Sprinklers vs smoke ventilation

By Ron Burns

It would be fair to assume that the debate over sprinkler systems and smoke ventilation systems has been taking place for years, with little or no progress being made in terms of concluding which one is preferable.

smoke001Should the building be fitted with a sprinkler system without the installation of a ventilation system, the threat of asphyxiation increases.
Image credit: realtor.com

Searching the Internet seldom leads to clarification, with many articles written by leading personalities and scholars, each fighting for their moment of glory. The facts are limited, the assumptions seldom backed by proven test results, and nothing new to add. Why invest the time in writing the article?

Debate is good; debate encourages people to relook at opinions they have formed. The difficulty is to explore these opinions afresh with an open mind and perhaps learn something new. I was searching for a good analogy and thought that food would be a great go-to place to find one. I thought that comparing sprinklers and smoke ventilation would be like comparing spinach and feta. I pondered over the flavours racing across my palate and the enjoyment I would receive; so, the more I thought about it, the less I fancied the analogy. I think it is best if I settle for gin and tonic; I make no attempt to come to any conclusion as to the nutritional or flavour benefits. Instead, I think more of the morning after, the headache that will be the prevailing, and the lasting consequence of venturing into this topic.

In the event of a fire, both sprinkler systems and smoke ventilators have an important role to play in protecting life and property.

To place myself in this debate, it is important to note that for the past 18 years, I have earned an income from smoke ventilation. Perhaps my bias may be a little towards venting; however, I believe objectivity can be achieved.

In principle, the fact that sprinklers are designed to control fire and smoke ventilators to control smoke would suggest that they are a perfect combination. For years there have been an ongoing controversy regarding the interaction of sprinklers and smoke ventilators, suggesting that combining them could result in neither one of them operating to its full potential. It amazes me how facts are simply thrown into conversations to prove points; these facts carrying very little substantive research or proven case studies. In my opinion, a building that has not been fitted with a sprinkler system is destined to burn to the ground — a South African perspective. We, as South Africans, have limited resources and should a fire erupt in a building, it is unlikely for the fire to be extinguished by a member of the public. The fire services are under extreme pressure with limited resources. Being able to attend to the fire early enough to extinguish the fire is not guaranteed. The installation of a sprinkler system, which is adequately maintained, provides initial fire extinguishing opportunity. If I was personally developing a building, I would definitely install an automatic sprinkler system to protect my investment, the building.

There are two main arguments against the combined use of sprinklers and smoke ventilators:

  1. The removal of heat and smoke by ventilators could delay the operation of sprinkler heads.
  2. The ventilation system could allow the fire to burn more fiercely by maintaining the oxygen content of the building.

These two statements are contradictory; at best, the removal of the smoke and heat by the ventilators in point 1 facilitates the heat generation of the fire. This produces a clean-burning fire, less smoke, and higher heat levels, which should activate the sprinklers quicker. Once the sprinkler system is activated, the scenario changes: steam and cooling occur immediately and the controlling of the fire begins. Every smoke ventilation designer considers the effect of sprinkler cooling in their smoke ventilation calculation. With regard to the introduction of fresh air into the fire, this is governed in the design principle for providing ventilation in such a manner that the introduction of fresh air does not fan the fire. The design intention is to provide sufficient fresh air to maintain the chemistry of combustion.

I would suggest that sprinklers are designed to control fire and smoke ventilators to control smoke.

The largest loss of life in a building occurs through asphyxiation. In an unvented building, smoke logging occurs rapidly, posing immediate risk to life. Should the building be fitted with a sprinkler system without the installation of a ventilation system, the threat of asphyxiation increases. The smoke temperature cools, resulting in a loss of buoyancy as a result of the sprinklers cooling the smoke. The smoke descends to low level, encroaching on the evacuation space. The cool smoke is then fed back into the seat of the fire, resulting in an incomplete process of combustion, potentially facilitating a backdraught scenario should the fire overpower the sprinkler system. This poses a threat to the fire department when attending to the fire. These threats could be mitigated with the installation of a smoke ventilation system. Although discussing the cooling effect of the sprinklers on the smoke in the negative aspect, it is critical to the protection of the building. The sprinklers need to cool the smoke temperature to prevent excessive loss in the fire. The challenge is to remove the smoke as efficiently as possible.

Another negative consideration of an unvented building is the build-up of heat at roof level. With no ventilation, the heat is trapped and cannot escape. This would suggest that the temperature is likely to set off additional sprinklers as the temperature at high level increases. A well-vented building would definitely release the heat at high level, introducing oxygen-enriched fresh air at low level and facilitating the operation of the correct sprinklers over the seat of the fire.

In the event of a fire, both sprinkler systems and smoke ventilators have an important role to play in protecting life and property.

smoke002Sprinkler and smoke ventilation systems have different and independent functions with neither being more important than the other.
Image credit: dutcotennant

Sprinkler and smoke ventilation systems have different and independent functions with neither being more important than the other. This is the point, in my opinion, where the discussion goes poorly. These systems work together, their roles complementary. There is never a case where one system is better than the other; omitting one of these systems offers no benefit other than a financial saving during the construction phase of the building; however, the long-term consequences of having a building where one of these systems has not been installed places a risk on the occupants and the goods for the life of the building — a point seldom considered.

I would suggest that sprinklers are designed to control fire and smoke ventilators to control smoke. This is indeed a perfect combination. With the provision that both systems have been designed to the current set of internationally accepted standards and that they are installed by competent and approved installers. There should be no concerns that the interaction between the two systems — sprinklers and smoke ventilators — will limit either system from operating to its full potential.


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