Tony Engdahl: Tactical Use of Positive-Pressure Ventilation and Small Water Droplets

BY Tony Engdahl

This article discusses positive-pressure ventilation (PPV) use in Gothenburg, water use and our extinguishment technique, and why ventilation and water go hand in hand. Let’s start with ventilation.  

(1) (Photos courtesy of author.)

Ventilation is not harmless. If you don’t have coordination and your group doesn’t have an understanding of what everyone has to do and in what order, it can go bad.

A Swedish fan (24 inch) can build up a pressure for 400Pa (pascal) [2.8 pounds per square inch (psi)] in closed area and in the fire room.  If there is any opening, it can only be 10-20Pa (0.014psi). But if the fire room is closed, the pressure can be as high as 1,000 – 2000Pa. So if we are going to use a fan, we must have openings. And when we work with ventilation, we always also include water (nozzle technique). The most important parameter when using PPV is that you have air outlets and that the outlets are in contact with the fire room or as close as possible. No outlet = no fan (except for pressurization) is a simple thing to remember. From the beginning, we used ventilation for a safe evacuation. We still do that, but we also use it for our firefighters’ safety and because the combustion gas, heat, and water steam will be expelled from the building and the firefighter can extinguish the fire much faster in a much safer way; it also will bring fresh air to the victim faster.

But, there is also danger. Never use PPV when you see the signs of a backdraft or if you have not located the fire or have many fires in different places. In those cases, we use natural vent. The question generally is not, Would I ventilate? It should be, When will the ventilation start? If it can be vented, we will vent it. Fire gas is very toxic because it includes deadly levels of carbon monoxide; additionally, there is a high temperature (around 600˚C-800˚c during a fully developed fire. Combustion gas is 90%-95% hot air, and it will behave like that.

Before starting any fire ventilation procedure, be well aware of what you are about to achieve with it, simply because you have to do other things as well. If you do it right, good things will happen; if you do it wrong bad things will happen. Everyone on the team must understand why and how to use ventilation. It’s about tactic, construction, fire behavior, equipment, extinguishment.

How far should you position the fan? It depends on the size (diameter) of the fan and the type of fan. Test them to see which is best. You also have to think about the air cone and the ejector ability, which are different for each fan. Sometimes you will need pressure; other times, you will need flow, depending on the tactic. So just to make it easy, if you have 1:1 same size for supply air as for exhaust air, the ventilation will always be okay. However, when you would like to have a big flow, you will need to open the air exhaust more, say 1:2 or sometimes 1:3. Table 1 shows the difference.

Table 1. Effects of Increasing Air Exhaust Flow

Supply air

1m2

1m2

1m2

Exhaust air

1m2

2m2

3m2

Effect

70%

90%

95%

The air exhaust should never be bigger than 8 m2; some opening sizes might cause wind to interfere with the objective of ventilation. Ventilation must be done at the right time, in the right way, and in the right place, and it must be coordinated with other measures. Always have a water source prepared.

Swedish Way

So what do we mean when we say “The Swedish Way?” The thing we do differently is our extinguishment technique. We call it “up-down” in normal areas and “laying eight” in large areas. The farther a drop of water will stay in the smoke, the better it will cool down. We talk about drop size but also about the speed of water and when to use low pressure and high pressure. The major advantages of fine water are its ability to absorb heat radiation from a fire and, of course, the ability of smaller drops to stay airborne longer than larger ones. But, sometime you need larger drops. It all depends on the situation.

Firefighters must always remember the following:

• Keep a low position.

• Don’t lose eye contact with your partner.

• Read the fire’s behavior

• Think “Safety.”

• Retreat at danger.

• Use the nozzle in the best possible way. Your fog nozzle might be your lifeline.

Train and train again, and have understanding and a plan what you will do with the water.

BIO

Tony Engdahl has been working in the fire brigade since 1986, the first 13 years as a fire and an ambulance responder. As an officer, in 1999, I took a position in the Swedish government school, where I worked for six years, mostly with fire officer education. I then was a fire captain in the Gothenburg fire brigade for eight years. I now work with the Swedish Rescue Training Centre), predominantly with fire and hazmat.

 

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