Proper use of mechanical ventilation aids
FIREMEN know that the removal of smoke, hot air and dangerous gases from a building will enable them to locate quickly the seat of a fire and advance hose lines to attack the flames. They also know that ventilation will help save lives, prevent so-called back drafts, reduce water and smoke damage and prevent unnecessary fire spread by directing the products of combustion through a desired channel to the outside atmosphere.
Ventilation in fire fighting terms usually refers to natural vertical ventilation. No one should overlook its advantages, especially in large fires or in situations where drawing the smoke up will accomplish the intended purpose. Horizontal or lateral ventilation is frequently employed for fire fighting purposes where it is necessary to clear the atmosphere of a single floor or a room and it is desired that little of the smoke travel upward.
One problem associated with natural horizontal ventilation is its relative slowness in clearing the atmosphere when compared with vertical ventilation. By employing some mechanical means of assistance the process can be speeded and the smoke can be channeled as required by the conditions.
To properly perform mechanically assisted horizontal ventilation, firemen should first know the basic principles of natural ventilation as much of that knowledge will be necessary to do a more efficient job. In natural ventilation the fireman is dependent on the forces of nature, but in mechanical ventilation the fireman creates the desired circulation by his knowledge, equipment, and actions. Both types of ventilation have many advantages, but if improperly performed or without regard for existing conditions, both can have adverse results. Successful mechanical horizontal ventilation is largely dependent on seven rules, as follows:
- Place an exhausting smoke ejector in an outside opening nearest to the source of the smoke.
- Place the smoke ejector as high as possible in the opening.
- Use prevailing winds as much as possible.
- Prevent the smoke ejector from “churning air.”
- Control the flow of incoming air.
- Prevent interference with airflow —both into and out of the ejector.
This should be the first smoke ejector placed unless some other action is dictated by the emergency. The initial problem is to get the smoke out and the shortest path is usually the best. Many times smoke ejectors can be positioned to push or blow the products of combustion to the exhausting smoke ejectors working in the outside openings and in this manner create advantageous circulation. The basic idea is to develop an artificial circulation in the same direction as the natural wind if possible.
Heat, congested fumes, and smoke are at or near the ceiling in larger amounts than in other portions of the room at the start of the fire attack. That is the place where they should be removed first to decrease the amount of heat and products of combustion and gain visibility. The cool fresh air will come in by itself if heat and smoke are removed.
Know the direction of wind and use it to push or blow the products of combustion to the smoke ejector. Of all the fire fighting aids, the direction of the wind is too often not known by the firemen inside the building.
If it is necessary to use a smoke ejector into the wind, cock it in such a way that the products of combustion will be expelled and not return into the building through other openings nearby.
Air will follow the path of the least resistance and will recirculate both around the sides of the smoke ejector and “in and out” of openings close to it causing a “churning action.” When this is done, efficiency is lost.
To increase the desired circulation, close openings near the smoke ejector and cover the space around it as much as possible. Ideally, if you could cover all of the space in the opening, except that of the smoke ejector, it would give you the best results.
Set up the draft path desired and keep this circulation in as straight a line as possible. Every comer you go around will cause more turbulence and inefficiency. Avoid opening windows or doors near the exhausting smoke ejector, unless this definitely increases the circulation.
Over 50 per cent of the effectiveness is lost blowing through a common window screen. Do not blow into a wall or door close to the smoke ejector as this will cause inefficiency.
As with natural ventilation, have a charged hose line at hand when ready to place smoke ejectors, but use them soon enough to prevent damage from smoke stain and smoke odor.
Remember, visibility is gained quicker and locating the fire is made easier by having smoke ejectors ready when hose lines are in position at smoky fires.
As with any type of ventilation, these rules are a unit and should be intelligently applied. One is no more important than another. Each, in a given situation, could be the most important. Too, they are basic rules and good smoke ejection requires the scientific application of good firemanship.
Whenever natural ventilation is even partially unsatisfactory, mechanical ventilation should be used. Conditions where people are sick, injured, mentally deficient, or confined makes mechanical ventilation a very desired fire fighting procedure. Pulling the products of combustion away from the occupants and their means of egress for a period long enough for their escape or their rescue by firemen, is desired and may be possible if the equipment is properly used.
Use as a blower
Smoke ejectors are not limited to exhausting the initial heat and smoke from a building. After initial ejection has started and the smoke has become thin and less buoyant, much more can be eliminated more quickly if proper blowing action is started.
- Have an exhausting smoke ejector working on the lee side of the room or building unless this will spread the smoke to uncontaminated portions of the building or otherwise expose other property to damage.
- Place a blowing smoke ejector at an opening where it will admit the fresh, clean air. Usually this is the low part of the opening. The floor in a doorway near an outside opening on the windward side is often very effective. Do not place the ejector directly below an opening against a wall as this will decrease the desired blowing action. Place the blowing ejector about 8 feet or more from the outside opening.
Clear the room or building from the windward side toward the exhausting smoke ejector by moving blowing smoke ejectors toward the exhausting ejector. Keep circulation line as straight as possible.
Place blowing smoke ejectors at the bottom of closets and small rooms to blow fresh, clean air in and force smoke and odors out the top of the door opening.
In residences and smaller type buildings, apply a number of blowing smoke ejectors in the lowest floor or basement operating from outside openings or suitable windows. Close all openings on this lower floor and cover the space around the smoke ejectors to create a “pressure-type” circulation to push or force smoke and odors out of air or heating ducts and other concealed spaces. It is advisable to have an exhausting smoke ejector in the floor above to remove the disturbed smoke and odor to the outside atmosphere.
Place a blower in or near an outside opening directed over all fabrics or other material which may retain smoke to remove as much of the odor from such material as is possible. After this action a smoke neutralizer or deodorant may be used to good effect.
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Prevent curtains, drapes, etc., from covering or entering intake of smoke ejector or covering its guard. Supervise traffic in the area of a smoke ejector on a floor, especially where there are women with dresses. The suction action of the smoke ejector can draw a dress into the unit and do damage. Keep children away from any operating smoke ejector.
Never pick up any smoke ejector by anything but its handles.
Do not operate smoke ejectors too long in severe cold weather, especially, if the fire has affected the heating system. The increased air circulation could cause water pipes to freeze and occupants to become cold or lead to their becoming sick. Remember, the very young and elderly are susceptible to cold.
Prevent blowing papers, loose material, debris, or dirt around which could add to the damage or inconvenience the occupants.
Be careful that doors and other obstructions in the air path do close and shut off air circulation.