With 53 per cent of fire-related fatalities resulting from individuals being overcome by smoke or toxic fumes, smoke heat exhaust vent systems (SHEVs) make a critical difference by keeping escape routes smoke-free. In multi-occupancy buildings in particular, they enable firefighters to tackle blazes more safely and effectively and can, therefore, make a significant contribution to reducing structural damage.

British Standard guidance varies according to building height and the distance from the furthest apartment entrance door to its nearest escape route. However, life-saving devices and systems should ideally exceed standards and achieve strictly defined performance criteria. Thorough analysis of the proposed fire strategy and design of common escape routes is therefore essential.

Performance criteria and SHEV system design will depend on the layout of corridors and communal areas. As such, a mechanical smoke extraction system will give greater flexibility in terms of floor space utilisation. Indeed, in addition to providing greater efficiency than a natural ventilation system, it can effectively be designed around space constraints. The need for a secondary power supply may increase initial outlay, but this must be set against greater efficiency, design flexibility and the ability to operate in the event of a mains power failure. In addition, it will provide a mechanism for the fire service to stop, override, and ultimately re-set it into a different mode of operation.

There are crucial factors to take into account when designing a smoke control system. In contrast to a natural ventilation system, a mechanical smoke extraction system utilises an extract shaft so that when smoke is detected, the fire damper to the shaft on the fire floor opens while all others remain closed. The vent at the head of the staircase then opens so that a fan at the top of the shaft can extract smoke and prevent its migration into adjacent compartments.

A recent innovation is the modular smoke ventilation system. This gives the architect or M&E consultant the guarantee of flow rate and pressure performance, while offering greater ease and speed of installation. With new build windows often being limited, a choice of sizes can be supplied pre-commissioned in a prefabricated, prewired pod, ready for a single lift to the rooftop.

In terms of day to day living, overheating has become a common feature of multi-occupancy buildings. Centralised heat generation systems significantly increase temperature build-up in communal areas, a factor which, ironically, has been made worse by improved energy efficiency and air tightness standards. The secondary use of a mechanical smoke ventilation system is, therefore, becoming more common, as it provides an effective means of reducing temperatures deep within a building. It does this by using the smoke shaft as a cooling chamber so that, when combined with low-level inlet air, it provides negative pressure to draw air up through the building.