Smoke control design is an important concept in fire safety and is often misunderstood and misapplied. It should be considered at the same level as a sprinkler system, but rather than simply having to run pipes, builders work shafts or ducting of the correct size and proportion are required and are needed in the right place and they must be fitted with the correct components and controls.
Some more thought may be needed at the fire strategy development stage, rather than simply pointing at using a specialist subcontractor. If brought to the design table too late, the subcontractor will be forced to work with what they are given rather than what is needed for a safe system. This often leads to compromise and the application of fire engineering techniques, which may not have been necessary, if definition had been given at the design stage.
Sometimes, with extended travel distances required, emphasis is placed on clearing smoke from the corridor and the protection of the stairwell (30-50pa across the stairwell door when closed and 1-2m/s velocity through the stairwell door when open) can be overlooked. In this situation a push/pull supply and extract system might be better suited.
Some systems are only designed for means of escape (1m/s through the open stairwell door) and not for firefighting (2m/s). As this really only means a slightly larger fan, then it would not seem to be overcautious in providing one to protect those having to fight the fire.
The stairwell is the main protected area, as people will leave all other floors by this route if required and even if they remain in place, they may not know that there is a fire and leave anyway. Increasingly incidents occurring will spread and people will try and leave anyway.
There are proposals for the use of a building wide alarm system for the fire brigade to use. If this practice comes into place then protected stairwells with a controlled supply of fresh air, preferably from the ground floor, will prevent contamination from rising smoke.
Thinking of firefighters too, it is bad to have an extraction shaft close to the stairwell door, as this, even if it does clear the corridor eventually, still means that smoke is being drawn towards them rather than away. Worse still is if the system has been designed to offset extended travel distances.
In the European region, the EN12101 series of standards provides key information for those designing smoke control systems and selecting or selling associated products. We will not cover the design aspects here but will cover components. These are closely allied with some ISO standards and where there is some equivalence, these are shown. ISO standards are not constrained in content as much as harmonised EN (hEN) standards are.
Smoke control products are all about assemblies. Each assembly achieves the test, not the component parts. The relationship between each part is not proven. So, a smoke control damper, a vent or a window vent includes its actuator and a smoke fan its motor. Simply joining parts together that have been tested with other parts is not acceptable. Therefore, you cannot simply swap and use different actuators and motors. You should not fit actuators or motors to dampers, vents, windows or fans not tested as an assembly.
If the product/assembly falls under the scope of the standard, it must fulfil the requirements of that standard fully and not be a hybrid of components or testing.
The duct and damper standards define single and multi-compartment products and care should taken to select the correct one – unless the duct work is horizontal and leading directly to the outside of the building, it is unlikely that the ducts or associated dampers will be single compartment, as compartment boundaries will be crossed.
For the products test information is sometimes provided or, if not, there is a reference to a full test standard. The standards require that you have a CE mark and this will continue into UKCA marking during the course of 2021. They also require third-party certification to do this. CE marking should generally be seen as a commercial legal requirement for putting the product on the market, but this may be more of a quality/safety mark under UKCA. And it is the responsibility of the manufacturer to understand the rules fully and test and mark accordingly along with supplying a correct Declaration of Performance (DoP). They cannot rely on the third-party certification body in this respect. The scope of each standard must be clearly researched and if the product comes under this scope then it must fulfil the requirements of the standard. If the product is sold under the scope of more than one standard, it must fulfil the scope of all the standards it fulfils and be third-party certified for each. All the correct testing must be fulfilled before a company marks the product or prepares a DoP.
EN12101-1 (ISO 21927-1) addresses smoke curtains which are characterised by moveable screens for the control of smoke and the creation of reservoirs. The standard defines the product and gives all the test requirements and details.
EN12101-2 (ISO 21927-4) is for natural smoke ventilators. These are required in both natural and mechanical systems and are used for letting the smoke out of the building. They will be used on external boundaries (e.g. stairwell head vents, roof vents, windows). The testing is described within the standard. There is an issue here that CE marking can only occur to the 2003 version due to EU rules, but much more information is provided in the 2017 version. They do not maintain compartmentation, as they simply have to open at elevated temperature against various loads where relevant. They are not smoke control dampers that have a requirement to both open and close and have maintenance of compartmentation capabilities when closed and applied in multi compartment applications.
EN12101-3 (ISO 21927-3) describes the requirements and testing for smoke control fans. This is an assembly of the fan and the motor and may be split into families of similar ranges. Issues here can be the application of variable speed control. Most fans are only tested at full speed, not at reduced speeds, where there are some reservations on the continuing operation of the fan at elevated temperature when running slower and at different frequencies of supply. There are also some concerns on older systems presently in place that motors may have deteriorated due to over or, indeed, massive under use. Systems older than 10 years may not even have smoke control fans fitted, so working at elevated temperatures may not even have been tested.
EN12101-7 (ISO 21927-7) defines smoke control duct sections. This is an anomaly because only sections leaving the factory complete are, in theory, allowed to be CE marked. If work is done on site, to add say insulation to the outside of the section, then this may not be CE marked. However, some notified bodies do seem to allow this. For smoke control ducts, the next recourse is to check that the test standard, EN1366-8 has been applied and passed. This requires that the tests in EN1366-1 are done first and the test in EN1366-8. It is advisable to use a third-party certified installer, trained by the manufacturer to instal the ductwork.
EN12101-8 (ISO 21927-8) identifies smoke control dampers. The requirements are described, and the test standard referred to is EN1366-10. Dampers associated with ducts should meet the performance of the duct. Dampers fitted into shaft walls, for instance in apartment blocks should meet the performance of the shaft wall that they are mounted into. Although Approved Document B (ADB) allows the use of fire doors with an Sa classification, care should be taken as the door and actuator have not been tested together. Doors also often have lesser seals at the floor section. Products tested to EN12101-2 and then being presented for an ad hoc fire door test should not be placed on the market, as when used in this application, they fall under the scope of this standard and should meet its requirements, which are different and have associated pressure and cycling performances. Importantly, smoke control dampers are not fire dampers and so-called ‘fire and smoke’ dampers are simply fire dampers with reduced smoke leakage – they have fusible links which would cause dampers to close that need to be open to let smoke out through a protected duct or shaft. It is understood that if working in other markets subject to different rules (e.g. US), smoke dampers may be a different product. On the electrical side, there was to have been a part 9 covering control panels, but this has been effectively put on hold due to EU development rules. Instead ISO 21927-9 should be consulted. In addition, there may be other requirements under the EMC and LVD directives. There is also EN12101-10 covering power supplies.
There are many other subtle requirements for the products that cannot be listed here, but please do further research to understand the issues and do not necessarily take for granted that all the people talking to you are experts – those doing the selections and specifications will have the design responsibility and will have been expected to do more than superficial due diligence, should an incident occur.
For more information, go to www.ventilationfiresmoke.com
About the Author
Paul White is a Director at Ventilation Fire Smoke Limited. He is a recognised expert in the field of fire dampers and smoke control dampers, and this is allied with work on smoke control systems design and install.
You must be logged in to post a comment.