Smoke Control Systems
Fire Systems Ltd can design, install, test and maintain smoke control systems required as stated in Approved Document B (ADB) to protect the communal areas such as the corridors and stairwells in apartment buildings.
The requirement of such systems as AOV’s or smoke ventilation systems is to make it as safe as reasonably possible for residents to escape if necessary and for the fire and rescue service to fight the fire.
The design and performance criteria of the system will vary from building to building according to the layout. However, the principle of what is required will remain the same, and that will be to keep smoke and hot gases out of the corridors and the stairwells.
The most common form of smoke control measures are as follows:
- Natural Smoke Control systems such as Automatic Open Vents (AOV).
- Mechanical forced air ventilation systems.
- Pressurisation smoke control systems.
The implementation of the above system plays a significant role in reducing the spread of the smoke and hot gases spreading vertically through leakage in the vertical barriers.
When reviewing the deaths from fires in residential buildings, the evidence shows that the majority of fatalities is caused by the inhalation of smoke and not the heat from the fire. When considering high rise blocks, the risk is much higher.
When considering primary protection, the corridor or the stairs, the stairs are considered more important, the reason for this is the stairs is the escape route common to all the occupants and will be used for a more extended period during the fire, as well as being the entry and exit for the fire and rescue service.
As our primary objective is to keep smoke off of the stairwell, it is vital that the no apartment door is near the stairwell.
History of Smoke Control Systems
So how did smoke control systems come about? Smoke control is required to keep the hot gases and spoke away from occupants and to keep escape routes clear. We have known for years since fire was first discovered, that if you put a fire in a room, you need to have some extract point to let the smoke out. If you don’t, the room will quickly fill with smoke. The question is how big does the extract point have to be? If the extract point is not big enough, the extraction rate will be lower than the mass flow rate. In other words, there will be more smoke given off from the fire that can be extracted through the extract point, and it fills up with smoke. The secret of smoke control is to determine how big the opening has to be, to prevent the smoke dropping below the design clear layer height. In its simplest form, this is the principle of smoke control. You determine either the area of ventilation required or the extraction rate of the fans.
Smoke extraction has progressed since the early days, and indeed the development of extractors moved on during the Second World War when ventilators were used for blackouts, this enabled the buildings to be blacked-out but still have air being allowed in the building. After the Second World War, Colt developed ventilators for industrial buildings. This is when the sloping roof ventilator was developed, which dramatically reduced installation and maintenance costs. It was also designed to prevent downdraft for blowing smoke back into the building. Now in the 1950s, a major fire at a General Motors plant in America resulted in the development of the world’s first automatic smoke exhaust ventilator. The evolution of manufacturing and the production of large single story industrial buildings needs this type of development. And after another fire in Coventry, at a Jaguar car plant, automatic vents came to Britain. Now, this was expanded to protect warehouses in general, but these were mainly for property protection. It wasn’t until 1968 when a fire in a shopping centre made designers realized how much smoke could be generated in the malls.
They realize how significant the loss of life could be if a fire occurred at peak times when thousands of people were in the building. They realised that they could adopt the system to be used as a life safety system. Now, this led to significant research being carried out, and formula being developed to the determine smoke parameters so that designers could effectively determine what was required in the areas to be protected. Now, the main areas of concern at the time were atrium’s, and this is where the central void rises through two or more storeys, potentially spreading smoke throughout the whole area. Unless, of course, these floors are separated from the atrium by fire resisting construction. In which case, the atrium is mainly a room with a usually high ceiling. It should be readily obvious that a shopping mall of two or more storeys represents a special case of an atrium. It is an atrium with a single class of occupancy. The smoke movement will be similar, the smoke hazards will be similar, and the smoke control solutions can be expected to be similar.
The pivotal problem of both malls and atrium is that smoke entering the void must not be allowed to endanger the safe escape for people in the mall or the atrium itself, or for people in any adjacent space open to the mall or atrium on any story. Modern buildings now tend to look at more innovative designs. These buildings often have included within their design large spaces or voids often integrated with many of the storeys. These large spaces have been described as malls, atrium, arcades and light wells. The generic term for the building type tends to be atrium, and by their very nature, they can often not comply with traditional building regulations approach in terms of horizontal compartmentation and vertical separation. Therefore, where they are proposed, you must demonstrate that they do not pose a risk to the occupants. To do this, there are a number of approaches available, such as BR 368, and PD 7974 part two.