Ventilation Is Important To Use of Fog Streams
departments
The Volunteers Corner
When we think of venting a burning building, we generally think in terms of removing superheated gases to prevent the fire from mushrooming, to avoid a back draft and to facilitate the entry of fire fighters. These are not the only reasons, but they are the ones that most directly affect the fire suppression efforts.
The last reason, to facilitate the entry of fire fighters, is of particular importance and its relationship to fog streams is sometimes overlooked. When straight tips were the standard for fire attack, the solid streams provided a reach that allowed fire fighters to remain some distance from the seat of the fire—provided partitions were not in the way.
The advent of the fog nozzle has changed this. Forget the indirect attack for special fire conditions in a relatively tight building and skip the blitz attack, which again is for special fire conditions. Let’s look at the run-of-the-mill fire attack in which, day after day, we use fog streams.
Must get inside: We use fog nozzles because they do a better job for us than solid tips. Fog streams knock down fires faster than solid streams and they do less water damage. Frequently, there is little or no runoff water from fog streams. But to apply fog streams effectively, we have to get inside the building and close to the seat of the fire. Fog streams don’t have the reach of solid streams and they are more likely to be affected by thermal currents. To use fog streams most efficiently, we have to get close.
That’s where ventilation becomes a vital partner of the fog stream. Ventilation works to our advantage in two ways. First, it makes it possible for us to enter the building and to continue toward the burning room or rooms. Sometimes it is necessary to crawl on our hands and knees to advance the line to the point where it is desirable to open the nozzle, but without ventilation, even this would be impossible to the extent we desire.
Protection of men: Secondly, ventilation provides protection for the hose crew after they open the nozzle and the fog stream enters the superheated atmosphere ahead of them. As the water droplets reach this superheated atmosphere, they turn into steam at a ratio of about 1600 volumes of steam to one volume of water.
This rapid and extensive development of steam creates a situation in which the steam must move somewhere, and it will move somewhere immediately. If there is adequate ventilation beyond the fog stream or above the fire, the voluminous generation of searing steam will move to the outside of the building. The hose crew will continue to operate in relative comfort and can move forward as fire is darkened down and the fire area temperature begins to drop.
If there is no ventilation, or ventilation is inadequate, the steam will move from the fire area through the building. Now guess who is first in the line of steam movement from the fire area through the building. Without any ventilation, the hose crew will be inundated with steam and they generally will be forced to retreat. They may have to direct their fog stream overhead for a moment to obtain immediate cooling of the atmosphere around them as they retreat. Meanwhile, the fire will begin to recover its intensity.
Ventilation is not only desirable, it is vital for effective application of water fog in an interior attack on a fire.
Cellar fires: Ventilation is a tremendous problem at cellar fires and that is why we make very effort to get as much ventilation as possible at these fires. It is almost impossible to get adequate ventilation at most cellar fires because of the few available openings in most cellars.
Sometimes additional ventilation can be provided by cutting a hole in the floor near a window. This can be helpful, but it also can increase the smoke problem on the first floor. The resultant smoke damage might be excessive and you have to determine whether crews will then be able to advance lines into the cellar or whether you should skip the extra ventilation effort and go immediately to the use of cellar pipes or high expansion foam.
Cockloft fires: Another specific situation in which ventilation is vital to the successful use of fog streams is the cockloft fire. Cocklofts, most frequently 2 to 3 or 4 feet in depth, extend over stores, some houses and condominiums, and even the office areas of some industrial buildings. The stores may be small single stores, row stores (taxpayers), or supermarkets, and row houses sometimes have a common cockloft without a fire wall between the houses to cut off fire in the cockloft.
In any event, the roof must be opened over a sizable fire before the ceiling to the cockloft is pulled to put a hose stream on the fire. Without roof ventilation, the fire, hot gases and steam will envelop the hose crew as they make the attack through the pulled ceiling.
Under the worst conditions, the fire in the cockloft will reach the smoldering stage, and there will be a back draft condition in the cockloft. Without roof ventilation first, pulling the ceiling may trigger the back draft and those in the area will be the victims.
If we are going to use fog streams successfully, ventilation is a vital part of the fire fighting operation. Without ventilation, we endanger ourselves and at the same time do a poor job of attacking the fire.
