Positive Pressure Ventilation,
applied as a Fire Attack and Rescue Tool.
THE SITUATION
Picture yourself arriving at the scene of an early morning residential fire with reported entrapment. Your size up reveals that you have a 3 bedroom, single story dwelling, 25% involved, with heavy smoke showing. Conditions are deteriorating, with the smoke banking towards the floor, and heat levels becoming dangerously high, further endangering any possible trapped victims.
Your plan is to initiate an aggressive offensive attack, with a simultaneous search and rescue effort. Strategy calls for the attack team to stretch a 1 3/4" attack line, vent for fire, locate and isolate the seat of the fire, and extinguish the fire. The search teams will utilize the vent-enter-search approach, under the protection of the attack team.
THE PROBLEM
There is little to no visibility, making the search effort painfully slow. Locating the seat of the fire is extremely difficult, the attack team being punished by advancing into the high heat conditions. What you need is something to increase the effectiveness of your efforts, to tip the odds in favor of the lives and property you are trying to save. The very tool that you need is already at your immediate disposal.
VENTILATION BASICS
Let's get back to the basics and examine the conditions that may be encountered by the interior teams. Smoke that has banked down to near floor level during free burning, or smoke dropping down due to cooling by fire streams or sprinkler systems, will decrease or altogether eliminate visibility. High heat from the fire itself, or from steam conversion from fire streams, may prevent effective fire location and suppression. These conditions are routinely managed by the use of ventilation.
Ventilation may be carried out by allowing combustion products to exit a structure on a horizontal or vertical plane, via existing or created openings. This method is referred to as natural ventilation.
Ventilation may also be carried out by forcing combustion products to exit on a
horizontal or vertical plane, via existing or created openings. This method is referred to as mechanical ventilation.
The mechanical ventilation is accomplished by either increasing or decreasing the atmospheric pressure within the structure. By directing a flow of air into the structure,which increases the atmospheric pressure within the structure, the gases flow to the lower pressure outside the structure, know as positive pressure ventilation.
By directing a flow of air out of the structure, which decreases the atmospheric pressure within the structure, the gases are drawn out of the structure, the higher pressure outside of the structure will force fresh air into the structure, known as negative pressure ventilation.
There are two reasons for accomplishing ventilation. The first reason is "venting for fire", which will allow firefighters to access the structure, seek out and attack the fire.
The second reason is "venting for life", or drawing the products of combustion away from the victims, while firefighters enter the area, locate, and rescue them.
Venting for fire is normally delayed until the resources are in place to attack the fire, as opposed to venting for life, which should obviously begin as soon as the life hazard is recognized. Thus, the major difference is in the time of execution.
THE SOLUTION
Smoke ejectors have long been utilized to remove smoke, heat, and toxic gases from enclosed areas after the fire has been extinguished, and increase the visibility during the overhaul phase of operations.
While this use of smoke ejectors has and will continue to be an effective tool, there is an equally effective, but seldom applied tactic, of utilizing smoke ejectors during the fire attack and rescue phase of operations.
There are a great number of people who still resist accepting or even acknowledging this tactic. This is NOT a new, untried, or extra item to be added into the many events of fireground operations. It is in fact a widely used and very effective event. And by merely adjusting the time of execution, it can make a drastic increase in the effectiveness of an aggressive offensive fire attack or rescue evolution.
THE METHOD
To use this tactic to it's fullest potential, you need only to incorporate it into your existing strategies for fire attack and search/rescue operations. This may be done as follows:
1) Natural venting for fire or life, either horizontal or vertical, is executed when the attack or search team is ready to make entry.
2) As the team enters the structure, the smoke ejector is applied to the point of entry behind the team. The smoke ejector should be placed far from the door, and in a manner to avoid obstructing the entry point, yet near enough to effectively seal off the entire entry point. This will push the products of combustion ahead of the team, and out of the structure.
THE BENEFITS
Smoke and heat will vent from the structure as it does in natural ventilation, but at a tremendously faster rate. Thus, you speed the creating of a cooler atmosphere for the attack team to operate in, thus more rapidly reducing the physical stress on the team.
The products of combustion will be removed from the vicinity of the victims faster, creating a more survivable atmosphere, and increasing their chance of survival. The visibility will also increase at a much faster rate, resulting in locating and removing the victims from harm in a shorter amount of time.
Excessive heat will be removed from the structure, possibly preventing a flashover situation. Fire streams directed to the uppers areas to further prevent flashover, which normally may invert the thermal stratification, will decrease the amount of heat descending upon the team.
By following proper existing ventilation procedures, and incorporating these steps into those procedures, you increase the effectiveness of the team and department, build more positive image of the department, and foster a better relationship with the community.
! CAUTION !
This method of ventilation in no means should override or eliminate any standing safety procedures, but should supplement those existing procedures.
This method of ventilation and should not be utilized without the use of an attack line charged and ready, or if fire conditions indicate a potential backdraft situatuion.
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