22 DESIGN: DEAR MR PLUMBER
A new building sanitary
drainage system: Part 2
By
Vollie Brink
The SA National Building Regulations which were promulgated in
the 1970s contained a Part for the design and construction of the
sanitary drainage of buildings, which were called SABS 0400-P,
which later became SANS10400-P. This is Part 2 of a two-part article.
Vollie Brink is one of the
industry’s longest-serving
wet services engineers.
He continues to serve on
SABS committees and
has been involved in the
Green Building Council’s
Green Star rating system.
Brink continues to consult
for various organisations
while enjoying a wellearned
retirement.
There are a number of ‘principles’ which are critically
important, which are as follows:
1. All horizontal pipes shall always in all situations, be
separate for soil-water and separate for wastewater.
The reason for this is, if you have the WC and the
shower and bath and floor drain on the same horizontal
branch or horizontal collector pipe, or any horizontal
pipe, and there is a blockage, then the raw sewage
will come out of the shower or bath or floor drain. This
is not acceptable in any building and does not comply
with the performance criteria as per SANS10400-P
and health and safety act.
2. The ‘antisyphonic’ piping of the past, which has greatly
been rejected, and in many cases been replaced with
the so-called ventilation valve, has served a purpose
which nobody thought about, which is that it actually
draws the highly contaminated air from the piping and
discharges it to the open air.
When a plumber opens an inspection eye on a fixture
such as the WC or any other fixture inside a building,
then all the foul contaminated air from the total
sanitary drainage system escapes into the room and
building.
If the system was provided with ‘trap ventilation’, then
even if you open the cleaning / inspection cap, the foul,
highly contaminated air, would ‘suck’ the air out of the
building. However, it is advisable to install an extractor
fan on the ventilation system.
Most air valves are installed below the windows, which
does not comply with rules for ventilation piping. If
a vent-valve discharges air it must discharge it from
above the highest window and not below it. A vent
valve discharging below the window is a health risk.
3. Pipe ducts in hospitals should have positive air
extraction to keep the foul air from contaminating
the interior of the building. The design of a hospital
sanitary drainage system must be radically changed
and one of the important elements must be to keep the
foul contaminated air from the drainage pipes out of
the building where vulnerable sick people are treated
and this can be easily achieved by rational engineering
design by competent experienced professional
engineers.
As mentioned above, the crux of the design of a
sanitary drainage system for a hospital is to realise
that when the plumber opens an inspection cover, the
foul contaminated air escapes from the piping which
is connected to the total hospital drainage system
AND the total municipal drainage system and directly
contaminate the environment of the hospital, this has
been proven by research.
There are wash hand basins all over the hospital and
every time the plumber unscrews the trap to clean the
piping by rodding, for example, the contaminated air
from the drainage system escapes into the hospital
room.
The challenge is to design the piping with access to
it in such a manner that when the plumber opens
the piping that the foul air cannot contaminate the
environment.
This can only be done by providing pipe ducts with
air extraction when the door is opened or to provide
ventilation from each fixture such as the old type
‘antisyphonic’ piping with or without extract fans.
To discharge the effluent in a sanitary drainage system,
the piping requires a minimum gradient, quantity of
water and air, all correctly engineered.
The ‘deem-to-satisfy-rules’ are not suitable for the
design of a hospital drainage system and the flow
tables are outdated this causes blockages as it does
not provide enough water to convey the effluent.
4. The floor drain is another element that should not be
used in a hospital or in any kitchen of any building, and
the basic reason for this is that when the floor drain
is opened for cleaning then there is an unprotected
opening directly into the drain below from where all
www.plumbingafrica.co.za @plumbingonline @plumbingonline @PlumbingAfricaOnline October 2020 Volume 26 I Number 08