The project that we have recently concluded for the Swedish Fire Research Board shows that it is not possible to draw any general conclusion as to whether fire gases should be automatically ventilated from buildings fitted with sprinklers or not. The question needs to be decided on a case by case basis. However, some main points are summarised below.
Manuarlly opened fire ventilators
Only manually opened fire ventilators are recommended for use in sprinkled premises having only roof sprinklers and with a risk of very rapid fire growth, such as stores with high fire loads and high racks of products or goods. This is particularly important when the sprinklers have been designed merely to reduce the fire, e.g. ESFR-sprinklers. In principle, the ESFR-sprinkler regulations do not allow automatic fire ventilators to be used in combination with these sprinklers.
Automatic opening mechanisms
Automatic opening mechanisms, such as fusible links, can be used in industrial buildings or workshop premises with sprinklers where there are no high stacks of goods or goods presenting a high risk class. Nor is there anything in the literature that warns against the use of group activation of fire ventilators in this type of building by means of a signals from smoke detectors or flow switches.
In buildings where fire protection systems are designed not only to protect property but also to give priority to the safety of occupants, such as shopping centres, the use of faster opening mechanisms, such as smoke detectors, should be considered in order to facilitate evacuation.
Trials show that the area of fire gas ventilators in sprinkled premises is of less importance than it is in premises not having sprinklers. This means that the ventilator area can be reduced in sprinkled buildings, with the amount being decided from case to case.
Experience from real fires
Reported experience from real fires show that fire gas ventilation works more effectively as the size of the sprinkled fire, when the fire services arrive, increases. There are many cases where fire gas ventilation has assisted the work of the fire services when tackling with sprinkled fires. On the other hand, the literature does not describe any concrete cases in which the sprinklers have lost control of the fire due to the opening of fire gas ventilators. It therefore seems likely that much of the discussion and debate concerning the use of fire gas ventilators in sprinkled buildings is more an academic than a practical problem.
It should also be noted that there are no documented cases of fire gas ventilation having been decisive in ensuring the safety of persons evacuating from sprinkled fires.
The discussions concerning coordination of sprinklers and fire gas ventilation continue, both in the USA and in Europe. There are two strong driving forces behind this. For the first, it is claimed that earlier trials have not provided all the necessary answers, while secondly (at least in the USA) there are those who claim that fire fighting strategies should be changed, with fire gas ventilation being initiated at an early stage of the fire. This is a very interesting suggestion, which naturally helps to reduce consequential damage in the building, as early fire gas ventilation can reduce smoke damage.
The results of this work are published in SP Report 2001:17. For more information contact Haukur Ingason or Magnus Arvidson.