Smoke control in high-rise residential buildings is an important and, sadly, topical issue. Having recently written a post about the talk that I gave to the Institute of Mechanical Engineers on smoke control in general, I now want to focus on high-rise residential buildings , a subject that I also addressed with the engineers and, in particular, in the talk I gave to Northern Ireland Building Control Officers in Armagh.
In the wake of Grenfell, we all realise how vital this issue is but it is also complex. I thought it was worth describing some basic points as well as some more detailed ones. I explained the different requirements set out in Approved Document B of the Building Regulations for different heights of buildings. These run through the gamut from the lowest buildings, below 11m in height, which only need a vent at the top of the stairs, to buildings above 50m. These need a fire-fighting core plus sprinkler protection and a wet riser.
There is an even taller category, sometimes referred to as ‘super tall’ which are beyond the scope of Approved Document B. Instead, they need a fire-engineered approach.
In my talk I set out in detail the requirements for different building heights. For example, natural automatic opening vents are permitted on buildings up to 30m high.
I talked about the difference between natural shafts and mechanical shafts and stressed the importance of build quality – that shafts should be fire-rated, non-combustible and well-sealed. And I showed some of the ways in which construction can go wrong, not only contravening regulations but also putting lives at risk.
These examples included a flat where there was no closer on the front door, and a design where all the doors onto the shaft opened together.
I also described the OPV system that Colt offers for smoke control. This simplifies life by controlling the entire system, and makes decisions based on a programmed cause and effect. It can, however, be over-ridden in an emergency.
In this presentation I also looked at some other social factors that could have an impact on smoke control. Cramming and hoarding are serious problems since they both increase the volume of smoke-producing combustible materials and make escape more difficult. I also have concerns about ‘garden cities’ - those buildings with extensive planting on roofs and balconies and the impact that this could have on allowing smoke to escape during a fire. While these buildings have undoubted benefits in other respects, I do not believe that the issue of fire has been considered sufficiently.
Another issue that I discussed was the stack effect, the tendency of warm air to rise through a building and escape at the top, drawing in cooler air at the base. While this has undoubted advantages if employed properly to drive natural ventilation, it must be understood thoroughly in the context of smoke control.
In fact, too extreme a stack effect, with the resulting pressure differences, can have all sorts of undesirable influences, such as increasing heating loads and interfering with the operation of lift doors and revolving entrance doors. Crucially, it can affect smoke control. In particular, it can draw smoke into the stairwell rather than the escape shaft.
As buildings become taller and more densely occupied, there is an impact on the escape strategy. Colt has developed approaches that will increase the allowable travel distance compared to standard ‘compliant’ corridors, by using a mechanical extract system.
Another approach that I demonstrated was the difference between a shaft system and pressurisation. The shaft will only protect the stair on the floor where the fire is. Window failure may have a considerable impact on its behaviour, and it will be limited by operating temperatures.
In contrast, pressurisation may protect the entire stair, the lift and lobby and will not be affected by window failure.
Finally, I ran through the commissioning process, and the all-important maintenance process, which must be just as rigorous. I ended my presentation with a Venn diagram showing how design, installation, selection of equipment and controls, commissioning and maintenance must all be done correctly if smoke control is to be effective.
There was a lot of material in this presentation, and no attendee could be expected to remember all of it. But my aim was to help building control officers appreciate just how important and complex a subject smoke control is, and that, if lives are to be saved, it is essential that everybody involved gets the best professional advice available. Find out more.