VIDEO: This smoke is telling you it's coming @ 4:50
FLASHOVER is a leading cause of firefighter injuries and deaths. Approximately 10% of LODD are a result of rapid fire development: flashovers, backdrafts, wind-driven flame fronts. The potential for flashover is present at almost every working fire. With improved safety equipment, it has allowed firefighters to expose themselves to higher temperatures. Body parts once used as indicators of heat buildup are now covered. The signs of flashover must be recognized to reduce the risk of injury.
TIP: Be aware for the potential of a backdraft or smoke explosion when fire reaches an attic or cockloft space.
LODD: Baltimore County MD. Fire modeling analysis VIDEO explaining flow path, fire spread, travel, smoke behavior and flashover.
FLASHOVER: The near-simultaneous ignition of most of the directly exposed combustible material in an enclosed space. Flashover occurs when a majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases. Flashover occurs at 932°F-1,100°F. Considering human skin burns at 124°F, a face piece will melt at 500°F and most bunker gear chars around 520°F, the survival time for a firemen caught in a flashover is around 5-10 seconds. If caught in a flashover with no way to extinguish it, direct flame contact will cause burns to begin in 2 seconds; fatal burns occur in 15 seconds. Flashovers can't always be handled with a charged hoseline so if extinguishment is not possible, escape quickly or die.
ROLLOVER: Rollover is the ignition of the gas layer under the ceiling leading to total involvement of the compartment; a sign of impending flashover. Immediate water application or else: REMEMBER where your secondary means of egress is!
Some of the signs firemen should look for when determining whether a flashover is likely to occur:
*The fire is in a ventilated compartment, so there's no shortage of oxygen in the room. (Free burning-high heat)
*The neutral plane is moving down towards the floor.
*All directly exposed combustible materials are showing signs of pyrolysis.
*Rollover or tongues of fire appear. Rolleover generally precedes flashover.
*There's a rapid buildup of heat given off by the rapidly burning gases. A good indication of flashover!
*Firemen are forced to stay low because of intense heat.
*Smoke is dense and turbulent often with a distinct thermal layer.
*Flashes of flame are visible through the smoke at the top of windows, door openings, or ceiling level.
LODD: A firefighter/paramedic was killed in this house fire. Notice the turbulent dense black smoke exiting from the front door on side A and the window on side B (above left). This is a warning sign of flashover. The second firefighter/paramedic and the victim were between the fire and vent points. The firefighter who survived had to be rescued 4 feet from the door as her bunker gear was melted into the carpet. See LODD report here.
READING SMOKE TRAINING VIDEO
One of the most important skills all firemen must possess in todays fire environment is the ability to read smoke. Experienced firemen have been reading smoke for years, but recently it has become more of an art. Reading smoke has become a more focused subject of training thanks to firemen like David W. Dodson who authored 'The Art of Reading Smoke.'
Whether it's the incident commander, company officer, pump operator or a probationary member of the ladder company, everyone on the fireground must have the ability to read smoke. In the modern day fire service we may be responding to fewer fires, but we are also responding to hotter more volatile fire environments thanks to low-mass synthetics (plastics) and increased fire loads. We can no longer rely on just experience alone or the "old way" of reading smoke. Though not an exact science, the ability to read the smoke can help us make better tactical decisions. It can help us determine the fires location, growth, toxicity, direction of travel and whether it's going from a contents fire to a structure fire. Most importantly, it helps us predict hostile fire events like smoke explosions, backdrafts and flashovers. Obviously when it comes to location and extent, having a well-ventilated fire showing on arrival is often a good thing, and preferred over smoke coming from every opening as fire is the end product of the combustion process. When only smoke is showing, you have to locate the fire while evaluating its volume, color, movement, velocity, in addition to where the tallest smoke is.
New or inexperienced firemen and company officers MUST learn how to read smoke properly by watching training videos and actual hostile fire events caught on video, especially since THEY will be the ones performing primary searches, horizontal ventilation and operating the handlines in todays structure fires. They must have the ability to recognize and predict fire events before it's too late. Nozzlemen shouldn't always rely on the company officer behind them to give them warning signs of flashover. In a loud fire environment, communications and warnings may become muffled during SCBA use. It's critical to know when to apply water to smoke overhead and perform horizontal ventilation correctly. When making the "go or no-go" decision, the company officer should take a few extra seconds to assess smoke before rushing into the fire building. Even a pump operator with the ability to read smoke and predict hostile events-collapse may see something from the street that interior crews can't and warn them by radio.
Black Fire is turbulent, dense, high-volume black smoke that is ready to light up. Black fire is a sure sign of autoignition and flashover, so treat it as you would actual flames by cooling and venting. Black fire has the ability to do what flames do- charring, heat damage to structural supports, destruction and death. 'Black Fire' can reach temperatures of more than 1000°F.
"When fire makes contact with a surface, it off-gasses black smoke quickly. The blacker the smoke the hotter it is. High velocity black smoke is indicative of flame-pushed smoke. The fire is nearby."- David W. Dodson
Smoke has four attributes: volume, velocity, density and color.
Volume tells little about the fire, but indicates the amount of fuels off-gassing within an area. There can be large volumes of smoke with very little fire.
Velocity is the speed of the smoke leaving the structure. It indicates the pressure (heat and volume) built up inside. If the velocity is turbulent, a flashover is evident. Turbulent smoke is ready to ignite and indicates a potential flashover or smoke explosion.
Density of smoke refers to its thickness and how much fuel is laden in the smoke. The thicker the smoke, the more spectacular the hostile fire event. Thick black smoke is ignitable fuel.
Color tells the stage of heating and helps determine the location of the fire. It's not always going to tell you the type of material burning as most residential and commercial fires are not single-fuel fires, but a mix of colors leaving the structure. Wood burns brown/tan, hydrocarbons/petroleum, rubber burn black, plastics/paints will emit gray smoke as a result of the mixing of moisture and hydrocarbons. Wood and ordinary combustibles will produce smoke ranging from light gray to yellowish, dark brown or even black when the fire is underventilated. WATCH HOSTILE FIRE EVENTS CAUGHT ON VIDEO BELOW
The amount of fuels found in the modern fire environment have substantially increased due to most consumer products being made of petro-chemical based plastics. The amount of fuel available to burn has also increased in homes and businesses as a result of big box bulk purchasing. These low mass synthetic fuels have high heat release rates and decompose rapidly producing super-heated smoke and gases within the container. Gases expand when heated, will become less dense and rise. When gases are confined and heated, pressure increases indicating higher temperatures. These modern "room and content" fires are more volatile, reaching over 1000°F before flashover. Smoke is unburned fuel and the hotter the fuel, the closer it is to its ignition point.
TIP: Brownish smoke will tell you that fire has ignited wood, which usually means the room and contents fire is now a structure fire as the structural members are starting to burn. Generally, lighter color smoke contains a concentration of unburned pyrolysis (highly flammable) products. Under these conditions, smoke can still ignite (with adequate oxygen and ignition source).
Velocity: Pressure of the smoke leaving openings. Turbulent smoke and rollover are warning signs of flashover. Velocity of smoke can also help in locating the fire.
Perfect video showing the anticipation of flashover. You know it's coming at 10:00 second mark. Watch the 'build up' and speed, velocity, color, FLASH...
CARBON MONOXIDE SMOKE EXPLOSION
This 3rd floor smoke explosion in a SFW may have been caused by build up of carbon monoxide in the attic that was fed by the high BTU materials on the porches that ignited. These hostile events occur in attic spaces, drop ceilings, or any confined space where high levels of carbon monoxide and high heat can build up.
KNOW THE SIGNS OF FLASHOVER!
TIP: (NFPA) A compartment fire is any fire within a structure that has a roof and at least two enclosing perimeters (side walls) which can be either parallel or perpendicular. (Compartment, Room, Container)
Remember, today's buildings are more tightly sealed with double-pane glass windows, built with lightweight building materials, filled with highly combustible furnishings and plastics. This results in greater amounts of heat and flammable gases present.