Principles of Fire Behavior Additional information for MINA Principles of Fire Behavior; James G. Quintiere; Delmar Publishers; ISBN 0-8273-7732-0

What is Fire? An uncontrolled chemical reaction producing light and energy sufficient to damage skin Also identified as combustion – a chemical reaction involving fuel and an oxidizer in the air Think kilowatts Will there always be light in a flame? No, e.g., burning of hydrogen with air or oxygen produces only water vapor from the reaction. Chemical reaction -

Natural Causes of Fire Lightning Extreme weather Earthquake Key for the investigator Lightning greatest natural cause Winds can cause power lines to fall as will ice storms Earthquakes interrupt power and fuel sources

Man Made Causes Open flames Explosive environments Inattention Chemical reactions Whether unintentional or intentional, uncontrolled fires will happen that will cause damage – Great Fire of London; Chicago Fire; Others Explosive environments would include the grain bins, wood or carpentry areas; metal shops; paint shops; others

Types of Fires Diffusion flames Smoldering Spontaneous combustion Premixed flames

Diffusion Flames A combustion process in which the fuel gas and oxygen are transported into the reaction zone due to concentration differences – Fick’s Law Move from high to low concentration in the mixture Natural flaming fires are diffusion flames Match or candle

Diffusion Flames Terms identifying diffusion flames Pyrolysis – decomposition process as in wood Laminar – pure molecular diffusion as in a candle Buoyancy – gravity or lack of gravity with hotter or lighter gases Jet flame – high pressure created by gaseous fuel sources

Smoldering Slow combustion process Charring - >1000 degrees Solid fuel source Produces deadly levels of carbon monoxide Examples Cigar Upholstered chair Charcoal grill You are investigating a base housing fire. The military member was found in the fire burned. First question would be to ask why didn’t the guy get out when the chair he was setting in caught fire? He falls asleep with his cigarette in hand. It falls in the chair and begins to smolder. Massive amounts of CO is created, incapacitating him before the chair finally ignites.

Spontaneous Begins with a slow oxidations in a fuel exposed to air Very little heat lost Thermal runaway Examples Haystacks Sawdust bin Oily rags piled

Premixed Flames Mixing of fuel gas and air or oxygen Mixed before ignition and propagation Controlled would be jet engines and oxyacetylene torch Uncontrolled examples Confined space Methane leak

Premixed Flames Concentration limits Gaseous fuels will ignite within limits Upper (UFL) Lower (LFL) – temperature just before fuel condenses to a liquid at the LFL is call the flashpoint Autoignition temp (AIT) – lowest temp to cause spontaneous ignition

Heat Transfer Conduction – a molecular phenomenon Convection – conduction in a moving fluid Radiation – an electromagnetic phenomenon Heat Flux – the flow rate of heat – key to assessing the potential damage by a fire A lot of formulas necessary to determine the type of fire and how heat is transferred. In this subject there is the discussion of flashover. This is an evet that can occur at a some temerature of 500 to 600 degrees C in which flames will suddenly fill a room. (page 61)

Ignition Piloted – process of initiation and flame propagation in premixed fuel systems – e.g., welding, jet engines, gas stoves Autoignition – no spark or flame source

Ignition Evaporation – the process of gas molecules escaping from the surface of a liquid Humidity – higher the humidity, less evaporation in the air – lower, more Flashpoint – temp of a liquid fuels and the LFL – point of piloted ignition Boiling point – temp that liquid can evaporate under normal atmospheric conditions What does the MSDS state for the product that was used in the mishap? What environment was the product used???

Flame Spread The process in which the perimeter of the fire grows Wind aided Opposed flow Pyrolysis or vaporization region Burning rate Yes, as an investigator you need to understand how that flame spread like it did. Fire spread – process of advancing a combustion front Wind aided – air flow in the same direction as the fire spread Opposed flow – air flow in the direction opposite to the fire spread Pyrolysis – breaking up a substance into pther molecules as the result of thermal decomposition Burning rate – the consumption of fuel mass per unit time (page 84) Natural flow – air flow induced by buoyancy (gravity) Forced flow – produced by wind or a fan (page 87)

Flame Spread Surface flame Downward/lateral wall spread – opposed flow flame spread Spread through porous solid arrays – brush/debris Spread on liquids – viscous/surface tension For the downward or lateral wall spread, this is when the surface temperature is above a critical value. When addressing what wall surfaces should be, this is a point of action. What is the room going to be used for and how do we need to protect the occupancy. Paints and wall covers can affect how a fire can spread. Viscous – fluid friction Surface tension – force within the surface of a liquid Refer to ASTM E 162 and ASTM E 648 for the various tests that are conducted to determine flame spread of materials that are used in construction. You are asked to evaluate a self help project. The project is putting up walls for an interior office and maintenance room. It has the required number of doors/exits and lighting is going to be wired by CE. What maintenance? What kind of wall surface? Is it adequate for the risks of the work being done in the room?

Burning Rate The mass of solid or liquid fuel consumed per unit time Mass loss rate – the mass of fuel vaporized but not necessarily burned per unit time This may not be a factor when investigating the mishap involving a fire, but when evaluating the scene, you will probably encounter mass loss rate or fuel that may not have burned. An organization wants to use plexiglass instead of glass for the interior office they are building. From a fire safety standpoint, what is the concerns? What type of flame can be expected? An exercise: take small wooden sticks (4x1/4x1/4) and in one stack pile with all the sticks in contact. The next pile leave 1/4in space between the sticks as you stack them. Which one burns? Which stack or pile had more surface exposed?

Fire Plumes Turbulent fire plumes – the flame and gases emanating from a burning object Buoyancy – effective force on fluid due to density or temperature differences in a gravitational field Entrainment – the process of air or gases being drawn into a fire, plume or jet

Fire Plumes Flame height – the vertical measure of the combustion region Pool fires Line fires Eddies – rotating regions of a fluid Vortex – a ring of eddies Flame lengths – depends on energy released There have been some major fires that were so intense because of the elements described in this section. Petroleum and grain elevator fires are known for the intensity of the fire plumes.Pool fires involving horizontal fuel surfaces, usually symmetrical Line fires are elongated on a horizontal fuel surface

Combustion Products Products – chemical compounds produced by fire Yield – the mass of product produced per unit mass of fuel supplied Concentrations – the percentage of material per unit mass (or volume) of its mixture There are other terms that are discussed in the text but not important for the general investigation.

Concentration The primary hazard of fire is the composition and associated concentrations of the smoke Hazards Vitiation – reduction in oxygen Narcotic gases – narcosis Irritant gases – acid, hydrocarbon byproducts Smoke visibility Hyperthermia – heat stress Page 157

Compartment Fires Stages of fire development Developing fire Flashover Fully developed 1. Developing fire – Following ignition, the fire grows on an item and may involve other items. Behaves as if it is burning in the open air for the most of the period. 2. Flashover – dramatic increase in fire conditions due to the confinement of the room. rapid ignition due to heat flux increasing Accumulation of fuel rich gasses and their sudden exposure to air – backdraft The increase in the burning rate and sudden extension of flames (See page 170) Other terms that will be found in the flashover: Ventilation-limited and ventilation-controlled. 3. Fully developed – flames fully encompassing the room, flames, fuel involved is a maximum potential.

Compartment Flow Dynamics Layers and vent flows Smoke filling Smoke movement

Fire Analysis Fire safety design Detection and design Mitigation of growth and suppression Egress Continuity of operations Structural integrity Refuge and rescue

Resources Firedynamics.com www.campusfire.org www.campusfiresafety.com www.pp.okstate.edu/esh/Fire.htm www.fpemag.com www.ul.com

Resources American Fire Journal Fire House Fire Chief Fire Engineering Fire Technology USFA – Fire Data Analysis Handbook USFA FDA Handbook free download – good reference www.fs.fed.us www.nafri.gov ISFTA – Pubs for refiew