Design of hospital drainage


The design of hospitals is under the control of the Department of Health and as per their document R158.

Guidelines to designing hospital drainage by Vollie Brink

This document is unfortunately not complete and does not address the water and drainage systems of hospitals, it only states that it must be “certified by an “appropriately qualified engineer”. It also notes that the design of a hospital must comply with the National Building Regulations (NBR), where there are no specific regulations for it in R158. Both R158 and the NBR do not have specific regulations for hospital drainage and water systems.

The design therefore must be designed by “an appropriately qualified engineer”, which in terms of the NBR would be a professional registered engineer, which could also be a registered technologist with appropriate experience in hospital services design and it would have to be a “Rational Design”.

SANS10400-P is the NBR design and construction standard for the design of a sanitary drainage system of a building and it contain seven (7) “Regulations” which describe the “performance” of a sanitary drainage system for buildings and its premises.

These performance regulations are compulsory and form the basis of any drainage system for buildings and also the basis for a RD.

Compliance with these performance regulations can be achieved by means of a set of “Deem-To-Satisfy-Rules”, (DTSR) which are basically a “recipe” to follow, which is compulsory if the owner decides to apply it. These DTSR only address two types of buildings, namely housing and office class, and does not address hospitals per se.

However, the DTSR have very good “principles” which can be applied in a RD for a hospital and it is advisable to apply these “principles”.

Some examples are that horizontal drainage of waste water and soil water must never be combined but be separate up to the stack pipe which may be a combined stack pipe.

There must not be long horizontal collector drainage pipes in the ceilings and, where necessary when it is a branch pipe, then not longer than 6m.

It is important to design the system so that backflow from the soil drain cannot push back up into the waste water system, because then sewage could come out of the showers or the baths.

Use the “discharge unit” system to determine the pipe diameters, as it makes provision for “probable simultaneous discharge”. It has worked for centuries all over the world and is reliable.

The second design method to comply with the performance criteria is to do a rational design which may only be done by a registered Engineer / Technologist.

There are a number of other “principles” which we have now included in the latest SANS10400-P with illustrations, soon to be published.

Designing and installing hospital drainage

The important elements in terms of hospital drainage design are as follows:

  1. Appropriate and good durable piping materials.
  2. Appropriate access to and into the piping, this is absolutely critical and the responsibility of the architect in conjunction with the engineer.
  3. Access by means of manholes and inspection chambers is preferred as it allows downstream and upstream cleaning with high pressure water systems.
  4. High pressure cleaning (rodding) is highly preferred as it is more effective and it does not damage the piping.
  5. Minimum external drainage piping diameter preferred to be 150mm ID to prevent blockages.
  6. Access to be situated where drains enter/ exit from buildings in order to be able to rod into the building. This access should preferably be a manhole or inspection chamber.
  7. All bends under floors in ground and above to be long radius consisting of two 45 bends with a meter of piping in between.
  8. Junctions to have a 45 bend with a meter of piping in between the junction and the bend.
  9. Internal building discharge pipes to be separate pipes for soil and separate for waste water to prevent overflow of soil water into the shower or bath or floor drains.
  10. Provide backflow prevention with overflow outside the building where the soil waste water exits or enters the building (this is all on ground level only).
  11. Internal soil and waste water discharge pipes to be 100mm diam. (ID) and minimum gradient 1:60. Please note the ID is essential.
  12. Where waste (50) pipes drop into the floor, it must be connected with a 100mm diam. “floor-stub-stack” to the underfloor 100mm diam. discharge waste water piping.These floor-stub-stacks can be used as access to the under- floor discharge piping system.
  13. All underfloor piping, bends, junctions, change of directions, change of gradient must all be “long-radius” and have appropriate access from above where possible and in service ducts where possible to allow easy access which is critical for maintenance.
  14. Ventilation must be provided on all branches longer than 6m and at least one 100mm diam. open vent pipe at the highest furthest point of the drainage system and ventilation also where necessary elsewhere.
  15. Pumping systems must be provided where really necessary and only if it cannot be avoided and then it must be only a very high quality and very reliable robust pump system with separate maceration system and with appropriate overflow storage capacity.
  16. The pumping main must be high quality, durable piping material such as “Mineflow” or similar type of robust piping.
  17. The pumping system must have full redundancy and have back up power.
  18. Hospitals have equipment that discharge effluent of high temperatures and which require piping that can handle such hot effluent. For this cast iron piping is the best. In some cases a “cooling box” is also required.
  19. Long horizontal pipes in ceilings shall not be allowed. and only if it is a branch pipe not longer than 6m or 10m if it have ventilation.
  20. Floor drains without water discharging into it must be avoided. Where no water can discharge into the drain, a small water supply pipe must be provided with a valve to flush the system daily.
  21. Grease trapping must be provided where necessary and as close as possible from the source of where it is generated. Arrangements must be made for the removal from the site of the grease and fat.
  22. The emergency shower at the ambulance entrance must discharge into a holding tank and the contents be removed from site by an approved company.
  23. Please note the QA is the responsibility of the contractor and not of the engineer. However, the engineer must see that the contractor applies the QA and the engineer must approve the system of the contractor when the contact begins.
  24. The contractor to study and apply the “works information document”.
  25. The “works information document” is a document that contains all the design assumptions, the design decisions, the relevant specifications and relevant information for the contractor and the design and construct elements, such as the plant and equipment such as the pumping systems.
  26. Works Information Document (WID) – there must be no notes all over the drawings as this information must all be recorded in the WID.
  27. Appropriate maintenance by competent persons is, as is training of operational staff, to prevent discharging of material other than normal soil and waste.
  28. Inspection, testing, camera inspections, smoke testing, are all critically important.
  29. Installation from excavation to backfilling must all be in terms of SANS2001.
  30. The as-built situation is the responsibility of the contractor and there must be a survey by a competent surveyor.
  31. The WID must contain all the hand over procedures and requirements with all the guarantees, as well the operation and maintenance requirements
  32. An intelligent Building Management system is essential for a hospital and the pumping systems and other important signals must be monitored.
  33. There are no formal institutional regulations for the design of hospital wet services and this should be addressed nationally.
  34. The plumber shall be PIRB registered and submit a PIRB COC on completion.
  35. The plumber shall maintain the systems for a period of 12 months after completion for a fixed cost.
  36. He shall keep record of all incidents such as drainage blockages and indicate on a drawing where blockages occurred and reasons why.

DRAWINGS:

The drawings shall be comprehensive and as SANS 10400-A and SANS10400-P and contain all information to correctly construct the installations.

Hospital drainage and water systems

CONTRACTORS RESPONSIBILITIES:

The WID must contain all the responsibilities of the contractor and the plumber and it must include the responsibilities of the manufacturers of piping and equipment and what they require from the contractor to enable them to provide their guarantees.

The QA of the contractor / plumber must be approved and the engineer must receive regular QA reports and the contractor must ensure the highest quality.

The contractor must have a dedicated competent QA officer responsible for the QA.

All communication must be writing.

All drainage piping shall be pressure tested, smoke tested and camera inspected during construction and on completion.

Setting out and invert levels and gradients shall all be by a qualified competent surveyor.

 

Author: D.S.Brink Pr. Eng.


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