Water, Sewage & Effluent January February 2019 | Page 14

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Backflow in a drainage system is also
a serious health threat — specifically,
backflow from the municipal sewage
system.
In a normal house, plumbers provide
a gully between the house and the
municipal sewage connection to act
as an overflow facility so that when
there is a blockage in the municipal
sewer, the sewage can push back
and overflow from the gully of the next
nearest house. This is in accordance
with SANS10400-P deem-to-satisfy
rules. But this can create a serious
health risk and a very unpleasant
situation or ‘nuisance’, as described in
SANS10400-P: P2.
The maintenance services of
municipalities are notoriously below
standard, and municipal maintenance
can take a long time to arrive to clear
the blockage. The occupants of the
house are then forced to live with an
extremely unhealthy situation, with
a potential health threat until the
blockage is cleared. I have personally
seen sewer overflows in the street that
took days before being cleared.
It is important that the design
engineer of a hospital checks where
any backflow may occur — evident
from where the separate horizontal
wastewater discharge pipe exits from
the building, and then the backflow
overflow inside the building and out of
the showers or baths.
The horizontal collector pipes below
the ground floor of a hospital shall be
separate for soil fixtures and separate
for the wastewater fixtures, and if
there is a collector pipe outside of the
building for soil and waste combined,
then an overflow facility is essential —
at least on the wastewater drain pipe
outside the building.
A gully is a very unhygienic fixture.
Most of the time, it is extremely dirty
and germ-ridden and should not be
used in a hospital.
I have used a normal 110mm-diameter
junction in line with a 110mm-diameter
vertical pipe with a cap 150mm above
the ground level; the cap can pop out
easily and release any backflow from
upstream or downstream. I call it a
‘dry overflow facility’, which allows
the backflow to overflow outside the
building, which is normally in a garden
area. It is normally possible to provide a
drain pipe from this area to prevent an
unpleasant situation.
There are so-called backflow
fixtures that work like a non-return
valve in a water system, but this can
only stop the backflow — it cannot
The design and position of the sluice room should also be considered and provided
with an exhaust system for sanitary drainage to prevent contaminated air from entering
passages where medical staff, patients, and visitors walk.
Backflow prevention
A clogged stack (vertical drain) affects
other plumbing fixtures and can cause
contamination.
let it overflow unless it has a facility
such as a pump to force the backflow
out. However, such a facility stops the
flow from the building and causes the
fixtures to overflow inside the building
if used while the downstream pipe
is blocked. Yet, it can be used as a
solution in some cases.
The dry overflow pipe arrangement
with the pop-up cap to allow backflow
from both upstream and downstream
to overflow outside the building, is very
simple and economical, and consists
of only some piping, a 90-degree
junction, a cleaning eye cap, and a
bit of concrete. The pipe arrangement
for the overflow facility can also be
designed to create a double cleaning
eye, to rod both ways.
I have found that it is essential to
have a rodding facility where pipes exit
from the building, and to have a facility
that allows rodding both downstream
and upstream.
Floor drains
There are wonderful floor drains on
the market that do not have a fixed
Water Sewage & Effluent January/February 2019
P-trap, and these are very popular in
kitchens and elsewhere in the hospital.
These floor drains allow you to remove
the top and then have a 110mm (or
less) direct opening into the drainage
system to enable you to do rodding
without having an obstruction such as
a P-trap.
What kitchen designers and other
designers do not realise, is that you
then have a direct connection with the
most awful germs to the rest of the total
sanitary drainage system, right up to
the municipal sewage treatment works
— and all those germs escape through
the open floor drain in the hospital’s
kitchen.
Kitchen floors should not have these
types of floor drains which allow direct
contact with the sanitary drainage
system. Instead, kitchens should be
fitted with floor drains with suitable
metal grids and a channel to discharge
into a water trap, designed in a way that
permanently isolates the kitchen area
from the sanitary drainage system, to
prevent serious contamination of the
kitchen environment.
The ‘old’ building drainage
systems
The previous building regulations for
sanitary drainage systems required full
anti-syphonic ventilation pipes. This
meant that every fixture had to have
what we now call ‘trap ventilation’. The
anti-syphonic pipes were almost an
upside-down replica of the drainage
piping below it.
The pipes were not connected on
the horizontal branch pipes but went
directly upwards from the trap of the
fixture (which is why it is called trap
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