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  #1  
Old 09-30-2007, 08:40 PM
RugbyCanada RugbyCanada is offline
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Location: Toronto
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Default Backdraft vs. Flashover Vs. Smoke Explosion?

Hey guys and girls,

Can anybody explain/define the difference of these three phenomena? I have been on quite a few sites {yes, even tried Google--grrrr}, and I cannot find consistant answers.

Any advice/opinions? Thanks in advance.

Cheers,

RC
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  #2  
Old 09-30-2007, 08:55 PM
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hmckay91 hmckay91 is offline
 
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http://www.fire.org.uk/punbb/upload/...hp?id=1873&p=3



Quote:
The Lawman wrote:

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 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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  #3  
Old 09-30-2007, 09:00 PM
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PFD023 PFD023 is offline
 
Location: Ontario
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Rather than develop carpal tunnel.....here's a good link:

http://www.firetactics.com/FLASHOVER_answer.htm

Hope it helps.
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  #4  
Old 10-01-2007, 06:05 AM
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brechmos brechmos is offline
 
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For what it's worth, the other one that people confuse with the a backdraft and flashover is a rollover. A rollover is when the flames and hot gases roll across the ceiling (above you).

Some say that they have been in a flashover, when really what they have been is a rollover. As stated above, it is very unlikely you would survive a flashover. You would likely survive a rollover.
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  #5  
Old 10-01-2007, 12:20 PM
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Wpfd22 Wpfd22 is offline
 
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Just my $.02 on this

The rollover is almost always right before a flashover and should be a warning sign that a flashover is near if the proper steps are not taken when in a rollover. If it was me and I saw the smoke above my head starting to light up I would be getting out of there and try a different approach.
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  #6  
Old 10-01-2007, 04:52 PM
RugbyCanada RugbyCanada is offline
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Location: Toronto
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once again, man am I glad to have found this site. Thanks for the responses, and the above links.

Cheers,

RC
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