What Every Fire-Fighter Should Know
A Series of Articles Covering Every Phase of Fire Fighting
(Continued from page 321)
Probably no subject has received more deserved attention in recent years by those who give careful thought to fire fighting than the subject of ventilation.
It has been practiced to a certain extent by most fire departments, but the exact status of it was not determined until very recently. In the New York fire department, for instance, the practice began gaining impetus years ago, and was assuming some tangible form when an order was issued in the department that unnecessary breaking of glass at fires would not be tolerated. This order, insignificant and innocent as it may appear, meant the undoing of all that had been accomplished in the way of ventilating. For fear of violating the order, the men went to almost ridiculous extremes to avoid breaking glass, even refraining from breaking skylights and windows so necessary in ventilating.
The officers, too, hesitated to violate the order, no matter how apparent it was that good would come from such violation. In late years, however, the subject was ever, was regenerated until at present it stands out as being one of the most essential steps to take in fire fighting.
Before entering on the subject of ventilation, a word relative to the fundamental principle thereof may not be out of place. Why do flames, hot gases and smoke rise? They rise for the same reason that a cork will rise when released at the bottom of a tub of water. When a body is immersed in a fluid, that body is buoyed up by a force equal to the weight of fluid displaced by the body. If a bag full of gas displaced one pound of air in the atmosphere, that is, occupied the space that a pound of air would, the force tending to raise the bag would be one pound. If the bag rose, it would show that the bag, plus the gas therein, must weigh less than one pound. If the bag and the gas weighed more than one pound, it would not rise, for the force tending to raise it is only one pound. Oil floats on water, for if it were immersed it would displace a weight of water greater than its own weight; a balloon inflated with light gases floats in the air because it weighs less than the air displaced, and hot gases and warm air rise because on heating they expand and displace a volume of the surrounding cool air greater than their own weight and therefore must “come to the top.”
As a concrete example, 200 cubic feet of air at 36 degrees F. will expand to occupy a space of 300 cubic feet at 300 degrees F., or the volume increases 50 per cent, by heating 264 degrees F. And the weight of the air per cubic foot must then decrease one-third by heating it through this range. Thus if 200 pounds of air were heated 264 degrees, it would occupy the same space that 300 pounds of unheated air would. In other words it would displace 300 pounds of unheated air.
The overbalancing force which causes this heated air to rise would then be 300 – 200 = 100 pounds. It will be plainly seen that where air is heated to over 1,000 degrees F. at fires, it will rise very rapidly, in fact, rapidly enough to carry embers and pieces of charred wood to considerable heights. This is one reason why it requires quite a solid stream of water to do effective work at a fire, for if the stream is in the form of a spray when it passes over the wall of a building into the seething flames inside, the velocity of the rising gases and heated air is sufficient to keep the water from even reaching the burning material itself. The practice of ventilation is based on this principle. Hot air, gases and smoke (excepting a few heavy gases such as chlorine, etc.), tend to rise in a building on fire.
If the fire is in the basement (Fig. 38) and the smoke and gases have access to the elevator shaft, they immediately rise. This fact is clearly demonstrated by an experiment described later. They rise to the roof, and if they cannot escape, they begin piling up and backing down in the shaft and onto the upper floors. The hot gases and smoke below push upward and facilitate the spreading of the smoke into the floors above. In time, these gases and smoke will have hacked far enough down the shaft to enter the first floor. Their temperature at this point is likely to be sufficient to ignite partitions and materials on the first floor. Once this occurs, the second, third and following floors will in turn be ignited.
The object of ventilation is twofold: First, to draw the hot gases straight up the elevator or other shafts and through the roof to the atmosphere, thereby preventing the mushrooming of the fire on the various floors; second, to draw away the heavy smoke and gases which may have backed up to the very seat of the fire, so that the men with lines can do effective work and at close range. In order to firmly establish the judiciousness of the practice and settle permanently any question which may arise in the minds of its members, the New York Fire College erected at its drill headquarters a miniature facsimile of an office building but built dual. The structure, a floor plan of which is shown in Fig. 39, was built of concrete and is fire stories high, each story being about two feet in height. A thick concrete wall separates the structure into two sections, each having an independent shaft or flue from the bottom through to the top. Each of the floors is in direct communication with its shaft. In the test, excelsior was placed in equal quantities and similarly stacked on each floor in both sections, as indicated in Fig. 40. The shaft on one side was closed at the top, while the other remained open. Fire was started at the base of each shaft at the same moment and so regulated that each fire made equal initial progress. Fig. 41 illustrates the building just before the fires were lighted.
The results of the test, and which have been the same in the numerous instances it has been carried out, seem to show beyond doubt the wisdom of properly ventilating. Fire shot straight up the shaft where ventilation was provided, Fig. 40, and did not touch the excelsior on any above the ground floor. In the closed shaft, however, the smoke and flames were seen to rise to the top of the shaft and the smoke and hot gases pile up. It was not long until they backed down far enough to ignite the excelsior on the top floor. A few moments later the excelsior on the third floor, and then on the second, was ablaze. Fig. 42 clearly shows the fire backing out into the floors of the unventilated section. In the meantime the smoke, flame and hot gases in the ventilated section passed on up the shaft, not igniting the excelsior on any of the floors. It may be mentioned here, that in order to make the material more sensitive to ignition, matches had been mixed with the excelsior just before the fires had been lit at the bottom. As soon as the lid at the top of the open shaft was placed on it, the performance of the closed shaft was repeated, each floor in turn taking the fire. Removing the lid had a very noticeable effect on the fire, for as soon as it was taken off the flames and smoke which were being forced out of the front openings on the different floors were suddenly sucked in.
This experiment is given to establish the principle. Its application to fire fighting is given in following paragraphs. It must be remembered, however, that the theory of ventilation is not at all infallible, for there are proper and wrong times for its use. Judgment must be used.
Operation of Venting
The operation of venting a structure involved with fire is of the utmost importance in a fire department operation, for the prompt “opening up” of this or that particular part of a structure, as conditions call for, liberates the smoke, heat and gases of combustion, which permits of the quicker extinguishment of the fire and also prevents what is called “mushrooming” on upper floors.
Where a fire is extending through a vertical shaft, let it be a stairwell, elevator, light, air, dumbwaiter or vent shaft, it is absolutely necessary that prompt action be taken by the first officer to arrive, irrespective of whether it is an engine or hook and ladder company that he is in command of. You, no doubt, have seen engine companies at a fire time and time again and the officer in charge would not take any action, he having the wrong idea that this work was solely the work of a truck company.
It is not claimed that the one man that may be sent to a roof by an engine company will be able to do all the opening up that is necessary on all occasions, but in nearly every instance such preliminary work as he is able to carry out is of untold value to the company in further operations within the structure. Quick action on his part the keynote, and it would be his duty to remove covering over all vertical shafts, open bulkheads and dumbwaiter doors and breaking all glass enclosures over same, where this is actually necessary. Each officer should give advance instructions to each and every member of his command regarding this particular part of our duty.
In opening up any part of a structure below or on a level with the fire, exercise caution and common sense, in that your work does not create a draft unless you have a charged line on the spot to attack the fire.
If you are about to open up a roof, be sure to note surrounding conditions, as to whether such opening will jeopardize surrounding structures through side window exposure. Where such a hazard exists it would be your duty to notify the officer in charge of the fire or the nearest subordinate chief officer available as to the conditions, and to receive further instructions. In cases where the building involved with fire has a wide frontage an opening might be made in the roof, on that side of the building furthest away from the side exposure. In cellar or sub-cellar fires on your arrival it is well to open up such doors or windows (front and rear) on first floor, as it is possible to do so. It may be that if you wait too long you will be unable to do so. In addition it would be good practice to open up the top of elevator or other vertical shaft connecting with such cellar or sub-cellar. How do you know whether the cellar or sub-cellar doors leading to elevator shafts were closed by the occupant or employers when they left the premises? How do you know whether the fire is traveling up the shaft or not? A number of cases can be cited where the circumstances just described were an actual occurrence, and where a prompt opening up of the top of elevator shaft would have avoided a spread of the fire to upper floors of the structure.
When opening the top of any vertical shaft at roof, it is well for all officers to see whether there is any further interior construction that might act as an obstruction to the venting of the structure; and, when making an opening in a roof, exercise the precautions necessary as to a board, tin or lath and plaster ceiling under roof, or a floor for that matter to obtain a clear vent. Don’t place any great value on the little 2 1/2-inch x 3-inch scuttle as a means of venting any structure involved with fire. Think and act quickly as to whether a larger opening in roof is required, and enlarge such opening at that or such other point as your judgment and experience dictate.
Ladder may be Used in Opening Up
The suggestion is offered that in the case of serious cellar fires a beam ladder of sufficient length be used as a ram for opening all such doors, which may be opened more quickly and at the same time lessening the danger of men being caught by a back draft. Frequently the area under deadlights is cut off from cellar by glazed sash, which should be removed by use of a ladder or one of the longer hooks after the deadlights at sidewalk are broken. Under no circumstances, unless by special direction of a chief officer, should deadlights be broken or removed directly in front of the entrance to first floor.
Iron shutters on a building should be opened by commencing at the uppermost floor (if conditions call for it) opening first the shutter most remote from the means by which you descend.
In opening a roof, so regulate the work that you will have the wind at your back and give consideration to a ready means of escape in case the necessity should arise.
Where there are no fire escapes on the front of a building, and the opening up of one or more windows is required, the extension or portable ladders may be used within the limits of the reach of each, and a ladder properly handled will bring quicker results than a man with a hook carrying on the same operations.
In buildings of any type, where windows are beyond the reach of an extension ladder and it is found necessary to break glass in such windows for the purpose of venting the floor, a scaling ladder properly handled by two men will fill the bill. Scaling ladder should be put, butt downward through window of floor, below that upon which it is proposed to operate, these ladders should be raised up, until it is in front of window that is to be broken with end of hook pointing toward the roadway; then the men grasping the beam of ladder should give it a quick twist so that the hook of ladder will strike a sharp blow on the window glass.
Where it is possible to do so, see that window sashes are pulled up or down as required, but if it is necessary to break the glass, avoid hrraking the sash if possible
(To be continued)