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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Operational => Topic started by: The Lawman on July 03, 2007, 10:17:42 PM
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Hi ,
I have read all I can find about backdraft and seen the demos/videos but have never yet been told exactly what to do to combat the problem. Exactly how do you safely ventilate a compartment when such conditions exist?
I'm very fortunate not to have encountered this yet operationally but who knows, it could be my next shout!
Cheers for any help....
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First thing is to make the determination that b/d conditions actually exist within the compartment. Very difficult without physically entering.
Then, to control the ventilation, you need to create openings by breaking windows, preferably at a high level. ( Manual authors - Ever tried breaking a d/g upper floor window with a ceiling hook from the ground? Thought not.) Once you have an opening for air to get in and for it to get out again, get the PPV to push it around then re-assess.
It all boils down to experience. If you aren't attending incidents where you get exposure to this sort of thing then al you have to go on is training received and doing your best to translate that into real life when it happens.
I know that there are some very experienced people out there that can provide you with some alternatives. Let's just hope they respond.
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The thinking when I was in the job was to observe the signs of the smoke behaviour at leakage paths from the fire compartment and without intoducing air to give the upper part of the room repeated blasts with a water mist/ fine spray to reduce the temperature and replace the flammable atmosphere with a steam laden one. Ventilation can then follow once the back draught risk has diminished. Cant remember how they covered the entrainment of air wth the spray though. And this technique may be outdated- the idea originated in Sweden IIR.
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Cheers Kurnal,
Obviously the compartment door would have to be opened to do that which defeats the logic? Sorry if I'm missing something.
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The thinking when I was in the job was to observe the signs of the smoke behaviour at leakage paths from the fire compartment and without intoducing air to give the upper part of the room repeated blasts with a water mist/ fine spray to reduce the temperature and replace the flammable atmosphere with a steam laden one. Ventilation can then follow once the back draught risk has diminished. Cant remember how they covered the entrainment of air wth the spray though. And this technique may be outdated- the idea originated in Sweden IIR.
This is the way I understood it should be done aswell, using 'door entry procedures' in a team of two. First FF positions him/herself behind the door and is ready to open it for a second maybe two on the second FF's command who is positioned out of the direct path of the door (ie to one side behind the wall). when ready the 2nd FF gives the command to open and immediately puts the HR in directed at the ceiling and lets off two or three quick sprays of water then quickly retracts the HR and resumes the rest position ready to repeat the exercise, thius works by cooling the combustible gases within the compartment and eliminating the danger of a Backdraught.
It has to be said that this is a really dangerous situation to find yourself in and I thought all FF's were taught how recognise the signs and deal with it correctly and safely, the above is a skill which should be practised, you probably won't get a second go on a job!. When you do it a good tip is to be careful where you position the HR in relation to your buddy's hands, any water wasted on their hands could cause them burns in a hot compartment.
This is just the way I've been shown, that said we haven't fully intergrated the use of positive pressure ventilation attack yet so I guess there could well be a different method using the PPV!
Lawman,
Ask about it and do a course or some proper on station training, it's a skill you definitely need to have!!
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Cheers,
Just through my BA refresher and quite happy with the door opening procedures and temperature checks etc. I would however hesitate to open a door where there was pulsing smoke issuing without considering outside ventilation.
Thanks for your help.
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Lawman
You are quite right in saying that opening the door goes against logic, but unfortunately if you want to enter the compartment and carry out a rescue or fight the fire offensively,your going to have to enter at some point.
The main point to note is to ensure that when you open the door you are positioned behind the door (if inward opening) or behind the wall next to the door standard (if outward opening). This will provide you with a bit of shielding in the event of a backdraft and deflect some of the force.
Unfortunately my FRS does not employ the use of PPV, so we have to do it hard way!
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Cheers,
I appreciate your help. Guess so far I've been lucky!
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Cheers Kurnal,
Obviously the compartment door would have to be opened to do that which defeats the logic? Sorry if I'm missing something.
Not quite right Lawman
Correct door check procedures and "water hanging" which is where you apply a fine mist at the top of the door to the compartment you wish to enter before opening it can avoid backdraughts
Essentially you come to the door you wish to enter - spray a fine mist at the top of it first (water hanging)
Then adopt a crouched position using the door or wall as protection and then crack open the door just enough to allow the hose branch in
You then apply three quick water pulses as follows:-
One aimed at the ceiling....
One aimed in the middle and one at the bottom.
So log as you dont open the door fully you should not get a backdraught. Any products of combustion coming through the door should be cooled / displaced by steam by the short pulses put into the room and any residual products of combustion ejecting from teh compartment dealt with by the water hanging effect.
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Thanks MR,
I can see the logic in that. It's not a procedure I've been taught but it makes sense.
Dave
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Thanks MR,
I can see the logic in that. It's not a procedure I've been taught but it makes sense.
Dave
No worries mate - I know there's a lot of different techniques operated by different brigades across the UK and no particular "nationalised" procedure.
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Thats exactly what I was taught on my Flashover backdraft course
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One thing that definitely SHOULD NOT be used if a backdraft conditions exist is PPV. PPV will accelerate the backdraft and make conditions uncontrolable for fire crews. I have used PPV under controlled conditions in a training scenario and have blown the PPV across the drill yard!
If such conditiond exost in acompartment the chances of a person surviving is alomost zero.
The safest way to make the situation safe for the crews is to externally ventilate the room/compartment. The exposures of the opening should be covered by a jet (water should not be put into the room), once and if the backdraft occurs this will be the ideal opportunity for crews to enter the room/compartment to deal with the fire.
If an external vent canot be made, crews will have to use the appropriate door opening techniques, and apply water into the gases to attempt to dilute the gases. there is no point going through door opening and water application techniques as they are all different across the country. This technique will take as long as necessary depending on the conditions.
All firefighters across the country MUST receive Fire Behaviour Training as noted in previous DCOL / Health & Safety Notices etc.
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Interesting that there are fairly fundemental differences in some of these posts. I would have thought that there would be an established "procedure" for such conditions
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I carried out my BA course and fire behaviour training at a superb fire behaviour training centre in the 'South West'. I am lucky (some might say unlucky) in that I have experienced backdraught/flashover conditions for real. Using the training I got, which is described in these posts, I delt with these conditions to great effect.
About 6 months back I attended a BA refresher with an East Midlands brigade, that shall remain nameles! I was 're-instructed' as I was told these proceedures were now in-correct. I was told that when you get to the compartment you should do the following:
Spray the door, look to see the temp ect...
Open the door, look in shouting 'fire & rescue service' - DO NOT pulse any water
Wait then open the door again and short pulse spray once
shut the door wait then go in
Now I was not happy with the opening the door and shouting your life story without putting water into the compartment. I was always of the impression that if there were backdraught conditions that opening the compartment without spraying water could hasten the onsett of a backdraught by the admission of oxygen?
I argued my case unsucsessfully and was told that if i did not adopt this 'New' proceedure I would be taken off the run.
Who is right as I think I am?
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That's the wildest one yet!
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Whats wrong with shouting Fire Brigade? By risk assessment the door would be open for a shorter time. Unless you have to translate into various languages of course. Reading from a script may help as you stand outside the open door.
I think youre winding us up. :)
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Pete P. Remember that BA should be treated as a "casualty centred" rescue where there may be persons reported. The idea that you might want to assess the situation "before" you start filling the room with steam and broil the object of your search, is not one which you should dismiss lightly. Remember that as you introduce your jet to the fire gas layer you will drive the neutral plane down towards the floor. This may lose you the opportunity to see under the gas layer and possibly locate a casualty or gather visual information which could help you if and when you decide to enter the compartment. The idea that you might want to have a brief look before you make any decisions is one which I would encourage provided you assess the situation carefully.
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Pete P. Remember that BA should be treated as a "casualty centred" rescue where there may be persons reported. The idea that you might want to assess the situation "before" you start filling the room with steam and broil the object of your search, is not one which you should dismiss lightly. Remember that as you introduce your jet to the fire gas layer you will drive the neutral plane down towards the floor. This may lose you the opportunity to see under the gas layer and possibly locate a casualty or gather visual information which could help you if and when you decide to enter the compartment. The idea that you might want to have a brief look before you make any decisions is one which I would encourage provided you assess the situation carefully.
You would think that we would all be doing something similar. This is surely a very fundemental matter and not one where there should be any ambiguity!
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Lawman we are doing something "similar". Most of the differences are slight and as long as the procedures are carried out with regard to safety of both the person being rescued and the BA crew. If this is done then as long as you assess the situation properly there is no need to be as prescriptive as you seem to want to be. There should always be room for variations in how we do things in order to allow for local needs. As long as we are all ensuring that the way in which we approach F and B scenarios is done using the same fundamental techniques then it really is down to local training and practices.
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Cheers you make a good point and I accept that the techniques described are largely "similar."
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No probs. Good debate though. Makes a change from constant RRO tedia. If I have to endure much more debate on the merits of rising butts v self closers I think I will butt out, although I am sure these things are of the greatest importance to those in FP. No offence meant.
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It's interesting to see peoples different ideas and the variations around the brigades
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When I come to think about it there is actually a bit of variety in the methods different individuals employ on our watch due to the fact that we go for BA refreshers at different times which isn't ideal.
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Lawman do you go to different places for your refresher training? Does the training dept have tutor consolidation policies? In my department we found that due to a variety of backgrounds the trainers were all giving out slightly differing information re things like door opening and branch techniques. Nothing too dramatic but in the interests of consistancy we decided to nominate a lead tutor on each discipline (RTC; BA, FAB etc) and then get them to consult and then come up with a consistant policy which we should all now be applying. It helps insofar as we now have a single point of reference when we need to decide how we are going to teach stuff and it cuts down on confusion.
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Pete P. Remember that BA should be treated as a "casualty centred" rescue where there may be persons reported. The idea that you might want to assess the situation "before" you start filling the room with steam and broil the object of your search, is not one which you should dismiss lightly. Remember that as you introduce your jet to the fire gas layer you will drive the neutral plane down towards the floor. This may lose you the opportunity to see under the gas layer and possibly locate a casualty or gather visual information which could help you if and when you decide to enter the compartment. The idea that you might want to have a brief look before you make any decisions is one which I would encourage provided you assess the situation carefully.
So long as procedures are done correctly you should have very little steam generated!.
The idea with most techniques is to actually get the neutral plane higher and cool the products of combustion. If you get it wrong thats when the good old neutral plane starts to drop fast!
Its all about controlling the ammount of water that you put in.
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Retty, Absolutely right, but as an instructor taking even very experienced hands through live fire wears,I can tell you that the number of times I have had to get down low on the floor quickly to avoid being steamed would surprise you. The amount of steam generated should indeed be minimal but branch operators often get a bit "trigger happy" when they see the hot stuff and can forget to think about what they are doing to anyone in the compartment. Not a serious problem during training wears but one which needs to be addressed to ensure that wearers are thinking about the effects of their actions.
Lawman, Dont mean to be patronising but have you thought about nominating an experienced hand as watch BAi (even if it is only an informal title) and getting him/her to do your research and keep the watch up to speed on procedures. I would think that your brigade has made all the necessary info available on their IT system. In my brigade those on station have in a lot of cases got tired of waiting for the brigade to get to grips with BA refreshers and are taking matters into their own hands (I am not advocating that people make stuff up localy but I can understand their frustration). To give the brigade credit we are now doing good BA refresher courses which are being well recieved but it will take time to get everyone through. I think in our case the reinstatement of Watch BAIs would be a step forward but only if they are given adequate training and support. I think a big problem is that 1/97 is too woolley and has gone too far in allowing brigades to vary procedures for local needs. It could do with describing in more detail the procedures to be followed in some areas i.e. how do you search a room, open a fire compartment door, how do you actually lay a guideline properly etc.
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I think that would indeed be a stop forward and I will suggest it to our gaffer. I will let you know how it goes forward. Many thanks again for an excellent suggestion.
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how do you actually lay a guideline properly etc.
Please don't let that debate start again!!!!
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Sorry, I was'nt thinking.
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Interesting that there are fairly fundemental differences in some of these posts. I would have thought that there would be an established "procedure" for such conditions
I also find it interesting that there seems to be such a wide variety of opinions on this. I always thought it was fairly straight forward concept.
A backdraft is a situation which can occur when a fire is starved of oxygen; consequently combustion ceases but the fuel gases and smoke remain at high temperature. If oxygen is re-introduced to the fire, eg. by opening a door to a closed room, combustion can restart often resulting in an explosive effect as the gases heat and expand.
A flashover is the near simultaneous ignition of all combustible material in an enclosed area.
I will throw this material out to be considered. Check out
http://www.firetactics.com/
CHECK OUT THE PPV SAFETY NOTES AT THE BOTTOM
Backdraft
A backdraft is an explosion that occurs when the heated gases of an oxygen-starved fire are mixed with oxygen and ignite suddenly.
Why Does Backdraft Occur?
• Except under carefully controlled conditions, combustion is rarely complete.
• Some of the combustion elements are not consumed but pass into the surrounding atmosphere in the form of unburned combustible gases.
• Many combustibles begin to smoke before they actually burst into flame.
• Either there is insufficient available oxygen to support fire or the ignition temperature of the material has not been reached.
• The gases and carbon being emitted are flammable.
• Improper ventilation at this time, such as opening a door or window, will supply the missing link, oxygen.
• As soon as the missing oxygen rushes in, the stalled combustion resumes with devastating speed. A backdraft occurs – a virtual explosion
Signs of Backdraft
The following conditions may indicate a backdraft or smoke explosion condition:
• Smoke under pressure exiting through small building openings
• Black smoke becoming dense, greyish yellow
• Confinement and excessive heat
• Little or no visible flame
• Smoke leaving the building in puffs and being drawn back in
• Smoke stained and/or rattling windows
• Muffled sounds
• Sudden, rapid movement of air and smoke inward when an opening is made
• Hot or warm outside walls with little or no fire evident
If visibility through windows is practically nil but no fire is evident (or perhaps only a faint glow can be seen through the smoke), it is reasonable to assume that a fire has been smouldering for some time.
Under these conditions extreme caution must be exercised because a backdraft danger exists. Horizontal ventilation should not be attempted if another option is available.
Backdraft Prevention
If the conditions are recognised upon arrival, every effort must be made to prevent the backdraft from occurring. Prompt and proper ventilation is in order, but even this procedure cannot absolutely prevent a backdraft. There is no sure method of prevention.
Vertical ventilation is usually the best way of mitigating the backdraft condition. Unfortunately, it may not always be possible.
Each enclosed section of the building must be treated as a separate potential backdraft area.
If it is decided that the space cannot be allowed to cool before making entry, horizontal ventilation may be the only available option. Ventilation must be performed in such a manner as to maximise your safety and minimise property damage.
Once backdraft conditions develop within a confined space, you have only a few safe courses of action.
• It may be necessary to simply do nothing but monitor the space until the smouldering fire goes out due to lack of oxygen or fuel.
• Allow the gases within the space to cool below their ignition temperature
• Allow the backdraft to occur, but control its path by vertical ventilation
• Use a piercing nozzle to penetrate the space and accelerate the cooling process
Protecting Yourself from Backdraft
You should not stand in doorways or directly in front of doors, windows, or other openings when the possibility of a backdraft exists. It is safest if you do not stand anywhere within the V-shaped force near an opening. The gaseous products of the backdraft will expand as they come through the opening because of the lesser pressure of the atmosphere outside the building.
It is possible that backdraft may not exist upon arrival but will develop in confined spaces within a building. If you overlook the warning signs, you may find yourself inside the building when backdraft conditions begin to develop.
Flashover is the sudden transition from local burning to widespread burning of all exposed fuels. It occurs when all the contents of a compartment reach their ignition temperatures in a very short span of time, usually seconds. It happens because hot gases are radiating and convecting heat to all the exposed surfaces. Not all fires reach the flashover stage.
Victim survival is highly unlikely. Heat in the compartment goes from 300?C to approximately 1200 to 1400?C in seconds.
Your escape time from this environment is about ½ to 2 seconds before gear failure and serious injury.
• Prior to flashover
? temperature increases rapidly.
? additional fuel becomes involved.
? fuel packages in the compartment give off combustible gases.
Positive Pressure Ventilation Safety Precautions
1. PPV should not be used if backdraft conditions exist.
2. A prolonged application of positive pressure without a ventilation (discharge) hole may cause the fire to flashover because of the volume of air being injected.
3. In heavy fire load situations, PPV may lead to rekindle.
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Before I joined the Brigade many moons ago I was in the Royal Navy. Then, as part of initial training, we all had to undergo ship fire training.
To enter a compartment we used a water wall and jet through 2 x 70mm supplies. The water wall was created with a special branch which formed a 360 degree perfectly formed wall of water which could extend out numerous metres from the branch. This was used to ensure a constant protective barrier when opening a door or hatch. When the door or hatch was fully opened the water wall was used to maintained a cooling barrier between a fire and the operators. The jet could then be played through the water wall and as long as the branch itself did not obstruct the wall the effective was maintained. It was a very good system and I was extermely surprised when I joined the Fire Brigade to find out that it did not use such a technique.
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The kind of jet pattern you describe used to be available on our standard issue branch, the AWG, with a solid jet in the centre and a water curtain around it (this is 20 years ago in an LAFB). While I can see it would be useful in dealing with the enourmous heat build up in a ship fire I am not sure if it could be used to prevent or deal with a backdraught.
As far as flashovers are concerned there is some debate about whether or not modern hosereels and the branches now commonly used with 45 mm actually deliver enough water to reduce compartment temperatures in order to forestall flashover. This has been particularly questioned in high-rise fires where compartment design (concrete box, sealed unit double glazing, possible high wind speeds) prevents heat dissapation by means other than the front door.
Therefore it could be that your recollection of the efficiency of large jets may well be more than lamp swinging ;-)
Paul Grimwood is the absoloute source on this kind of thing.
website : http://www.firetactics.com/PAUL-GRIMWOOD.htm