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SMOKE CONTROL IN HIGH RISES Don’t wait to be told what to do…


David Mowa, Chairman of the Smoke Control Associaon, discusses the issues surrounding smoke control in high rise buildings.


he Grenfell tragedy happened almost 30 years after another devastating fire at London’s King’s Cross Tube station, believed to have been caused by a dropped match, in which 31 people died. Banning smoking in London Underground stations was one of many changes following the fire, as well as replacing wooden escalators. There may well be much to learn from the Grenfell tragedy, leading us to look back in another 30 years and ask, “How did they get it so wrong?”


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With so many tower blocks across the UK, it is essential that smoke controls in high rises are addressed. A high rise is typically more than seven to 10 storeys or 23-30m high.


Any high rise new build will be placed under great scrutiny when it comes to safety, and many existing buildings will need to review their own smoke control systems. Smoke control is particularly important in high rises to protect the escape stair and should feature prominently in the early design, rather than as an afterthought. Older buildings won’t necessarily have lifts or, if they do, they might be reserved for maintenance access. This means the staircases will have been designed with everyday access in mind, making them effectively, vertical corridors. In modern buildings, particularly very tall ones, access between floors will mostly be via the lift, with few people choosing to climb the stairs. This means occupants are less likely to be familiar with using the stairs, and they serve more as an emergency escape route.


Inhalaon of smoke


The biggest cause of fire fatalities is not the fire itself, but the inhalation of smoke. The main focus of smoke control systems is the areas that occupants will use to escape during an emergency, such as the corridors, staircases and common areas.


The build up of smoke in enclosed spaces


creates two main problems. The first is the lack of visibility, as thick smoke will quickly obscure emergency exits. This exacerbates the second problem, as the occupants become disorientated exposing them to smoke inhalation. Keep these areas clear of smoke and the occupants have more chance of survival. Smoke control systems are designed to keep escape routes smoke free to aid evacuation and assist firefighters. Designers are often limited in their choice of smoke control systems for tall buildings because the stairs and lobbies are usually landlocked – ruling out automatic opening vents – and minimal space means space for a natural shaft system can be hard to find. However, there are a few design techniques that will help keep smoke away from stairs: uFull-height stair doors are best avoided as they have no down stand above them to stop a ceiling jet. uApartment doors should be offset from facing stair doors so that smoke from the apartment is not directed straight into the staircase. uThe location of the extract should pull smoke away from the stair door, not towards it. uThe top of ventilators should be fitted as high as possible, not just level with the top of the door, as the requirement in AD B is often interpreted.


Stair venlaon


Until 2007, dead-ends were ventilated rather than spaces opening onto stairs (often the same spaces, but not always). The stair ventilator was expected to protect the stair from excess smoke. Ventilation is now provided to the stair and to each lobby or corridor opening onto the stair. Smoke control in other corridors is usually provided by doors to limit smoke spread and no smoke control is provided in the apartments themselves. We have seen a growing popularity for extended length corridors (30m+) in tower blocks. This often relies on just a single staircase, which seriously limits a firefighter’s escape options if a fire spreads quickly down a corridor. In tall buildings,


the stairwells need to remain smoke and heat free and the entire building must be structurally sound for any fire strategy to be successful. Smoke pouring into a stairwell creates a stack effect, which forms a vertical tunnel free to fill the main escape route. A building fire is capable of filling a 10,000sq m area full of smoke within minutes, so without adequate protection the number and width of stairwells is irrelevant, as smoke-logged stairwells are unusable. The Smoke Control Association’s (SCA) 2015 design guide for ventilation systems in residential buildings ensures that any mechanical smoke ventilation system (MSVS) causes ventilation airflow, smoke and combustible fire gases to head away from the sole firefighting stair, protecting firefighters and lessening their exposures to heat flux along their extended approach route. The ventilation methods most commonly used to limit the degree of smoke spread, or to control its effects, in the common areas of buildings, are: uNatural smoke control systems uMechanical smoke control systems uPressure differential systems


For more information on the above systems please contact the Smoke Control Association.


Longer term vision


In her interim report into the Review of Building Regulations and Fire Safety Dame Judith Hackitt drew attention to the widespread culture in relation to building and standards of waiting to be told what to do by regulators rather than taking a proactive responsibility to correct standards. The attitude seems to be one of aiming for minimum compliance rather than a longer term vision to ensure safety for the lifetime of the building. The problems arising from this approach are exacerbated by contractors and designers who enter the market with little understanding of the rigors to which life safety systems should be designed and installed. There will be many systems still in place now that were far from perfect when installed.


www.feta.co.uk/associations/hevac/specialist-groups/smoke-control-association


26 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MAY 2018


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