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Effective Ventilation

August 25, 2009

I spent the last part of my firefighting career in New Zealand.  Firefighters there, unlike their American counterparts, do not often employ vertical and horizontal ventilation as an offensive firefighting tactic.  In the United States, firefighters often break windows or cut holes in the roofs of burning buildings so smoke and heated gases produced by the fire can escape freely.

These tactics reduce the dangers of flashover and backdraft, which occur in the first instance when all of the available combustibles in a compartment reach their ignition temperatures at or near the same time and in the second instance when fuel-laden smoke heated beyond its ignition temperature is mixed with air in the right proportion to ignite, sometimes with explosive force.  Either of these conditions can render a building untenable for anyone left inside or anyone entering unawares.  For this reason, firefighters employ these tactics judiciously and under close supervision only after securing an adequate water supply with which to fight the fire.

Venting a building is not a panacea.  Letting smoke out also lets fresh air in, which in turn increases the burning rate of the materials already ignited.  Consequently, firefighters have to be ready and able to get to work quickly to extinguish what’s already on fire and prevent it from spreading to anything else.

Organizations, like building fires, often suffer from inadequate ventilation.  Stifling the burning rate keeps things from getting completely out of control, but that does not necessarily make the situation safer for those working in the organization nor more efficient.

In the absence of effective ventilation, New Zealand firefighters used cooling sprays of water to reduce the pent up energy near the ceiling before they entered a burning building.  This reduced the danger of flashover but not backdraft.  Moreover, it often made the job of finding and attacking the fire more difficult due to poor visibility and the added stress of heat and moisture penetrating their firefighting gear.

Like cooling the heated upper gas layer in a fire, pouring cold water on those showing initiative, even if its done indirectly, can have a chilling effect on the entire organization.  Employing such tactics may be necessary and even beneficial under certain circumstances, especially in concert with targeted measures that attack specific problems directly but should never be taken as the sole strategy for keeping things under control.

To be fair, it often makes little difference in the outcome of a fire whether firefighters use American of Kiwi tactics to attack it.  But when it does matter, the lack of openness can impede both efficiency and effectiveness, and it sometimes contributes to dangerous conditions that jeopardize safety and performance.

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