Commentary SANS 10400:2020 Part T 42
We are going to look at the break down in the changes between the SANS 10400 between Edition 3 and Edition 4. We will explore how they impact the smoke control systems. We discuss the impact on achieving the building occupation compliance.
Edition 4 of The South African National Standard; The application of the National Building Regulations; Part T Fire protection; Edition 4 was approved for publishing in Feb 2020. Edition 4 supersedes SANS 10400-T:2011 (Edition3). The immediate questions are, what changes? How will they affect design solutions going forward?
The change is from the word ROOM with DIVISION. From a language perspective a simple change. Designing smoke ventilation system systems to meet this change will require a measured approach.
An explanation of the words and phrases relating to division:
division: a portion of a building separated from the remainder of such buildings by one or more separating elements.
division wall: an internal wall separates one division from another division in any building. The fire resistance shall not be less than that specified in 4.6 of the regulation.
4.6 Fire resistance of occupancy-separating and division-separating elements. The duration of the fire resistances for occupancy-separating elements can be found in Table 4. Division-separating elements are detailed in Table 5 of SANS 10400
The separation elements are required prevent shared or common ceiling voids. Expansion joints are required to be sealed with a compound which meets the appropriate fire resistance.
Before undertaking the smoke ventilation design the building needs to be classified. A large single level building correctly classified and separated will achieve compliance. A simple and effective smoke ventilation system will meet the requirements detailed in Part T 4.42.
4.42.1 contains three conditions which define the method of ventilation required.
4.42.1.a) steers the designer to the relevant part of EN 12101 allowing for either mechanical or natural ventilation. Usually the correct application of these parts allows an efficient cost-effective solution. A designer well versed in the application of these codes can provide design options with predictable outcomes based on proven testing.
4.42.1.b) defines a specific building condition which may be ventilated using a method specific to the South African environment. The designer needs to determine if the building meets these requirements. The building needs to be a single level building or division. The area of the building or division must have an area less than 2500m². The building cannot be fitted with a sprinkler system. Provided the building meets these requirements the designer is required to meet the following five sub conditions:
4.42.1.b.1) Be provided with a natural ventilation system. A natural ventilation system is a system which uses the energy and buoyancy of the gasses generated by the fire to ventilate the space. The ventilation system may require electrical energy to activate the ventilation equipment. Windows will need to be driven open. Roof ventilators may need to be powered into the open position. The use of electricity in the activation stage of the fire is required for a short period. Electricity is not a requirement for the continual performance of the ventilation system.
4.42.1.b.2) The percentage area calculation is defined based on the classification of the building. The operable area may then be applied to the building or division.
4.42.1.b.3) Defines the position and distribution of the ventilation equipment. The objective is to provide an equilibrium of extraction and reduce the risk of stagnant areas. There has been silence on the supply of replacement air into the division. The regulation cannot be applied without considering engineering principles. Replacement air is required for the functioning of a ventilation system. The ventilated volume needs to be replaced with clean air. In a natural ventilation system providing an inlet area equal to the exhaust area will provide a balanced system.
4.42.1.b.4) The operation of the smoke ventilation system is required to be automatic. Activated from either a heat or smoke detector. Generally, ventilators are fitted with a fusible link system which activates at specific temperature. Should activation be required by the presence smoke a secondary activation system is required, either heat or smoke detection is required to be provided for this activation.
4.42.1.b.5) A clear layer is required to be maintained at 2,5m above the highest occupied area for a minimum time of 600 seconds or the calculated evacuation time. The evacuation time is calculated by the Fire Engineer. Proving this requirement would require a series of calculations to insure the conditions have been met.
4.42.1.c) discusses internal divisions. Any internal division is required to be mechanically ventilated. The internal division is defined as a division which has no external walls and no direct access to the roof of the building. These divisions normally occur in large space shopping malls, multi-level buildings and basements. These buildings are generally viewed as complex buildings. They require the application of international standards which meet the minimum requirement, a 2,5m clear layer above the occupied level, or as may be determined by the Local Authority.
To comply with 4.42.1.c, the designer generally approaches buildings with a rational design. The choice of selecting a code on which to base the rational design rests with the designer. The selected code must meet the minimum requirements according to the South African Regulations. Experienced designers with a wealth of knowledge comfortably tackle complex buildings undertaking rational designs. It is important to apply sound engineering principles in the preparation of a rational design philosophy. The ability to test design solutions using computerized fluid dynamic models provide an accurate performance map of the ventilation systems in a fire condition.
Identification of the operable panels are required. This provides the attending firefighters the ability to position their equipment safely. preventing clashing with equipment which may automatically deploy during the firefighting process.
Equipment used specifically for the smoke ventilation system needs to comply with EN 12101. The independent performance certification of equipment at elevated temperatures provides all stakeholders in the smoke ventilation system peace of mind when the system operates.
Sprinklers are influential on the performance of the smoke ventilation system. Attention is drawn to this inter dependency in the footer of 4.42. Should either system be designed independently without consultation between the designers, each system may negatively impact the other. There is no champion between sprinklers and smoke ventilation systems. Harmony is required, each discipline working together to best protect occupants, product, and buildings in the event of a fire.
I hope this article provides clarity on the impact of the changes from Edition 3 to Edition 4. Should you require assistance with any aspect of smoke control systems connect via email and we can schedule a time to explore solutions.