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Fire Behavior
I'm confused, maybe somebody can help explain this. When I took my level 1 (recently) we were told roof ventilation would not increase fire intensity and on an interior entry sounding the floor while searching is what you need to do while searching in zero vis. Was just reading testing conclusions from UL and they say none of this stuff is accurate and in some cases more dangerous then helpful. While reading there were other techniques taught in level 1 that are contradicted and possibly dangerous or wrong.
steve
Replies to This Discussion
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Permalink Reply by captnjak on
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I am not aware of UL commenting on sounding of floors. Of course that doesn't mean they haven't. Maybe others on here are more familiar with that. The big advantage to sounding the floor, IMO, is in recognizing a change to the sound. It could indicate a weak floor. There are other things that can affect the sound so it is more of an indication of possible problem than definite problem.
Ul is not trying to tell us how to fight fires. They are giving us information to use in fighting them more effectively and safely. Opening a roof is a method of relieving a building of smoke, heat and gases which alleviates interior conditions for occupants and firefighters. When the opening is made, a draft is created. Fresh air moves in from lower levels to replace the air vented out the top. This fresh air mixes with the already present heat and fire gases, resulting in the fire "lighting up". Fire will increase in intensity and size if it is not immediately cooled by water. Opening the roof in and of itself is not an extinguishment tactic. The heat will not all rise up out of the building thereby letting the fire go out. Opening the roof is a tactic to use in conjunction with extinguishment.
UL has also shown that an opening that is not of sufficient size will not be effective. A small hole cut directly over the fire with the ceiling pushed down may not create a sufficient draft. Fire may vent out the roof and still continue to vent horizontally out windows and doors. Firefighters operating in such structures without protection of a hand line could be fooled into thinking that the roof opening will make conditions tenable while they await a hose line. The entire area then could light up. This situation is untenable for firefighters even in full PPE. Immediate water application or removal from area would be the only thing that could save them. By immediate, we're talking seconds not minutes.
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Permalink Reply by Norm Tindell on
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Short answer following up on what captnjak said: Timing and coordination are critical when ventilating. In other words, if you vent too soon you create more problems for the guys down below than you alleviate.
When it comes to sounding I can't imagine that not being a good idea. Sound everything you are stepping onto and walking on when in a potentially hazardous environment.
Always consult your training officer on any strategy and tactics questions.
Stay safe.
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Permalink Reply by steve hutchinson on
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That helps me understand better when to ventilate. Can ventilation in the wrong area draw the fire to various areas of a structure intensifying the fire propagation?
steve
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Permalink Reply by FETC on
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Steve,
Great question and you are not alone in your confusion. Unfortunately your fire school curriculum is based off of a true (CO) carbon monoxide only based fire behavior model. With flashover based from 1100 F. In the old days, you could vent a window or put a hole in the roof and watch the smoke billow out of the ventilation port and it often would not light up. The reason is the unburn't particles contained in the smoke, (soot) and (CO) needed to be at or above 1100 F for that fuel to flash when it met the outside ambient air that contained Oxygen. Smoke is contained in an environment, it is lacking O2. The box is rich. That side of the fire triangle is missing to have spontaneous fire. What science is telling us now is things happen at different times and temperatures because the furnishings (fuel load) is heavily based from hydrocarbon and synthetic based materials. That said todays fires are not based from a past CO fire behavior. It has been proven that Acrolein, Toluene, Benzene, CO and Hydrogen Cyanide is found in todays smoke. Of those gases, Acrolein has a flashpoint in the 400F range. Now a days when you vent a window or leave the entry door open, the smoke that comes out of that port will touch off and you now have fire in front of you and fire behind you.
Therefore the fuels are causing rapid fire increases, interpreted as flashover. Not a day goes by without an internet report of firefighters suffering a flashover. Knowing that if they were truly in a flashover, many of these brothers would not have survived. Did the room flash, yes, was it at old flashover temperatures, No. If it was at the 1100F for which the entire room flashed, it would produce dead firemen.
Curriculums are still based off of 1950-1960 carbon monoxide based fire behavior. Keep reading and take nothing as exact science. The world contains 84,000 chemicals and every fire you go into is now a toxic soup of hazmat in motion. Textbooks today are behind the times because it takes years of visiting committees to work through the science and adjust the curriculum produced in textbooks.
We teach classes on the new fire behavior science and it is an eye opener for everyone who sits in. Stay safe.
Bill
FETC Services
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You are right they never talked about old versus new flash points in school. I love this site it is full of information that you can't get from a textbook. It's good for us younger guys to be able to ask the veterans what really happens when the SHTF. thanks.
steve
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Absolutely. Any opening we make is going to affect fire conditions and therefore fire behavior. Sometimes it is more noticeable than others. Size and location of openings, amount of fire and size of building will all contribute. Amount of water and when it is applied during the ventilation process will determine if things get better and how quickly it gets better.
It all comes down to movement of air masses. The interior air is hot and loaded with suspended fire gases (fuel). For it to get out of building, new air needs to come in and replace it. If and when the two mix, fire is likely to light up and increase in size and intensity if hoseline is not there to cool the area. Either way there is a route that the hot gases take to get out of the building or area. This is the "flow path". Get used to hearing that term. It's relatively new as far as widespread use in the fire service . We need to understand it to function in the most effective and safest manner.
We used to talk about horizontal vs. vertical ventilation and venting for fire vs. venting for life. Now we talk more about controlled vs. uncontrolled ventilation. Timing is everything. Ventilation too far in advance of water application is not a good tactic. It will worsen conditions as opposed to improving conditions. If an interior search has begun, we could be putting the search team in an untenable position.
Keep in mind that opening a door to enter for search is ventilation too.
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backdraft scared as hell of it. Some very interesting points you make definitely better then how we learned in school.
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They seem to have changed the terminology on us. It used to be that when an area contained high heat and airborne unburned fuel, then lit up with the introduction of oxygen we would call that a backdraft. Now they're calling it a "ventilation induced flashover". I suppose that is a more accurate and descriptive term for what is happening. As long as we all understand what is happening, and why it happens, I don't much care what it's called.
I don't think we should get too hung up on the specific gases involved and the temperatures at which they light up. None of these gases exist in a vacuum. They will all be present in the environment of our typical contents fire. We know that temperatures following a ventilation induced flashover will very rapidly rise well above the 1100 degree mark if not immediately cooled by a hoseline. Temperatures are now being found to be as high as 1800 degrees or more post flashover. We know such an atmosphere is untenable for firefighters.
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What is to hot for being in the hot zone, what is your best indicator to tell you it's too hot get out? In school they took us to the burn house at the college and he stoked up a good fire. Instructor was there showing us how to knock it down, the heat was unbelievable and worse was the steam that came back at us when we gave it a direct shot at the base. Some of the guys left their dog tags on their helmets and they melted from the heat. I now respect fire.
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The rule we go by is:
"If you feel heat through ANY of your gear get out" unless the area can be immediately cooled by a hoseline.
I can't help but to wonder how hot it was to melt your dog tags (and what they're made of). I don't know what college you were at and I don't want to know. I do not want to bash anybody, but the instructor should only make the room as hot as it needs to be in order to teach the lesson. IMO, some instructors go well overboard for no real reason. They forget that they're supposed to be TEACHING you, not impressing (or scaring) you. If the goal is to teach a group how to stretch, operate and advance a hoseline to extinguish fire, then how hot does it need to be? Why go to 1200 or more degrees when 600 degrees might serve the purpose. I'm sure a lot of training injuries could be avoided this way.
Don't compare what happens in these burn rooms to real fire situations. Way too many variables.
I'm glad you respect fire; you definitely should. Those who don't put themselves in a bad position. Anyone who does not respect fire has a lot to learn about fire.
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Permalink Reply by 55 TRUCK on
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You are right Cap. I am a flashover instructor. During our instructor course they would get it hotter than they would with recruits. All of us has 10+ yrs on in the busiest companies in the city.
We would never do that to recruits or anyone else we were teaching. (Well we might heat it up for our FDNY brothers)
I also feel that many training accidents can be attributed to a lack of experience on the instructors part. I am talking about real world experience. They try to show there knowledge by impressing green recruits. The out come is that the recruits are too scared to listen clearly therefore the lesson falls on adrenalin deaf ears. The other thing is that the recruits/recruit are injured or worse.
All because a person who really doesn't understand the dangers of fire is teaching a class. Now I know not every department can get the number of fires that. Indianapolis,New York,Detroit,East St.Louse, Chicago,D.C. etc. get. They can put the safety of the firefighters they are charged with teaching first.
The other fact that adds to this is this simple fact.
Manpower. Most small Vol., Part paid, small paid depts. Are short handed so there instructors end up being the ff with the most certs or the one willing to take all the classes. They may be very young with little to no real experience.
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