School of the Built Environment Professor J.A. Swaffield FRSE. Emeritus Professor Heriot Watt...

School of the Built Environment

Professor J.A. Swaffield FRSE.

Emeritus Professor

Heriot Watt University, Edinburgh.

Public health challenges for the 21st century.

World Plumbing Day, Holyrood, March 11th 2010


The provision of safe and reliable sanitation faces a range of challenges in the 21st century. These include -

Climate change driven water shortages and excesses will stress both water supply and drainage provision

Migration to the mega cities of the developing world will stress existing infrastructure.

Demographic changes in developed country housing needs will increase water supply demand while climate change dictates water conservation.Lack of planning controls and increased population density in developing cities will endanger public health as installed systems will become stressed and inadequate to meet the applied demand.

The sale of design codes internationally without reference to cultural and regional requirements will confuse designers and lead to poor design.




Meeting these challenges will require coordinated action by organisations working in partnership.

This has been the objective of the World Plumbing Council

Partnerships must be formed that involve the construction industry, manufacturers, building

owners and operators, government and planning authorities, design code organisations, public

health and building services engineering consultants, medical and public health

professionals and research organisations



Two examples of partnerships formed to address public health issues arising from poor drainage

system design exacerbated by increased population density and infection cross contamination due to

system operation and poor or non-existant maintenance will be presented – both

unfortunately taken from Hong Kong but representative of international concerns.


The Pak Tin housing complex in Hong Kong is an example of potential public health risks as a result of increased population density, undersized drainage and poor design.

Show video here


Show video here


This video demonstrates the effect of stack base surcharge in generating positive transient pressures sufficient to destroy an appliance trap seal – in this case a w.c. – leading to the ejection of foul water and waste into the bathrooms on the lower 10 floors of this 50 storey housing complex.


operating appliance

Trap seal deflections

operating appliance

Trap seal deflections

Airflow reduced due to stack base

surcharge

Positive transient affects

all traps


surcharge


surcharge


all traps


all traps


Solution to public health issues as a result of stack base surcharge in a Hong Kong housing block – Active Control

Diverted flow

maintains and

gradually reduces

entrained airflow,

minimising

transient.

Variable volume containment

device or Positive Air

Pressure Attenuator,

PAPA

Positive air pressure transients in stack

eject trap seal water – a health hazard.


The PAPA device developed at Heriot Watt University in conjunction with a major manufacturer, Studor Ltd, has been used in Hong Kong to combat the extreme effects of stack base surcharge caused by under design of the drainage system OR lack of knowledge of likely building population

The following video demonstrate its action.

SHOW Video Here



Laboratory stack base surcharge simulation


Stack base surge may blow trap seals

Test rig includes a trap 20 m above the

stack base. Closure of the airpath generates

a +ve transient

that displaces trap seal water.

PAPA

AAV

Trap

Video viewSurcharge

at stack base.


Multiple PAPA installation enhances control

Two PAPA installed 10m and

40m above stack

base, trap 20 m

higher.

Note PAPA deflates as initial water downflow

established in stack.

Maximum inflation

reduced due to second

unit.

PAPA

AAV

Trap

Video viewSurcharge

at stack base.



Solution – multiple P.A.P.A.TM installation


Airborne spread of SARS in Amoy Gardens Hong Kong 2003

• Virus transmitted via open floor drain traps

• 321 infected cases • 42 deaths

SARS Coronavirus

• World Health Organisation Press Release WHO/70:

• “droplets originating from virus-rich excreta… re-entered into residents apartments via sewage and drainage systems where there were strong upwards air flows, inadequate ‘traps’ and non-functional water seals.”


Route of SARS cross-contamination - 321 infected residents - 42 fatalities

SARS event, Amoy Gardens, Hong Kong, 2003

Shower

Floor DrainWC WHB Shower

Dry TRAPWC WHB

Vent pipe

Stack pipe

ShowerFloor Drain WHBWC


Simulating the inter-apartment route of the SARS cross contamination

Apartment infected with

SARS

Potential route of

contamination to adjacent apartment

blocks

Shower

Floor DrainWC WHB Shower

Floor DrainWC WHB

Vent stack

Vertical Stack

ShowerFloor Drain WHBWC

Apartment infected with

SARS

Post event analysis of the air flow paths confirmed the combination of bathroom fan and dry floor drain as the primary cross contamination route.

-12

-10

-8

-6

-4

-2

0

2

4

6

0 5 10 15 20

Time, seconds.Entr

ain

ed a

irflow

, +

into

room

, -

dow

n s

tack

, litr

es/

seco

nd

Bathroom ventilation fan draws air from the vertical drainage stack through the defective dry trap.

No initial water downflow in vertical stack.

-12

-10

-8

-6

-4

-2

0

2

4

6

0 5 10 15 20

Time, seconds.Entr

ain

ed a

irflow

, +

into

room

, -

dow

n s

tack

, litr

es/

seco

nd

Annular water flow in vertical stack entrains an airflow and overcomes the bathroom fan, resulting in an outflow of air from the bathroom through the defective dry trap.

Upper floor w.c. discharge to vertical stack, water flow increases from 6 to 7 seconds.

-12

-10

-8

-6

-4

-2

0

2

4

6

0 5 10 15 20

Time, seconds.Entr

ain

ed a

irflow

, +

into

room

, -

dow

n s

tack

, litr

es/

seco

nd

W.c. flush steadies and then diminishes to zero.

As the w.c. discharge diminishes the bathroom fan re-establishes the entrained airflow back into habitable space. The airflow carries water droplets and contaminated air into the bathroom.

-12

-10

-8

-6

-4

-2

0

2

4

6

0 5 10 15 20

Time, seconds.Entr

ain

ed a

irflow

, +

into

room

, -

dow

n s

tack

, litr

es/

seco

nd

Process is repeated for each consecutive w.c. flush so that an air exchange between the bathroom and the stack is established.

-12

-10

-8

-6

-4

-2

0

2

4

6

0 5 10 15 20

Time, seconds.Entr

aine

d ai

rflow

, + in

to r

oom

, - d

own

stac

k,

litre

s/se

cond Modelling

confirms the establishment of an air exchange between the bathroom and the vertical stack.

Simulations using the HWU AIRNET model

Route identified by public health teams in Hong Kong.



The 2003 SARS event in Amoy Gardens was a major wake up call for the building services and public health industry. In 2005 a partnership was set to address the detection of depleted trap seals – an industry wide coalition that embodied the objectives of the World Plumbing Council – including

Buro Happold CIBSE SoPHE RBSWPC

Dept of Health IAPMO (US) Studor SNIPEFHWU

The consortium was led by Heriot Watt University and funded by EPSRC and contributions from IAPMO, SNIPEF and Studor.

The outcome is a non-invasive remote defective trap seal detection device already site trialed in a Dundee housing block, Heriot Watt, an RBS building in Glasgow and the Royal Infirmary in Edinburgh. The device will be launched onto the market in 2010.


Low amplitude air pressure transient propagation in drainage and vent systems obeys ALL the laws of surge propagation. Therefore the reflection of a transient by an open or a water

filled trap will vary from -1 to +1. This change in system response to an applied transient may be used to identify the location of the open trap as the propagation speed is known.

A

Defective trap seal identification – a research led response to the SARS analysis.

T18

T19

T21

T2

T3

T4

T5

T9

T12

T13

T14

T15

-60

-40

-20

0

20

40

60

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Time (seconds)

Pre

ss

ure

(m

m W

ate

r G

au

ge

)

Defect Free

Defect at T21


This presentation has been based on the work of the Drainage Research Group at Heriot Watt University and its

partners – working together to further the public health agenda required to meet the challenges of the 21st century.

Thank you for listening.


School of the Built Environment Professor J.A. Swaffield FRSE. Emeritus Professor Heriot Watt...

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Transcript of School of the Built Environment Professor J.A. Swaffield FRSE. Emeritus Professor Heriot Watt...