance of air-conditioned
buildings.
This document specifies the design, construction and location of cooling
towers. It also provides guidelines on servicing and maintenance of cooling towers. It
includes a checklist for assessment of health risk of cooling towers and emergency
remedial measures in the event of an outbreak.
Building owners/management corporations are reminded that based on the
Environmental Public Health (Cooling Towers and Water Fountains) Regulations
2001, it is an offence to operate cooling towers that are grossly contaminated and pose
a health hazard.
WANG NAN CHEE
COMMISSIONER OF PUBLIC HEALTH
MINISTRY OF THE ENVIRONMENT
SINGAPORE
2
ACKNOWLEDGEMENTS
The advice, comments and contributions of the following departments and
professional bodies are gratefully acknowledged:
Quarantine & Epidemiology Department, Ministry of the Environment
Prosecution & Contracts Unit, Ministry of the Environment
Drainage Department, Ministry of the Environment
Environmental Health Department, Ministry of the Environment
Central Building Plan Unit, Ministry of the Environment
Sewerage Department, Ministry of the Environment
Pollution Control Department, Ministry of the Environment
Building Engineering Division, Building and Construction Authority
Department of Industrial Health, Ministry of Manpower
Medical Laboratory Board, Ministry of Health
Pathology Department, Singapore General Hospital
Singapore Association of ASHRAE Members
Singapore Institute of Architects
Institution of Engineers Singapore
Singapore Contractors Association
3
PART I
PRELIMINARY
1 Purpose
1.1 The purpose of this Code of Practice is to provide guidelines for the
prevention and control of legionella bacteria in cooling towers in order
to minimise the occurrence and risk of outbreaks of legionnaires’
disease.
2 Scope and application
2.1 This document applies to all cooling towers in new and existing
premises which are used as shops, offices, trade, business, industry or
for any other purposes in Singapore.
2.2 It is applicable for use at various stages during the inception, design,
upgrading, refurbishment, extension and maintenance of the building.
2.3 In this document, references to specific requirements under the relevant
legislations are made. Failure to comply with these requirements shall
constitute an offence under the respective regulations, and appropriate
enforcement action shall be taken.
3 Responsibility
3.1 It shall be the responsibility of the owner/management corporation of
the premises with cooling towers to:
(a) assess the risk of occurrence of legionnaires’ disease arising from
cooling towers;
(b) set up and manage a programme to minimise the risk of an
outbreak of legionnaires’ disease and monitor the effectiveness of
the programme;
(c) keep records of all activities implemented; and
(d) ensure the safety of operation and maintenance personnel and that
they are adequately trained.
4
3.2 The owner/management corporation shall ensure that persons
designated to carry out the responsibilities specified above are
competent, adequately qualified and experienced. Where the
owner/management corporation lacks the expertise, it shall be delegated
or contracted to consultants with the relevant experience and expertise.
3.3 The owner/management corporation shall ensure that every water
cooling system in the premises is registered with the Ministry of the
Environment, using the form in Appendix A.
3.4 The owner/management corporation shall ensure that there is an
instruction manual for every air-conditioning system incorporating:
(a) a schematic plan of the air-conditioning system;
(b) its operation;
(c) the necessary precautions to be taken specifying checks and their
frequency, and steps to be taken to remedy defects and deficiencies;
and
(d) equipment supplier’s particulars/contact numbers.
5
PART II
COOLING TOWERS OF BUILDINGS
4 Cooling tower design and construction
4.1 At the stage of the construction of the building and the installation of
cooling system, inspection shall be made by competent persons so that the
cooling towers pose minimal health risk to occupants of the building and
members of the public.
4.2 Cooling systems shall be designed and constructed so as to minimise the
release of drift and to aid safe operation, and regular cleaning and
disinfection.
4.3 The design of the cooling system:
(a) shall be simple and practical (deadlegs, loops and bends should be
avoided and redundant pipework removed); and
(b) shall allow for easy access to all parts of the system for inspection,
sampling, cleaning and disinfection.
4.4 A new or refitted cooling tower shall have features that minimise the
formation and release of drift, in particular:
(a) a water distribution system within the cooling tower designed to
create as little spray as possible;
(b) an effective high efficiency drift eliminator; and
(c) an enclosure of the area above the cooling tower pond. This will
reduce the effects of windage that cause the drift to escape through
the sides. It should not be transparent or translucent as sunlight can
promote the growth of algae which is conducive for the growth of
legionella bacteria.
4.5 Construction materials shall be non-corrosive, resistant to chemicals (e.g.
fibre glass, stainless steel), smooth, non-porous, opaque to sunlight and
readily disinfected. Materials used shall not support the growth and
proliferation of microorganisms.
6
4.6 A drain shall be located at the lowest point of the pond with a drain-down
valve so that the entire system can be conveniently and completely
drained.
5 Location of cooling tower
5.1 The cooling tower shall be located at least 5 metres away (measured from
the base of the cooling tower) from air circulating and ventilating inlets,
open windows and occupied areas, pedestrian thoroughfares, trafficable
areas, areas of public access, exhaust discharges from kitchens, air
handling system or other areas where nutrients conveyed from these
systems could assist in the growth of legionella.
5.2 When locating a cooling tower, the influence of adjacent buildings and of
prevailing wind direction and the wind distribution over these buildings
shall be taken into account. It shall be located away from the downwind of
air intakes for the building.
6 Source of water
6.1 The source of make-up water shall be supplied by the Public Utilities
Board water mains or any source as may be approved by the
Commissioner.
7 Discharge of water
7.1 Discharge of effluent water from cooling towers shall be into the public
sewers in accordance to the Sewerage and Drainage Act Cap. 293A.
Approval for connection to sewers shall be obtained from the Central
Building Plan Unit, Pollution Control Department, Ministry of the
Environment.
7.2 The concentration of chemicals in the effluent shall be within the allowable
limits of the Sewerage and Drainage (Trade Effluent) Regulations 1999
administered by the Pollution Control Department, Ministry of the
Environment (Appendix B).
7.3 Water from supply or condensation or other sources in the ventilation or
air-conditioning system shall be discharged into a pipe or drain
incorporating a U-bend and an air break between the condensate drain pipe
7
and the floor trap so that potentially contaminated water is prevented from
being drawn back into the ventilation or air-conditioning system.
8 Commissioning and operation
8.1 The specifications and operations of the air-conditioning system shall be in
accordance to all the provisions of the Singapore Standard Code of
Practice for Mechanical Ventilation and Air-Conditioning in Buildings (SS
CP13: 1999 or any revision thereafter).
8.2 Cooling towers shall be properly commissioned before use to ensure that
they operate correctly and safely.
8.3 The entire air-conditioning system shall be clear of any construction debris
and dirt, and cleaned before operation starts.
8.4 Precautions shall be taken to control the risks during commissioning, start
up and during the normal operation of the system.
8.5 In existing buildings:
(a) Where a cooling tower is out of use for more than five days, it shall
be drained, thoroughly cleaned and disinfected before re-use.
(b) Where a cooling tower is not in use, it shall be drained and kept dry.
8
PART III
SERVICING, MAINTENANCE AND
MONITORING OF COOLING SYSTEM
9 Maintenance
9.1 Cooling towers shall be maintained in a clean working condition and in a
good state of repair. A “good state of repair” would mean that there is no
defect in the operation, and the cooling towers should be free from
physical damage or deterioration which may arise from defects, such as,
rusty pipes.
9.2 Every system shall have a comprehensive maintenance manual that
incorporates:
(a) complete building plans of cooling and ventilation systems;
(b) cleaning methods, decontamination procedures and dismantling
instructions;
(c) procedures for water treatment; and
(d) shutdown and start-up procedures.
9.3 The regular maintenance of the cooling system shall be carried out by
competent persons, familiar with the prevention of any hazard arising from
the work.
9.4 Cooling towers shall be visually inspected at least once a week for any
physical defect, general cleanliness, organic fouling and presence of
physical debris.
9.5 A comprehensive maintenance programme including cleaning, disinfecting
and water treatment for every cooling tower shall be carried out to prevent
legionella bacteria from multiplying and to allow water treatment
chemicals to work more effectively.
9.6 Physical devices incorporating use of copper-silver ionisation, filtration,
ultraviolet light or ozone may be incorporated to complement maintenance,
but they shall not replace a proper and regular maintenance programme.
9
10 Cleaning and disinfection
10.1 Thorough cleaning, disinfection and manual desludging of cooling towers
shall be carried out at least once in six months.
10.2 Cleaning and disinfection shall also be carried out in cooling towers:
(a) that have been contaminated during construction, or by dusts or
organic matter;
(b) that have been shut down for more than five days;
(c) that have been mechanically altered or disrupted in a manner which
may lead to contamination;
(d) at regular intervals where the surrounding environment is dusty or
where the water quality is out of control; and
(e) where the adjacent cooling tower has been implicated as a source of
an outbreak of legionnaires' disease.
10.3 By-pass systems or alternating re-circulating pump systems where water is
stagnated shall be regularly cleaned and disinfected or brought into use.
10.4 The procedures for cleaning and disinfection shall be as follows:
(a) The system water shall be pre-chlorinated to achieve a measured
residual of 5 mg/litre free chlorine, to minimise health risk to
cleaning staff. Circulate water together with a biodispersant, to
enhance the effectiveness of chlorination, for 6 hours, maintaining a
minimum of 5 mg/litre free chlorine at all times. If the circuit pH
value is greater than 8, the measured residual will need to be in the
range of 15-20 mg/litre free chlorine in order to achieve the required
disinfection level. An alternative procedure to provide a more
effective use of chlorine is to introduce a heavy bleed-off for several
hours to reduce the pH of the system and its chlorine content;
(b) The circuit shall be drained and the tower, sump, and distribution
system manually cleaned. Accessible areas of the towers and its
pack shall be adequately washed. Scale and other deposits that have
not been removed shall be dissolved using chemical descalants,
carefully chosen to avoid damage to the circuit/cooling tower.
Cleaning methods which create excessive spray such as high
pressure water jetting shall be avoided. If this is not possible, the
cleaning shall be carried out when the building is unoccupied or in
the case of permanently occupied buildings, windows and air inlets
in the vicinity closed. Staff involved in water jetting shall be
10
adequately trained and wear suitable respiratory protective
equipment set out in section 18.2;
(c) The system shall be refilled with fresh water, and re-chlorinated to
maintain a minimum level of 5 mg/litre free chlorine throughout the
period of 6 hours. A biodispersant shall be used to enhance the
effectiveness of chlorination; and
(d) The system shall be drained and flushed, refilled with fresh water
and dosed with the appropriate start-up level of treatment chemicals,
including biocides.
During the procedure, the cooling tower fans should be switched off.
11 Water treatment
11.1 To control legionella bacteria, the water treatment regime shall prevent or
adequately reduce the amounts of:
(a) scale and corrosion products which might protect legionella bacteria
in the system;
(b) sediments which might prevent water treatment processes from
working effectively; and
(c) other bacteria and microorganisms.
11.2 A complete automatic water treatment shall be installed for accurate
dosing comprising:
(a) a metering pump; and
(b) a chemical dosage pot for feeding the chemicals.
11.3 Slime and algae growth shall be controlled with biocides. If there is a
sudden bloom of slime and algae, an alkaline cleaner to remove and
disperse the growth shall be applied, the system flushed, cleaned, and
biocide redosed.
11.4 The control of silt deposit shall be achieved by a chemical treatment
programme using dispersants or formulated chemicals.
11
11.5 The chemical used in the water treatment programme shall have no
detrimental effect on non-metallic materials such as rubber or epoxy anticorrosive
lining which may be used in the piping system. It shall be
compatible and neutral to the pipework materials.
11.6 No system shall be treated with any chemical or compound for which there
is no test procedure.
11.7 All packaging, storage and handling of chemicals shall be in accordance to
the manufacturer’s recommendation.
A checklist for assessment of health risk of cooling towers is shown in Appendix C.
12 Biocide
12.1 At least two (2) types of biocides shall be used alternately on a weekly
basis to prevent emergence of resistant strains of microorganisms.
12.2 Before setting up a biocidal water treatment programme, it shall be ensured
that the system is clean.
12.3 The ‘shot/slug dose’ method shall be implemented to prevent
microbiological acclimatisation. This involves the addition of the biocides,
alternating them at suitable intervals, directly into the cooling tower basin
using an automatic control system.
12.4 The biocide used to eliminate and control the growth of legionella bacteria
shall comply with the following:
(a) It shall not be a prohibited chemical in the Poisons Act Cap. 234 for
trade effluent discharge to a public sewer;
(b) It shall be effective against a wide range of micro-organisms
(including all legionella bacteria) at the recommended dilutions, and
its effectiveness supported by official independent reports;
(c) It shall be manufactured by the supplier to an independent
specification such as the British Standard 5750 or other approved
equivalent standards;
(d) It shall already have been in widespread use for similar field
application in the country of manufacture for no less than 3 years;
12
(e) It shall be proven to be effective when dosed in accordance to the
manufacturer’s recommendations (frequency, dose strength,
preparation);
(f) It shall have documentation available covering the safety and
effectiveness of the product in recirculating systems;
(g) It shall not interfere with the method used for identification of
legionella bacteria;
(h) It shall be chemically and physically compatible with processed
water and neutral to piping materials.
12.5 The chemicals used and the subsequent end-products of the treatment
programme shall be degradable with minimal hazards to the environment
in the event of accidental spillage or through draining into effluent
treatment plants, meeting all the necessary requirements of the Ministry of
the Environment under the Sewerage and Drainage (Trade Effluent)
Regulations 1999.
13 Record keeping
13.1 A formal record book for every cooling tower with accurate and adequate
information shall be kept and be made available for inspections by officials
from the Ministry of the Environment.
13.2 The record shall include:
(a) a description of the cooling tower such as location, model and
capacity;
(b) the name of the person who ensures that proper records are kept;
(c) the person or company who is responsible for the assessment of risk
and implementing and managing precautionary measures;
(d) the person or company carrying out the water treatment;
(e) details of maintenance such as:
(i) date and result of visual inspection
(ii) date of cleaning and disinfection
13
(iii) date of chemical treatment
(iv) date of biocidal treatment
(v) monitoring for
- standard plate count (date sampled and result)
- legionella bacteria count (date sampled and result)
(vi) remedial work (if required) and date executed.
Each activity (i)-(vi) shall be authenticated by signature of the person who carried out the
task.
13.3 Record books shall be kept for at least two (2) years after their last entry.
14 Action plan for an outbreak
14.1 If an outbreak of legionnaire’s disease has occurred or is suspected to have
occurred, it shall immediately be notified to:
Commissioner of Public Health
c/o Quarantine & Epidemiology Department
Ministry of the Environment
40 Scotts Road
Singapore 228231
14.2 In the event or on the suspicion of an outbreak of legionnaires' disease
implicating a cooling tower, an investigating team from the Ministry of the
Environment shall require the following under the Infectious Diseases Act
Cap. 137:
(a) a building plan showing the details of all the floors, and location of
the cooling towers and fresh air inlets to the building;
(b) the cooling tower circuit in a diagram form;
(c) the cooling tower maintenance records; and
(d) any other information required for the epidemiological investigation.
14
14.3 The implicated cooling tower shall not be drained or disinfected before
water samples are taken by the team.
14.4 The following emergency procedure shall take place urgently:
(a) cordon off the cooling tower;
(b) switch off fan of the cooling tower immediately;
(c) switch off circulation pump as soon as practical;
(d) discontinue the regular chemical treatment programme (corrosion
inhibitor, scale inhibitor) and shut off the chemical feeders; and
(e) keep all personnel clear of the tower.
14.5 The investigating team shall require the immediate cleaning and
disinfection of the implicated cooling tower, under the Environmental
Public Health (Cooling Towers and Water Fountains) Regulations 2001,
as follows:
(a) add sodium hypochlorite to the system water to obtain a measured
concentration of 50 mg/litre of free chlorine. Add a suitable
biodispersant immediately or at the same time as sodium
hypochlorite;
(b) circulate the system water with the fans off for a period of at least 6
hours, maintaining the free chlorine level at an absolute minimum of
20 mg/litre at all times;
(c) after 6 hours, dechlorinate and drain the system;
(d) undertake manual cleaning of the tower, sump and distribution
system with cleaning staff wearing suitable protective equipment as
set out in section 18.2;
(e) refill with fresh water, add sodium hypochlorite;
(f) recirculate without using fan, at 20 mg/litre of free chlorine for 6
hours;
(g) dechlorinate and drain the system;
(h) refill, recirculate, and take samples for testing; and
15
(i) re-commission the system when test results show absence of
legionella bacteria.
15 Water sampling and bacteriological monitoring
15.1 A regular testing programme for legionella bacteria (including total
bacteria count) shall be carried out to check the efficacy of the water
treatment regime at the following intervals:
Standard plate count - At least once a month.
Legionella bacteria count - At least once in every three months.
15.2 The water sample shall be taken before the dosing of biocide. If
disinfection is carried out, the water sample shall be taken no less than 3
days after disinfection to ensure effectiveness of the treatment.
15.3 The water sample shall be taken from the cooling tower pond. The systems
must be operating, and water circulated through the system for at least one
hour prior to collection of the sample.
15.4 The water sample shall not be collected:
(a) near a make-up water inlet; or
(b) with sediments that have been deliberately stirred up.
15.5 The samples shall be transported to the laboratory in a cooler with ice
packs to maintain sample temperature of 6 to 18°C within the same
working day.
15.6 The government laboratory or any laboratory conducting the tests shall
have official approval from the Commissioner/accreditation from the
Ministry of Health.
15.7 One water sample shall be taken from each cooling tower. A laboratory
report shall be supplied for each cooling circuit.
15.8 The laboratory reports shall be submitted to:
Commissioner of Public Health
c/o Environmental Health Department
16
Ministry of the Environment
40 Scotts Road
Singapore 228231
at the stipulated intervals set out in section 15.1. Each report shall be
submitted together with information on the maintenance of the system set
out in Appendix D for each cooling system.
15.9 The routine microbiological monitoring of cooling systems for legionella
bacteria shall not be used to replace sound engineering practices combined
with a regular maintenance and cleaning programme.
16 Enforcement action for legionella bacteria and standard plate count
contamination
16.1 The interpretation for various levels of legionella bacteria and standard
plate count contamination and the action to be taken by the Ministry of the
Environment under the Environmental Public Health (Cooling Towers and
Water Fountains) Regulations 2001 against the building
owner/management corporation shall be as follows:
Table 1
Legionella
bacteria count
(cfu/millilitre)
Interpretation Action
(a) <10 Maintenance
practices may not
be satisfactory
Advisory letter to rectify maintenance
programme, monitor and follow-up.
(b) >10 - <1000 Potentially
hazardous
situation
Enforcement action will be taken
under the Environmental Public
Health (Cooling Towers and Water
Fountains) Regulations 2001.
(c) ≥ 1000 Serious condition Order under Environmental Public
Health (Cooling Towers and Water
17
Fountains) Regulations 2001 to shut
down the system immediately,
decontaminate, clean and disinfect,
monitor and follow-up.
cfu = colony forming unit
Table 2
Standard
plate count
(cfu/millilitre)
Interpretation Action
(a) >100,000 Potentially
hazardous
situation
Enforcement action will be taken
under the Environmental Public
Health (Cooling Towers and Water
Fountains) Regulations 2001.
cfu = colony forming unit
16.2 The remedial measures for Table 1 (a) & (b) and Table 2 (a) above shall be
carried out not later than 24 hours after receiving the information. If
legionella bacteria are again detected, the procedures shall be repeated
until the system is free from contamination.
16.3 In the event that the advisory or warning is not heeded and subsequent
testing by the Ministry of the Environment shows that the legionella
bacteria contamination has not improved or worsened, the system shall be
shut down under the Environmental Public Health (Cooling Towers and
Water Fountains) Regulations 2001.
18
PART IV
WORKER SAFETY
17 Training
17.1 Persons carrying out maintenance and water treatment shall undergo inhouse
training to achieve an appropriate level of knowledge.
17.2 Training shall include:
(a) operations of cooling systems;
(b) principles of water treatment;
(c) maintenance of records;
(d) safety precautions; and
(e) legislations.
19
18 Personal protection of workers
18.1 All workers carrying out maintenance of cooling towers shall be informed
of the risk of legionnaires’ disease, and instructed on the proper use of
personal protective equipment.
18.2 The minimum equipment needed to protect the worker from exposure to
potential hazards according to the type of job shall be:
20
Job
Potential
hazard Personal protective equipment
Inspection Aerosol Half face respirator, capable of filtering
smaller than 5μm particulates, ordinary
work clothing.
Water treatment Aerosol,
chemical
mist
Half face respirator as above, rubber or
vinyl gloves, boots, goggles.
High pressure spraying Aerosol Half face respirator, waterproof
overalls, rubber or vinyl gloves, boots,
goggles or face shield.
Cleaning and chemical
treatment with sodium
hypochlorite solution
12%
Chemical
mist
Full face respirator with canister,
waterproof overalls, rubber or vinyl
gloves and boots.
18.3 When chemical accidentally come in contact with skin, the affected area
shall be immediately flushed with plenty of clean water.
18.4 Workers shall practise a high standard of personal hygiene. Adequate
washing facilities shall be provided and made easily accessible.
18.5 Eating, drinking and smoking shall be prohibited during maintenance
work.
18.6 Hands shall be washed and dried before eating, drinking or smoking.
18.7 Workers exposed to hazardous substances and engaged in processes listed
in sections 10 and 11 shall undergo regular health surveillance with a
medical practitioner.
18.8 In the event that the worker develops respiratory, cutaneous and other
symptoms when exposed to hazardous chemicals, immediate medical
attention shall be sought.
21
APPENDIX A
REGISTRATION OF COOLING TOWERS
1. Address of premises where
cooling towers are installed:
2. Particulars of owner of premises/management corporation of the premises:
Name:
Residential/Business address:
Telephone No.: (O) (H)
3. Number of cooling towers at the premises:
4. Particulars of each
cooling tower:
Ref No. Location
1
2
3
4
5
6
7
8
9
10
(attach a separate sheet if more than 10 cooling towers)
Submitted by: Name:
Address:
Tel No.: Date:
(an original copy shall be sent to: Commissioner of Public Health
c/o Environmental Health Department
Ministry of the Environment
40 Scotts Road
Singapore 228231)
APPENDIX B
22
ALLOWABLE LIMITS FOR TRADE EFFLUENT DISCHARGE
TO A PUBLIC SEWER
(Sewerage and Drainage (Trade Effluent) Regulations 1999)
Allowable limits
Temperature of discharge 45OC
pH value 6-9
BOD (5 days at 20OC) 400
COD 600
Total suspended solids 400 mg/L
Total dissolved solids 3,000 mg/L
Chloride (as chloride ion) 1,000 mg/L
Sulphate (as SO4) 1,000 mg/L
Sulphide (as sulphur) 1 mg/L
Cyanide (as CN) 2 mg/L
Detergents (linear alkylate sulphonate as
methylene blue active substances) 30 mg/L
Grease and oil 60 mg/L
Arsenic 5 mg/L
Barium 10 mg/L
Tin 10 mg/L
Iron (as Fe) 50 mg/L
Beryllium 5 mg/L
Boron 5 mg/L
Manganese 10 mg/L
Phenolic compounds (expressed as phenols) 0.5 mg/L
*Cadmium 1 mg/L
*Chromium (trivalent and hexavalent) 5 mg/L
*Copper 5 mg/L
*Lead 5 mg/L
*Mercury 0.5 mg/L
*Nickel 10 mg/L
*Selenium 10 mg/L
*Silver 5 mg/L
*Zinc 10 mg/L
*Total metal 10 mg/L
* where two or more of the metals are present, the
concentration in the trade effluent shall not exceed 10 mg/L.
APPENDIX C
23
CHECKLIST FOR ASSESSMENT OF HEALTH RISK OF
COOLING TOWERS
(A separate form shall be used for each cooling tower)
Site address: …………………………………………………………………………..
Reference number of cooling tower: ….……..
1 Registration
1.1 Is the cooling tower registered with Ministry of the Environment? (YES)
2 Water supply and discharge
2.1 Is the water supply from PUB or approved by Commissioner? (YES)
2.2 Is the effluent discharged into a public sewer? (YES)
3 Location
3.1 Is the cooling tower located in a position:
(a) that is near a fresh-air intake to an air-conditioning or ventilating
system?
(NO)
(b) that it is possible for wind to carry the sprays/aerosols into the
windows of an adjacent building?
(NO)
4 Record keeping
4.1 Is there a record/logbook for inspection by Ministry of the Environment? (YES)
5 Cooling tower
5.1 Are all parts of the cooling tower accessible for maintenance? (YES)
5.2 Is there an accessible sampling point at:
(a) cooling tower pond? (YES)
(b) bleeding point? (YES)
5.3 Is the pack:
(a) made from natural materials e.g. wood?
(b) clean/scale free/no slime?
(c) easily cleaned and disinfected?
(NO)
(YES)
(YES)
5.4 Are natural rubbers used as seals or caskets? (NO)
5.5 Is the aerosol creation low? (YES)
24
5.6 When the system is operating at full load, is there excessive
drift from the cooling tower discharge?
(NO)
5.7 Are there drift eliminators? (YES)
Are they securely and firmly fitted? (YES)
6 Maintenance
6.1 Is there a regular maintenance programme in operation? (YES)
6.2 Is the cooling tower and the entire distribution system cleaned
and disinfected at least once every six months.
(YES)
7 Water treatment
7.1 Is there a water treatment programme to control:
(a) scale?
(b) slime?
(c) corrosion?
(d) sludge/algae?
(e) microorganisms (including legionella bacteria)?
(YES)
(YES)
(YES)
(YES)
(YES)
7.2 Are the following apparent within the cooling tower:
(a) corrosion?
(b) fouling?
(c) debris, foam, sludge or slime?
(NO)
(NO)
(NO)
7.3 Is the cooling water clear/clean, without silt/scum/foam? (YES)
8 Monitoring
8.1 Is there a regular water treatment for monitoring? (YES)
8.2 Are standard plate counts high (>100,000 cfu/ml)? (NO)
8.3 Are legionella bacteria detected in the system (>10 cfu/ml)? (NO)
8.4 Are the results of bacteriological monitoring routinely
conveyed to Ministry of the Environment?
(YES)
( ) correct answer in bracket
Assessed by: Name:
Address:
Tel. No.: Date:
APPENDIX D
A RECORD OF RESPONSIBILITIES AND ACTIVITIES TO CONTROL
LEGIONELLA BACTERIA IN A SPECIFIED COOLING SYSTEM
25
1. Building: Name:
Address:
Ownership: Government/Statutory Board/Private*
2. Building owner/manager: Name:
Address:
3. Location/Ref. No. of cooling tower:
4. Maintenance contractor: Name:
Address:
5. Water treatment specialist: Name:
Address:
6. Previous cleaning and disinfection: Date:
7. Biocidal treatment for legionella:
(a) Name of biocides: 1.
2.
(b) Schedule of treatment: Continuous/slug or shot* dose method
(c) If slug/shot dose method is used,
date of previous treatment: Date:
8. Water sampling for legionella bacteria test: Date:
9. Laboratory report submitted by: Name:
Company:
Tel No.: Date:
* delete where necessary
26
APPENDIX E
REFERENCES
1. National Health Service Estates, UK. Health Technical Memorandum 2040.
The Control of Legionellae in Healthcare Premises - a Code of Practice, 1993.
2. Health and Safety Commission, UK. The Prevention or Control of Legionellosis
(including Legionnaires’ Disease) - Approved Code of Practice, 1995.
3. Health and Safety Commission, UK. Control of Substance Hazardous to Health
Regulations - Approved Codes of Practice, 1994.
4. Health and Safety Commission, UK. The Control of Legionellosis including
Legionnaires’ Disease, 1993.
5. The Chartered Institution of Building Services Engineers, UK. Technical
Memoranda TM13: 1991. Minimising the Risk of Legionnaires’ Disease, 1991.
6. The Industrial Water Society, UK. Cooling Water Treatment - a Code of
Practice, 1994.
7. The Industrial Water Society, UK. Guide to Risk Assessment for Water
Services, 1994.
8. Department of Health. Report of the Expert Advisory Committee on Biocides,
1989.
9. Department of Employment, UK. Health and Safety - the Notification of
Cooling Towers and Evaporative Condensers Regulations, 1992.
10. British Association for Chemical Specialities, UK. A Code of Practice - the
Control of Legionellae by the Safe and Effective Operation of Cooling Systems,
1989.
11. Council of Standards Australia. Control of Microbial Growth in Air Handling
and Water Systems in Buildings, 1992.
12. Standards Association of Australia. Australian Standard. Air-handling and
Water Systems of Buildings - Microbial Control (AS 3666), 1989.
27
13. New South Wales Health Department, Australia. Code of Practice for the
Control of Legionnaires’ Disease.
14. World Health Organisation. Epidemiology, Prevention and Control of
Legionellosis; Memorandum from a WHO meeting. Bulletin of the World
Health Organisation, 1990; 68: 155-64.
28
APPENDIX F
GLOSSARY OF TERMS
Aerosol A suspension in gaseous medium of solid particles, liquid particles
or solid and liquid particles having negligible falling velocity.
Airconditioning
A form of air treatment whereby temperature, humidity, ventilation
and air cleanliness are all controlled within limits determined by the
requirements of the air-conditioned enclosure.
Air intake Any opening through which air is admitted to an air-handling system
in a building.
Algae Small, usually aquatic plants which require light to grow.
Biocide A chemical capable of killing living microorganisms.
Bleed Water deliberately removed from a cooling system to control the
concentration factor of dissolved solids.
Clean Visually free of sludge, slime, algae, fungi, rust, scale, dust, dirt and
any foreign material.
Competent
person
One who is adequately qualified and experienced to provide
supervision for the operation and maintenance of cooling towers.
Cooling tower Any device in which atmospheric air is passed through sprayed water
in order to lower the temperature of the water by evaporative cooling.
Corrosion
inhibitors
Chemicals designed to prevent or slow down the waterside corrosion
of metals.
Deadleg A length of pipe, normally closed at one end, or ending at a fitting.
Disinfection Reduction of population of micro-organisms using chemical or
physical means.
Dispersant A chemical usually added with other treatment chemicals to loosen
organic material adhering to surfaces and prevent accumulation of
sludges.
Drift The water aerosol which emerges from the airflow outlet of a cooling
tower.
29
Drift eliminator Equipment containing a complex system of baffles designed to
remove water droplets from cooling tower air passing through it.
Filtration The process of separating solids from a liquid by means of a filter
media through which only the liquid passes.
Fouling Organic growth or other deposits on heat transfer surfaces causing
loss of efficiency.
Legionella A genus of bacterium which is ubiquitous in aqueous environments
and found in water systems in the built environment, including
cooling systems that are not properly or regularly maintained. It
comprises numerous species. Legionella pneumophila is the most
common causative organism of legionnaires’ disease.
Legionnaires’
disease
A rare form of severe pneumonia caused by Legionella pneumophila.
It affects principally older men, especially smokers or persons whose
defences are already impaired by serious disease.
Make-up water Fresh water added to circulating water to compensate for losses, by
evaporation, bleed, drift or leakage.
Outbreak Two or more cases of legionnaires’disease linked by time and place.
Premises All non-domestic premises used for or in connection with trade,
business or other undertaking.
Scale inhibitor Chemical added to water to inhibit formation of scale.
Slime A mucous-like material which is produced as part of an organism’s
metabolism and allows adherence of protective layer to surfaces.
Sludge A general term for soft mud-like deposits on heat-transfer surfaces or
other important sections of a cooling system.
Windage Physical loss of water from the base of a cooling tower caused by
wind of unusual pattern passing through it.
CONTENTS
FOREWORD 1
ACKNOWLEDGEMENTS 2
PART I: PRELIMINARY
1. Purpose 3
2. Scope and application 3
3. Responsibility 3
PART II: COOLING TOWERS IN BUILDINGS
4. Cooling tower design and construction 5
5. Location of cooling tower 6
6. Source of water 6
7. Discharge of water 6
8. Commissioning and operation 7
PART III: SERVICING, MAINTENANCE AND
MONITORING OF COOLING SYSTEM
9. Maintenance 8
10. Cleaning and disinfection 9
11. Water treatment 10
12. Biocide 11
13. Record keeping 12
14. Action plan for an outbreak 13
15. Water sampling and bacteriological monitoring 15
16. Enforcement action for legionella and standard plate count contamination 16
PART IV: WORKER SAFETY
17. Training 19
18. Personal Protection of workers 19
Appendices
A. Information required for the registration of cooling 21
towers
B. Allowable limits for trade effluent discharge to a 22
public sewer
C. Checklist for assessment of health risk of cooling 23
towers
D. A record of responsibility and activities to control 25
legionella bacteria in a specified cooling system
E. References 26
F. Glossary of terms 28
1
FOREWORD
Legionnaires’ disease is an acute bacterial infection of the lower respiratory
tract. Among the elderly and persons whose body resistance is weakened by other
concurrent illnesses, the infection can be fatal. The disease is caused by the inhalation
of tiny water droplets containing the legionella bacteria which thrive in poorly
maintained cooling towers. Proper maintenance of cooling towers with regular
mechanical cleaning, and routine treatment with biocides is therefore important and
necessary.
To minimise the risk of outbreaks of legionnaires’ disease in Singapore, the
Institute of Environmental Epidemiology, Ministry of the Environment, in consultation
with other government departments and professional bodies, formulated this Code of
Practice for the control of legionella bacteria in cooling towers. It is intended for
building owners/management corporations of centrally air-conditioned offices and
factories, contractors involved in the servicing and maintenance of cooling towers, and
others responsible for the design, operation and maintenance of air-conditioned
buildings.
This document specifies the design, construction and location of cooling
towers. It also provides guidelines on servicing and maintenance of cooling towers. It
includes a checklist for assessment of health risk of cooling towers and emergency
remedial measures in the event of an outbreak.
Building owners/management corporations are reminded that based on the
Environmental Public Health (Cooling Towers and Water Fountains) Regulations
2001, it is an offence to operate cooling towers that are grossly contaminated and pose
a health hazard.
WANG NAN CHEE
COMMISSIONER OF PUBLIC HEALTH
MINISTRY OF THE ENVIRONMENT
SINGAPORE
2
ACKNOWLEDGEMENTS
The advice, comments and contributions of the following departments and
professional bodies are gratefully acknowledged:
Quarantine & Epidemiology Department, Ministry of the Environment
Prosecution & Contracts Unit, Ministry of the Environment
Drainage Department, Ministry of the Environment
Environmental Health Department, Ministry of the Environment
Central Building Plan Unit, Ministry of the Environment
Sewerage Department, Ministry of the Environment
Pollution Control Department, Ministry of the Environment
Building Engineering Division, Building and Construction Authority
Department of Industrial Health, Ministry of Manpower
Medical Laboratory Board, Ministry of Health
Pathology Department, Singapore General Hospital
Singapore Association of ASHRAE Members
Singapore Institute of Architects
Institution of Engineers Singapore
Singapore Contractors Association
3
PART I
PRELIMINARY
1 Purpose
1.1 The purpose of this Code of Practice is to provide guidelines for the
prevention and control of legionella bacteria in cooling towers in order
to minimise the occurrence and risk of outbreaks of legionnaires’
disease.
2 Scope and application
2.1 This document applies to all cooling towers in new and existing
premises which are used as shops, offices, trade, business, industry or
for any other purposes in Singapore.
2.2 It is applicable for use at various stages during the inception, design,
upgrading, refurbishment, extension and maintenance of the building.
2.3 In this document, references to specific requirements under the relevant
legislations are made. Failure to comply with these requirements shall
constitute an offence under the respective regulations, and appropriate
enforcement action shall be taken.
3 Responsibility
3.1 It shall be the responsibility of the owner/management corporation of
the premises with cooling towers to:
(a) assess the risk of occurrence of legionnaires’ disease arising from
cooling towers;
(b) set up and manage a programme to minimise the risk of an
outbreak of legionnaires’ disease and monitor the effectiveness of
the programme;
(c) keep records of all activities implemented; and
(d) ensure the safety of operation and maintenance personnel and that
they are adequately trained.
4
3.2 The owner/management corporation shall ensure that persons
designated to carry out the responsibilities specified above are
competent, adequately qualified and experienced. Where the
owner/management corporation lacks the expertise, it shall be delegated
or contracted to consultants with the relevant experience and expertise.
3.3 The owner/management corporation shall ensure that every water
cooling system in the premises is registered with the Ministry of the
Environment, using the form in Appendix A.
3.4 The owner/management corporation shall ensure that there is an
instruction manual for every air-conditioning system incorporating:
(a) a schematic plan of the air-conditioning system;
(b) its operation;
(c) the necessary precautions to be taken specifying checks and their
frequency, and steps to be taken to remedy defects and deficiencies;
and
(d) equipment supplier’s particulars/contact numbers.
5
PART II
COOLING TOWERS OF BUILDINGS
4 Cooling tower design and construction
4.1 At the stage of the construction of the building and the installation of
cooling system, inspection shall be made by competent persons so that the
cooling towers pose minimal health risk to occupants of the building and
members of the public.
4.2 Cooling systems shall be designed and constructed so as to minimise the
release of drift and to aid safe operation, and regular cleaning and
disinfection.
4.3 The design of the cooling system:
(a) shall be simple and practical (deadlegs, loops and bends should be
avoided and redundant pipework removed); and
(b) shall allow for easy access to all parts of the system for inspection,
sampling, cleaning and disinfection.
4.4 A new or refitted cooling tower shall have features that minimise the
formation and release of drift, in particular:
(a) a water distribution system within the cooling tower designed to
create as little spray as possible;
(b) an effective high efficiency drift eliminator; and
(c) an enclosure of the area above the cooling tower pond. This will
reduce the effects of windage that cause the drift to escape through
the sides. It should not be transparent or translucent as sunlight can
promote the growth of algae which is conducive for the growth of
legionella bacteria.
4.5 Construction materials shall be non-corrosive, resistant to chemicals (e.g.
fibre glass, stainless steel), smooth, non-porous, opaque to sunlight and
readily disinfected. Materials used shall not support the growth and
proliferation of microorganisms.
6
4.6 A drain shall be located at the lowest point of the pond with a drain-down
valve so that the entire system can be conveniently and completely
drained.
5 Location of cooling tower
5.1 The cooling tower shall be located at least 5 metres away (measured from
the base of the cooling tower) from air circulating and ventilating inlets,
open windows and occupied areas, pedestrian thoroughfares, trafficable
areas, areas of public access, exhaust discharges from kitchens, air
handling system or other areas where nutrients conveyed from these
systems could assist in the growth of legionella.
5.2 When locating a cooling tower, the influence of adjacent buildings and of
prevailing wind direction and the wind distribution over these buildings
shall be taken into account. It shall be located away from the downwind of
air intakes for the building.
6 Source of water
6.1 The source of make-up water shall be supplied by the Public Utilities
Board water mains or any source as may be approved by the
Commissioner.
7 Discharge of water
7.1 Discharge of effluent water from cooling towers shall be into the public
sewers in accordance to the Sewerage and Drainage Act Cap. 293A.
Approval for connection to sewers shall be obtained from the Central
Building Plan Unit, Pollution Control Department, Ministry of the
Environment.
7.2 The concentration of chemicals in the effluent shall be within the allowable
limits of the Sewerage and Drainage (Trade Effluent) Regulations 1999
administered by the Pollution Control Department, Ministry of the
Environment (Appendix B).
7.3 Water from supply or condensation or other sources in the ventilation or
air-conditioning system shall be discharged into a pipe or drain
incorporating a U-bend and an air break between the condensate drain pipe
7
and the floor trap so that potentially contaminated water is prevented from
being drawn back into the ventilation or air-conditioning system.
8 Commissioning and operation
8.1 The specifications and operations of the air-conditioning system shall be in
accordance to all the provisions of the Singapore Standard Code of
Practice for Mechanical Ventilation and Air-Conditioning in Buildings (SS
CP13: 1999 or any revision thereafter).
8.2 Cooling towers shall be properly commissioned before use to ensure that
they operate correctly and safely.
8.3 The entire air-conditioning system shall be clear of any construction debris
and dirt, and cleaned before operation starts.
8.4 Precautions shall be taken to control the risks during commissioning, start
up and during the normal operation of the system.
8.5 In existing buildings:
(a) Where a cooling tower is out of use for more than five days, it shall
be drained, thoroughly cleaned and disinfected before re-use.
(b) Where a cooling tower is not in use, it shall be drained and kept dry.
8
PART III
SERVICING, MAINTENANCE AND
MONITORING OF COOLING SYSTEM
9 Maintenance
9.1 Cooling towers shall be maintained in a clean working condition and in a
good state of repair. A “good state of repair” would mean that there is no
defect in the operation, and the cooling towers should be free from
physical damage or deterioration which may arise from defects, such as,
rusty pipes.
9.2 Every system shall have a comprehensive maintenance manual that
incorporates:
(a) complete building plans of cooling and ventilation systems;
(b) cleaning methods, decontamination procedures and dismantling
instructions;
(c) procedures for water treatment; and
(d) shutdown and start-up procedures.
9.3 The regular maintenance of the cooling system shall be carried out by
competent persons, familiar with the prevention of any hazard arising from
the work.
9.4 Cooling towers shall be visually inspected at least once a week for any
physical defect, general cleanliness, organic fouling and presence of
physical debris.
9.5 A comprehensive maintenance programme including cleaning, disinfecting
and water treatment for every cooling tower shall be carried out to prevent
legionella bacteria from multiplying and to allow water treatment
chemicals to work more effectively.
9.6 Physical devices incorporating use of copper-silver ionisation, filtration,
ultraviolet light or ozone may be incorporated to complement maintenance,
but they shall not replace a proper and regular maintenance programme.
9
10 Cleaning and disinfection
10.1 Thorough cleaning, disinfection and manual desludging of cooling towers
shall be carried out at least once in six months.
10.2 Cleaning and disinfection shall also be carried out in cooling towers:
(a) that have been contaminated during construction, or by dusts or
organic matter;
(b) that have been shut down for more than five days;
(c) that have been mechanically altered or disrupted in a manner which
may lead to contamination;
(d) at regular intervals where the surrounding environment is dusty or
where the water quality is out of control; and
(e) where the adjacent cooling tower has been implicated as a source of
an outbreak of legionnaires' disease.
10.3 By-pass systems or alternating re-circulating pump systems where water is
stagnated shall be regularly cleaned and disinfected or brought into use.
10.4 The procedures for cleaning and disinfection shall be as follows:
(a) The system water shall be pre-chlorinated to achieve a measured
residual of 5 mg/litre free chlorine, to minimise health risk to
cleaning staff. Circulate water together with a biodispersant, to
enhance the effectiveness of chlorination, for 6 hours, maintaining a
minimum of 5 mg/litre free chlorine at all times. If the circuit pH
value is greater than 8, the measured residual will need to be in the
range of 15-20 mg/litre free chlorine in order to achieve the required
disinfection level. An alternative procedure to provide a more
effective use of chlorine is to introduce a heavy bleed-off for several
hours to reduce the pH of the system and its chlorine content;
(b) The circuit shall be drained and the tower, sump, and distribution
system manually cleaned. Accessible areas of the towers and its
pack shall be adequately washed. Scale and other deposits that have
not been removed shall be dissolved using chemical descalants,
carefully chosen to avoid damage to the circuit/cooling tower.
Cleaning methods which create excessive spray such as high
pressure water jetting shall be avoided. If this is not possible, the
cleaning shall be carried out when the building is unoccupied or in
the case of permanently occupied buildings, windows and air inlets
in the vicinity closed. Staff involved in water jetting shall be
10
adequately trained and wear suitable respiratory protective
equipment set out in section 18.2;
(c) The system shall be refilled with fresh water, and re-chlorinated to
maintain a minimum level of 5 mg/litre free chlorine throughout the
period of 6 hours. A biodispersant shall be used to enhance the
effectiveness of chlorination; and
(d) The system shall be drained and flushed, refilled with fresh water
and dosed with the appropriate start-up level of treatment chemicals,
including biocides.
During the procedure, the cooling tower fans should be switched off.
11 Water treatment
11.1 To control legionella bacteria, the water treatment regime shall prevent or
adequately reduce the amounts of:
(a) scale and corrosion products which might protect legionella bacteria
in the system;
(b) sediments which might prevent water treatment processes from
working effectively; and
(c) other bacteria and microorganisms.
11.2 A complete automatic water treatment shall be installed for accurate
dosing comprising:
(a) a metering pump; and
(b) a chemical dosage pot for feeding the chemicals.
11.3 Slime and algae growth shall be controlled with biocides. If there is a
sudden bloom of slime and algae, an alkaline cleaner to remove and
disperse the growth shall be applied, the system flushed, cleaned, and
biocide redosed.
11.4 The control of silt deposit shall be achieved by a chemical treatment
programme using dispersants or formulated chemicals.
11
11.5 The chemical used in the water treatment programme shall have no
detrimental effect on non-metallic materials such as rubber or epoxy anticorrosive
lining which may be used in the piping system. It shall be
compatible and neutral to the pipework materials.
11.6 No system shall be treated with any chemical or compound for which there
is no test procedure.
11.7 All packaging, storage and handling of chemicals shall be in accordance to
the manufacturer’s recommendation.
A checklist for assessment of health risk of cooling towers is shown in Appendix C.
12 Biocide
12.1 At least two (2) types of biocides shall be used alternately on a weekly
basis to prevent emergence of resistant strains of microorganisms.
12.2 Before setting up a biocidal water treatment programme, it shall be ensured
that the system is clean.
12.3 The ‘shot/slug dose’ method shall be implemented to prevent
microbiological acclimatisation. This involves the addition of the biocides,
alternating them at suitable intervals, directly into the cooling tower basin
using an automatic control system.
12.4 The biocide used to eliminate and control the growth of legionella bacteria
shall comply with the following:
(a) It shall not be a prohibited chemical in the Poisons Act Cap. 234 for
trade effluent discharge to a public sewer;
(b) It shall be effective against a wide range of micro-organisms
(including all legionella bacteria) at the recommended dilutions, and
its effectiveness supported by official independent reports;
(c) It shall be manufactured by the supplier to an independent
specification such as the British Standard 5750 or other approved
equivalent standards;
(d) It shall already have been in widespread use for similar field
application in the country of manufacture for no less than 3 years;
12
(e) It shall be proven to be effective when dosed in accordance to the
manufacturer’s recommendations (frequency, dose strength,
preparation);
(f) It shall have documentation available covering the safety and
effectiveness of the product in recirculating systems;
(g) It shall not interfere with the method used for identification of
legionella bacteria;
(h) It shall be chemically and physically compatible with processed
water and neutral to piping materials.
12.5 The chemicals used and the subsequent end-products of the treatment
programme shall be degradable with minimal hazards to the environment
in the event of accidental spillage or through draining into effluent
treatment plants, meeting all the necessary requirements of the Ministry of
the Environment under the Sewerage and Drainage (Trade Effluent)
Regulations 1999.
13 Record keeping
13.1 A formal record book for every cooling tower with accurate and adequate
information shall be kept and be made available for inspections by officials
from the Ministry of the Environment.
13.2 The record shall include:
(a) a description of the cooling tower such as location, model and
capacity;
(b) the name of the person who ensures that proper records are kept;
(c) the person or company who is responsible for the assessment of risk
and implementing and managing precautionary measures;
(d) the person or company carrying out the water treatment;
(e) details of maintenance such as:
(i) date and result of visual inspection
(ii) date of cleaning and disinfection
13
(iii) date of chemical treatment
(iv) date of biocidal treatment
(v) monitoring for
- standard plate count (date sampled and result)
- legionella bacteria count (date sampled and result)
(vi) remedial work (if required) and date executed.
Each activity (i)-(vi) shall be authenticated by signature of the person who carried out the
task.
13.3 Record books shall be kept for at least two (2) years after their last entry.
14 Action plan for an outbreak
14.1 If an outbreak of legionnaire’s disease has occurred or is suspected to have
occurred, it shall immediately be notified to:
Commissioner of Public Health
c/o Quarantine & Epidemiology Department
Ministry of the Environment
40 Scotts Road
Singapore 228231
14.2 In the event or on the suspicion of an outbreak of legionnaires' disease
implicating a cooling tower, an investigating team from the Ministry of the
Environment shall require the following under the Infectious Diseases Act
Cap. 137:
(a) a building plan showing the details of all the floors, and location of
the cooling towers and fresh air inlets to the building;
(b) the cooling tower circuit in a diagram form;
(c) the cooling tower maintenance records; and
(d) any other information required for the epidemiological investigation.
14
14.3 The implicated cooling tower shall not be drained or disinfected before
water samples are taken by the team.
14.4 The following emergency procedure shall take place urgently:
(a) cordon off the cooling tower;
(b) switch off fan of the cooling tower immediately;
(c) switch off circulation pump as soon as practical;
(d) discontinue the regular chemical treatment programme (corrosion
inhibitor, scale inhibitor) and shut off the chemical feeders; and
(e) keep all personnel clear of the tower.
14.5 The investigating team shall require the immediate cleaning and
disinfection of the implicated cooling tower, under the Environmental
Public Health (Cooling Towers and Water Fountains) Regulations 2001,
as follows:
(a) add sodium hypochlorite to the system water to obtain a measured
concentration of 50 mg/litre of free chlorine. Add a suitable
biodispersant immediately or at the same time as sodium
hypochlorite;
(b) circulate the system water with the fans off for a period of at least 6
hours, maintaining the free chlorine level at an absolute minimum of
20 mg/litre at all times;
(c) after 6 hours, dechlorinate and drain the system;
(d) undertake manual cleaning of the tower, sump and distribution
system with cleaning staff wearing suitable protective equipment as
set out in section 18.2;
(e) refill with fresh water, add sodium hypochlorite;
(f) recirculate without using fan, at 20 mg/litre of free chlorine for 6
hours;
(g) dechlorinate and drain the system;
(h) refill, recirculate, and take samples for testing; and
15
(i) re-commission the system when test results show absence of
legionella bacteria.
15 Water sampling and bacteriological monitoring
15.1 A regular testing programme for legionella bacteria (including total
bacteria count) shall be carried out to check the efficacy of the water
treatment regime at the following intervals:
Standard plate count - At least once a month.
Legionella bacteria count - At least once in every three months.
15.2 The water sample shall be taken before the dosing of biocide. If
disinfection is carried out, the water sample shall be taken no less than 3
days after disinfection to ensure effectiveness of the treatment.
15.3 The water sample shall be taken from the cooling tower pond. The systems
must be operating, and water circulated through the system for at least one
hour prior to collection of the sample.
15.4 The water sample shall not be collected:
(a) near a make-up water inlet; or
(b) with sediments that have been deliberately stirred up.
15.5 The samples shall be transported to the laboratory in a cooler with ice
packs to maintain sample temperature of 6 to 18°C within the same
working day.
15.6 The government laboratory or any laboratory conducting the tests shall
have official approval from the Commissioner/accreditation from the
Ministry of Health.
15.7 One water sample shall be taken from each cooling tower. A laboratory
report shall be supplied for each cooling circuit.
15.8 The laboratory reports shall be submitted to:
Commissioner of Public Health
c/o Environmental Health Department
16
Ministry of the Environment
40 Scotts Road
Singapore 228231
at the stipulated intervals set out in section 15.1. Each report shall be
submitted together with information on the maintenance of the system set
out in Appendix D for each cooling system.
15.9 The routine microbiological monitoring of cooling systems for legionella
bacteria shall not be used to replace sound engineering practices combined
with a regular maintenance and cleaning programme.
16 Enforcement action for legionella bacteria and standard plate count
contamination
16.1 The interpretation for various levels of legionella bacteria and standard
plate count contamination and the action to be taken by the Ministry of the
Environment under the Environmental Public Health (Cooling Towers and
Water Fountains) Regulations 2001 against the building
owner/management corporation shall be as follows:
Table 1
Legionella
bacteria count
(cfu/millilitre)
Interpretation Action
(a) <10 Maintenance
practices may not
be satisfactory
Advisory letter to rectify maintenance
programme, monitor and follow-up.
(b) >10 - <1000 Potentially
hazardous
situation
Enforcement action will be taken
under the Environmental Public
Health (Cooling Towers and Water
Fountains) Regulations 2001.
(c) ≥ 1000 Serious condition Order under Environmental Public
Health (Cooling Towers and Water
17
Fountains) Regulations 2001 to shut
down the system immediately,
decontaminate, clean and disinfect,
monitor and follow-up.
cfu = colony forming unit
Table 2
Standard
plate count
(cfu/millilitre)
Interpretation Action
(a) >100,000 Potentially
hazardous
situation
Enforcement action will be taken
under the Environmental Public
Health (Cooling Towers and Water
Fountains) Regulations 2001.
cfu = colony forming unit
16.2 The remedial measures for Table 1 (a) & (b) and Table 2 (a) above shall be
carried out not later than 24 hours after receiving the information. If
legionella bacteria are again detected, the procedures shall be repeated
until the system is free from contamination.
16.3 In the event that the advisory or warning is not heeded and subsequent
testing by the Ministry of the Environment shows that the legionella
bacteria contamination has not improved or worsened, the system shall be
shut down under the Environmental Public Health (Cooling Towers and
Water Fountains) Regulations 2001.
18
PART IV
WORKER SAFETY
17 Training
17.1 Persons carrying out maintenance and water treatment shall undergo inhouse
training to achieve an appropriate level of knowledge.
17.2 Training shall include:
(a) operations of cooling systems;
(b) principles of water treatment;
(c) maintenance of records;
(d) safety precautions; and
(e) legislations.
19
18 Personal protection of workers
18.1 All workers carrying out maintenance of cooling towers shall be informed
of the risk of legionnaires’ disease, and instructed on the proper use of
personal protective equipment.
18.2 The minimum equipment needed to protect the worker from exposure to
potential hazards according to the type of job shall be:
20
Job
Potential
hazard Personal protective equipment
Inspection Aerosol Half face respirator, capable of filtering
smaller than 5μm particulates, ordinary
work clothing.
Water treatment Aerosol,
chemical
mist
Half face respirator as above, rubber or
vinyl gloves, boots, goggles.
High pressure spraying Aerosol Half face respirator, waterproof
overalls, rubber or vinyl gloves, boots,
goggles or face shield.
Cleaning and chemical
treatment with sodium
hypochlorite solution
12%
Chemical
mist
Full face respirator with canister,
waterproof overalls, rubber or vinyl
gloves and boots.
18.3 When chemical accidentally come in contact with skin, the affected area
shall be immediately flushed with plenty of clean water.
18.4 Workers shall practise a high standard of personal hygiene. Adequate
washing facilities shall be provided and made easily accessible.
18.5 Eating, drinking and smoking shall be prohibited during maintenance
work.
18.6 Hands shall be washed and dried before eating, drinking or smoking.
18.7 Workers exposed to hazardous substances and engaged in processes listed
in sections 10 and 11 shall undergo regular health surveillance with a
medical practitioner.
18.8 In the event that the worker develops respiratory, cutaneous and other
symptoms when exposed to hazardous chemicals, immediate medical
attention shall be sought.
21
APPENDIX A
REGISTRATION OF COOLING TOWERS
1. Address of premises where
cooling towers are installed:
2. Particulars of owner of premises/management corporation of the premises:
Name:
Residential/Business address:
Telephone No.: (O) (H)
3. Number of cooling towers at the premises:
4. Particulars of each
cooling tower:
Ref No. Location
1
2
3
4
5
6
7
8
9
10
(attach a separate sheet if more than 10 cooling towers)
Submitted by: Name:
Address:
Tel No.: Date:
(an original copy shall be sent to: Commissioner of Public Health
c/o Environmental Health Department
Ministry of the Environment
40 Scotts Road
Singapore 228231)
APPENDIX B
22
ALLOWABLE LIMITS FOR TRADE EFFLUENT DISCHARGE
TO A PUBLIC SEWER
(Sewerage and Drainage (Trade Effluent) Regulations 1999)
Allowable limits
Temperature of discharge 45OC
pH value 6-9
BOD (5 days at 20OC) 400
COD 600
Total suspended solids 400 mg/L
Total dissolved solids 3,000 mg/L
Chloride (as chloride ion) 1,000 mg/L
Sulphate (as SO4) 1,000 mg/L
Sulphide (as sulphur) 1 mg/L
Cyanide (as CN) 2 mg/L
Detergents (linear alkylate sulphonate as
methylene blue active substances) 30 mg/L
Grease and oil 60 mg/L
Arsenic 5 mg/L
Barium 10 mg/L
Tin 10 mg/L
Iron (as Fe) 50 mg/L
Beryllium 5 mg/L
Boron 5 mg/L
Manganese 10 mg/L
Phenolic compounds (expressed as phenols) 0.5 mg/L
*Cadmium 1 mg/L
*Chromium (trivalent and hexavalent) 5 mg/L
*Copper 5 mg/L
*Lead 5 mg/L
*Mercury 0.5 mg/L
*Nickel 10 mg/L
*Selenium 10 mg/L
*Silver 5 mg/L
*Zinc 10 mg/L
*Total metal 10 mg/L
* where two or more of the metals are present, the
concentration in the trade effluent shall not exceed 10 mg/L.
APPENDIX C
23
CHECKLIST FOR ASSESSMENT OF HEALTH RISK OF
COOLING TOWERS
(A separate form shall be used for each cooling tower)
Site address: …………………………………………………………………………..
Reference number of cooling tower: ….……..
1 Registration
1.1 Is the cooling tower registered with Ministry of the Environment? (YES)
2 Water supply and discharge
2.1 Is the water supply from PUB or approved by Commissioner? (YES)
2.2 Is the effluent discharged into a public sewer? (YES)
3 Location
3.1 Is the cooling tower located in a position:
(a) that is near a fresh-air intake to an air-conditioning or ventilating
system?
(NO)
(b) that it is possible for wind to carry the sprays/aerosols into the
windows of an adjacent building?
(NO)
4 Record keeping
4.1 Is there a record/logbook for inspection by Ministry of the Environment? (YES)
5 Cooling tower
5.1 Are all parts of the cooling tower accessible for maintenance? (YES)
5.2 Is there an accessible sampling point at:
(a) cooling tower pond? (YES)
(b) bleeding point? (YES)
5.3 Is the pack:
(a) made from natural materials e.g. wood?
(b) clean/scale free/no slime?
(c) easily cleaned and disinfected?
(NO)
(YES)
(YES)
5.4 Are natural rubbers used as seals or caskets? (NO)
5.5 Is the aerosol creation low? (YES)
24
5.6 When the system is operating at full load, is there excessive
drift from the cooling tower discharge?
(NO)
5.7 Are there drift eliminators? (YES)
Are they securely and firmly fitted? (YES)
6 Maintenance
6.1 Is there a regular maintenance programme in operation? (YES)
6.2 Is the cooling tower and the entire distribution system cleaned
and disinfected at least once every six months.
(YES)
7 Water treatment
7.1 Is there a water treatment programme to control:
(a) scale?
(b) slime?
(c) corrosion?
(d) sludge/algae?
(e) microorganisms (including legionella bacteria)?
(YES)
(YES)
(YES)
(YES)
(YES)
7.2 Are the following apparent within the cooling tower:
(a) corrosion?
(b) fouling?
(c) debris, foam, sludge or slime?
(NO)
(NO)
(NO)
7.3 Is the cooling water clear/clean, without silt/scum/foam? (YES)
8 Monitoring
8.1 Is there a regular water treatment for monitoring? (YES)
8.2 Are standard plate counts high (>100,000 cfu/ml)? (NO)
8.3 Are legionella bacteria detected in the system (>10 cfu/ml)? (NO)
8.4 Are the results of bacteriological monitoring routinely
conveyed to Ministry of the Environment?
(YES)
( ) correct answer in bracket
Assessed by: Name:
Address:
Tel. No.: Date:
APPENDIX D
A RECORD OF RESPONSIBILITIES AND ACTIVITIES TO CONTROL
LEGIONELLA BACTERIA IN A SPECIFIED COOLING SYSTEM
25
1. Building: Name:
Address:
Ownership: Government/Statutory Board/Private*
2. Building owner/manager: Name:
Address:
3. Location/Ref. No. of cooling tower:
4. Maintenance contractor: Name:
Address:
5. Water treatment specialist: Name:
Address:
6. Previous cleaning and disinfection: Date:
7. Biocidal treatment for legionella:
(a) Name of biocides: 1.
2.
(b) Schedule of treatment: Continuous/slug or shot* dose method
(c) If slug/shot dose method is used,
date of previous treatment: Date:
8. Water sampling for legionella bacteria test: Date:
9. Laboratory report submitted by: Name:
Company:
Tel No.: Date:
* delete where necessary
26
APPENDIX E
REFERENCES
1. National Health Service Estates, UK. Health Technical Memorandum 2040.
The Control of Legionellae in Healthcare Premises - a Code of Practice, 1993.
2. Health and Safety Commission, UK. The Prevention or Control of Legionellosis
(including Legionnaires’ Disease) - Approved Code of Practice, 1995.
3. Health and Safety Commission, UK. Control of Substance Hazardous to Health
Regulations - Approved Codes of Practice, 1994.
4. Health and Safety Commission, UK. The Control of Legionellosis including
Legionnaires’ Disease, 1993.
5. The Chartered Institution of Building Services Engineers, UK. Technical
Memoranda TM13: 1991. Minimising the Risk of Legionnaires’ Disease, 1991.
6. The Industrial Water Society, UK. Cooling Water Treatment - a Code of
Practice, 1994.
7. The Industrial Water Society, UK. Guide to Risk Assessment for Water
Services, 1994.
8. Department of Health. Report of the Expert Advisory Committee on Biocides,
1989.
9. Department of Employment, UK. Health and Safety - the Notification of
Cooling Towers and Evaporative Condensers Regulations, 1992.
10. British Association for Chemical Specialities, UK. A Code of Practice - the
Control of Legionellae by the Safe and Effective Operation of Cooling Systems,
1989.
11. Council of Standards Australia. Control of Microbial Growth in Air Handling
and Water Systems in Buildings, 1992.
12. Standards Association of Australia. Australian Standard. Air-handling and
Water Systems of Buildings - Microbial Control (AS 3666), 1989.
27
13. New South Wales Health Department, Australia. Code of Practice for the
Control of Legionnaires’ Disease.
14. World Health Organisation. Epidemiology, Prevention and Control of
Legionellosis; Memorandum from a WHO meeting. Bulletin of the World
Health Organisation, 1990; 68: 155-64.
28
APPENDIX F
GLOSSARY OF TERMS
Aerosol A suspension in gaseous medium of solid particles, liquid particles
or solid and liquid particles having negligible falling velocity.
Airconditioning
A form of air treatment whereby temperature, humidity, ventilation
and air cleanliness are all controlled within limits determined by the
requirements of the air-conditioned enclosure.
Air intake Any opening through which air is admitted to an air-handling system
in a building.
Algae Small, usually aquatic plants which require light to grow.
Biocide A chemical capable of killing living microorganisms.
Bleed Water deliberately removed from a cooling system to control the
concentration factor of dissolved solids.
Clean Visually free of sludge, slime, algae, fungi, rust, scale, dust, dirt and
any foreign material.
Competent
person
One who is adequately qualified and experienced to provide
supervision for the operation and maintenance of cooling towers.
Cooling tower Any device in which atmospheric air is passed through sprayed water
in order to lower the temperature of the water by evaporative cooling.
Corrosion
inhibitors
Chemicals designed to prevent or slow down the waterside corrosion
of metals.
Deadleg A length of pipe, normally closed at one end, or ending at a fitting.
Disinfection Reduction of population of micro-organisms using chemical or
physical means.
Dispersant A chemical usually added with other treatment chemicals to loosen
organic material adhering to surfaces and prevent accumulation of
sludges.
Drift The water aerosol which emerges from the airflow outlet of a cooling
tower.
29
Drift eliminator Equipment containing a complex system of baffles designed to
remove water droplets from cooling tower air passing through it.
Filtration The process of separating solids from a liquid by means of a filter
media through which only the liquid passes.
Fouling Organic growth or other deposits on heat transfer surfaces causing
loss of efficiency.
Legionella A genus of bacterium which is ubiquitous in aqueous environments
and found in water systems in the built environment, including
cooling systems that are not properly or regularly maintained. It
comprises numerous species. Legionella pneumophila is the most
common causative organism of legionnaires’ disease.
Legionnaires’
disease
A rare form of severe pneumonia caused by Legionella pneumophila.
It affects principally older men, especially smokers or persons whose
defences are already impaired by serious disease.
Make-up water Fresh water added to circulating water to compensate for losses, by
evaporation, bleed, drift or leakage.
Outbreak Two or more cases of legionnaires’disease linked by time and place.
Premises All non-domestic premises used for or in connection with trade,
business or other undertaking.
Scale inhibitor Chemical added to water to inhibit formation of scale.
Slime A mucous-like material which is produced as part of an organism’s
metabolism and allows adherence of protective layer to surfaces.
Sludge A general term for soft mud-like deposits on heat-transfer surfaces or
other important sections of a cooling system.
Windage Physical loss of water from the base of a cooling tower caused by
wind of unusual pattern passing through it.
Refer to NEA website for the latest update.
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