A low concentration of oxygen will slow the burning right down. An example of dangerous fire behaviour that can occur in a situation where there is a low concentration of oxygen is called backdraught.
This is when an enclosed fire has used up most of the oxygen and is just smouldering. If there is a sudden influx of oxygen like someone opening a door or window , the fire will immediately explode into flame.
Relative humidity: This reflects the amount of moisture in the air. If relative humidity is low, it will contribute to the drying of fuels. If it is high, fuels will absorb moisture from the air, making ignition more difficult. Wind: This is a major factor in determining fire spread. Wind affects the rate of oxygen supply to the burning fuel controlling combustion and it tilts the flame forward so that unburned fuel receives energy by radiation and convection at an increased speed.
Wind can also dry out the fuel. Rainfall: This also has an effect on wetting fuels, but absorption of moisture is dependent on fuel size.
Fine fuels absorb moisture more quickly than coarse fuels. Lack of rain precipitation is the biggest factor affecting the drying process of fuels. Increased temperatures: These will dry out potential fuel so that there will be less preheating of fuels to reach ignition temperature.
The terrain shape of the land has significant influence on wildfire behaviour. Steep slopes may increase fire speed because fuels scrub and vegetation are preheated ahead of the fire through convection and radiation. Rugged terrain with narrow valleys, sharp ridges and irregular slopes affect the direction and rate of fire spread. For example, narrow valleys can funnel winds, increasing the rate of spread of a fire due to convection.
How Hot Does it Get? The first thing you need to know about fire is that heat rises and so does smoke. Both of these things can make a big difference in a fire. That means the lowest temperature in a fire is usually at the same level as your feet. In a typical house fire, the floor will reach at least degrees, but often much hotter. This is hot enough to be very uncomfortable and potentially give long enough exposure to it — it can burn you.
However, if you move up just a little to your eye level the heat will usually be around degrees. So, this is very hot, indeed. By the time you get to the ceiling, things tend to be super-heated. When things are that hot, your clothes quite literally melt onto your skin and you can burn your lungs just by breathing the air at this temperature. Very dangerous. That is why we are always told to stay low in a fire, the temperatures are much more tenable and it tends to be less smoky for breathing.
Firefighters use thermal imaging cameras TICs to help with visibility and read temperatures in a fire, check it out:. Can a house fire get hotter than 1, degrees? Well, yes, it can. If, on the other hand, the house is full of flammable materials think propane used for welding or gas supply then things could get hotter still.
A full-on propane fire can breach 3,50 0 degrees! Carbon monoxide poisoning causes more fire related deaths than any other toxic product of combustion.
When the smoky layer inches down to the top part of a doorway, an open window or a vent, it quickly streams out of the room. Then the poisonous smoke and heated air travels through hallways and up stairwells to the second floor.
The fire consumes kitchen cabinets, wood countertops and shelves stocked with plastic storage containers and dry goods like cardboard boxes of cereal, crackers, and cookies.
More and more heat is generated. The temperature in the upper layer of hot gases rises to degrees F—hot enough to kill people. Compounding the heat is a very dense smoke cloud hovering just a few feet above the floor. It may also include more toxic components like arsenic used as a wood preservative and lead from old paint , as well as irritants like ammonia, oxides of nitrogen, hydrogen chloride and isocyanates.
The fire can now spread by two paths: direct flame contact or by auto-ignition, the temperature at which objects will spontaneously burst into flames without being touched by flames. The auto-ignition temperatures of hard and soft wood used in furnishings and home construction fall between degrees F to degrees F.
As this happens, flashover occurs. Everything in the room bursts into flames—wood dining table, wood and upholstered chairs, cookbooks, curtains and wall decorations. The oxygen in the room is virtually sucked out used up during the rapid combustion ; glass windows shatter. Balls of fire and flames shoot out windows and doorways. The upstairs fills with thick, hot, noxious smoke and the stairwell is impassible. When you have flashover in a room, temperatures can reach up to 1, degrees F—now, all of the other rooms in the house are severely at risk.
Flames pour through the doorway into the neighboring living room, setting the carpet and upholstered furniture on fire. Synthetics like polyurethane and polyester foam in sofas, pillows and carpets release tremendous amounts of heat.
The temperature above the sofa quickly rises to degrees F. Back in the kitchen, the blaze has penetrated the wall and ceiling and flames travel quickly through unseen structural vertical shafts in interior walls and horizontal shafts between floors. Fire spreads to the second floor. Flames are visible from the street: they travel outside the house through the door and broken windows and into open second story windows. Rescuing anyone still trapped on the second floor may be impossible.
As the blaze in the living room intensifies, the room flashes over. The type of construction materials used to build your home will influence the severity of damage. Synthetics like polyurethane, polystyrene, and PVC used in glues, insulation, and plumbing will auto-ignite at temps between and degrees. At degrees F, steel plates used in engineered roof trusses will start to buckle and they lose 40 percent of their load-carrying capacity.
Newer homes built with engineered wood can experience floor collapse in as little as 6 minutes. Roof collapse can follow very soon after in an out-of-control blaze. If flames are visible from the outside when firefighters arrive, they immediately go into an aggressive attack strategy trying to ascertain if they can still safely save lives.
Next they direct water to extinguish the blaze at the heart of the fire.
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