Chapter 1: Preparation - Behavior of Fire

Comprehensive review flashcards for Chapter 1: Preparation, focusing on the behavior of fire, fire triangle and tetrahedron, classifications of fire (A, B, C, D, K), heat transfer methods, traditional and modern stages of fire, and hazardous fire phenomena including rollover, flashover, and backdraft.

According to James P. Smith, why is firefighting characterized as an art rather than a science?

Firefighting is an art and not a science because you cannot always predict the exact outcome of an event even with good information; instead, firefighters must make predictions based on experience and training, adjusting as the dynamic incident scene changes to protect life and property.

What is the primary operational objective of calculating needed fire flow at an incident scene?

It assists fire officers in determining the personnel needed to handle hose-lines and to implement tactical operations at the scene.

How is the behavior of fire defined chemically?

Fire is a chemical process where fuel, oxygen, and heat come together in an uninhibited chain reaction, involving the rapid oxidation of a combustible material producing heat and flame.

What components make up the fire triangle, and what causes it to cease to exist?

The fire triangle consists of fuel, oxygen, and heat; it will cease to exist if any one of these three elements is removed.

Can fires exist in atmospheres lacking oxygen?

Yes, fires can exist in atmospheres containing oxidizers other than oxygen, such as chlorine.

What practical methods can be used to eliminate fuel from an active fire?

Pumping the contents of a burning flammable liquid storage tank to an isolated empty tank, or shutting off a valve on a pipe flowing burning flammable liquid.

How can oxygen be excluded or reduced to extinguish a fire?

By covering the fire with dirt, foam, a wet blanket, or placing a lid over a burning pan of oil, or by blanketing the fire with a heavier-than-air gas like carbon dioxide ($\text{CO}_2$) to displace oxygen.

Through what two successive physical processes does water extinguish a fire by cooling?

Water absorbs heat first by being raised to its boiling point, and second by being converted from boiling water into steam.

What fire concept is illustrated in this diagram, and what is its extinguishing principle?

The fire tetrahedron; it represents an uninhibited chemical chain reaction occurring when fuel is broken down by heat, which is extinguished when the chemical chain reaction is interrupted by an extinguishing agent.

Into how many classes does the United States categorize fires for extinguishment purposes?

Five classes: Class A, Class B, Class C, Class D, and Class K.

What materials are involved in Class A fires, and what additives can increase water's effectiveness on them?

Class A fires involve ordinary combustible materials (such as wood, paper, and textiles); water additives include wet water, Class A foam, and high expansion foam.

Which NFPA standards address wetting agents, water additives, and Class A foam?

"NFPA 18: Standard on Wetting Agents," "NFPA 18A: Standard on Water Additives for Fire Control and Vapor Mitigation," and "NFPA 1145: Guide for the Use of Class A Foam in Manual Structural Fire Fighting."

How does wet water improve the extinguishment of deep-seated Class A fires?

It reduces the surface tension of water, allowing it to be much more easily absorbed by burning materials such as bales, overstuffed furniture, and mattresses.

How does Class A foam function to extinguish fire and protect unburned materials?

It is a liquid foam solution made by introducing air into a mixture of water and concentrate; its bubbles adhere to surfaces, gradually releasing water over a larger contact area to maximize heat absorption, while surfactants reduce surface tension to penetrate deep-seated fuel.

What are the expansion ratios of high expansion foam, and what structural openings are required for it to work?

Expansion ratios range from $200\text{ to }1$ up to $1000\text{ to }1$; it requires one opening for the foam to be introduced and another ventilation opening past the fire area so the foam can flow through and fill the space.

What are the characteristics and water stream distance of a pressurized water fire extinguisher?

It contains water (and optionally a wetting agent), is pressurized by an air compressor, is effective on small Class A fires, and produces a stream of $40\text{ to }50\text{ feet}$.

What chemical agent is in multipurpose dry chemical extinguishers, and what is its chain-breaking extinguishment mechanism?

It contains ammonium phosphate; upon discharge, it thermally decomposes and interferes with the combustion chain reaction, reducing the concentration of free radicals present in the flames.

What class of fire is identified by this symbol?

Class A fires, marked by a green triangle containing the letter A, involving ordinary combustible materials.

What fuels are involved in Class B fires, and what is the standard extinguisher marking symbol?

Flammable liquids, combustible liquids, petroleum greases, tars, oils, solvents, lacquers, alcohols, and flammable gases; extinguishers are marked with a red square containing the letter B.

What materials are involved in Class C fires, how are their extinguishers marked, and which agents are used?

Class C fires involve energized electrical equipment; extinguishers are marked with a blue circle containing the letter C; they are extinguished using non-conductive agents, specifically dry chemical and carbon dioxide ($\text{CO}_2$).

How does carbon dioxide ($\text{CO}_2$) extinguish a fire, and what is a distinct advantage of its use?

It is a compressed gas that displaces oxygen surrounding the fire and cools the fuel; a key advantage is that it leaves no residue.

What materials are classified under Class D fires, and what is the general rule regarding water application?

Combustible metals (aluminum, magnesium, titanium, sodium, and potassium); as a general rule, water should not be used on metal fires because reactions can range from minor to explosive (with rare exceptions for large quantities on small fires where explosive reactions must still be anticipated).

What fire classification is represented by this symbol, and where are these hazards commonly found?

Class D fires (combustible metals), identified by a five-pointed yellow star containing the letter D; commonly found in industrial establishments and in automobile fires containing aluminum engines.

What fuels are involved in Class K fires, what suppression system is most effective, and why must multipurpose ABC extinguishers NOT be mixed with it?

Vegetable oils, animal oils, or fats in cooking appliances; the most effective system is a wet chemical commercial hood suppression system; multipurpose ABC extinguishers threaten the foamy layer and cooling ability of the wet chemical agent, which can damage cooking appliances.

How are Class K fire extinguishers marked, and how do they differ from Purple K extinguishers?

Class K extinguishers are marked with the letter K or a black hexagon containing the letter K; they should not be confused with Purple K extinguishers, which are designed for Class C (and B) fires.

What five primary factors determine whether an unabated fire will spread to nearby structures?

Amount of heat generated by the fire, distance or spacing between buildings, duration of the fire, height of the buildings, and type of building construction.

What is heat conduction, and how can it cause fire extension between adjoining buildings?

Conduction is the transfer of heat through direct contact of materials from higher to lower temperature until equalized; for example, floor joists sharing the same wall socket in adjoining buildings can conduct heavy fire undetected into the neighboring structure.

How does convection spread fire through a structure, and why are multistory single-family residences especially vulnerable?

Convection is heat conducted by gas or liquid where rising air currents mushroom at the ceiling, spread laterally, and bank downward; multistory single-family residences are vulnerable because staircases are usually unenclosed, offering an unimpeded convective path to upper floors.

How does radiant heat travel, and how can exposed buildings be protected from radiated heat?

Radiant heat travels as rays in straight lines in all directions from the fire (including back toward the fire, accelerating chain reactions); exposed buildings are protected by applying water streams to their exterior surfaces to keep them cool and prevent ignition.

What are the five sequential stages of fire development?

1. Ignition, 2. Growth, 3. Flashover, 4. Fully developed, and 5. Decay.

What occurs during the growth stage as the fire area temperature approaches $1000^\circ\text{F}$?

Combustion products bank down, filling the area with superheated smoke and gases; as temperature builds past $1000^\circ\text{F}$, the area nears the flashover stage if sufficient oxygen is available.

What temperatures are associated with the flashover stage, and what physical process occurs?

Flashover temperatures are estimated between $900^\circ\text{F}\text{ and }1100^\circ\text{F}$, with ceiling temperatures exceeding $1300^\circ\text{F}$; gaseous combustion products reach ignition temperature, resulting in almost simultaneous ignition of all combustible surface areas in the space.

What defines the fully developed and decay stages of a fire?

In the fully developed stage, all combustible materials are involved, heat release is maximized, and temperatures can exceed $2000^\circ\text{F}$; the decay stage begins when oxygen or fuel diminishes, burning slows, temperatures decline, and large volumes of smoke containing carbon monoxide are produced.

What stages are depicted in this traditional fire behavior curve?

Ignition, Growth, Fully developed, and Decay.

What are the physical properties and health symptoms of carbon monoxide ($\text{CO}$) exposure?

Carbon monoxide is an odorless, colorless gas; at low concentrations, it causes headaches and dizziness before leading to incapacitation.

What safety equipment was introduced to first responder medical bags following a severe heater CO incident?

Clip-on, continuously active $\text{CO}$ monitors that enter the structure with the first person and sound an alarm when high levels of $\text{CO}$ are encountered.

At what oxygen concentration thresholds does a growth-stage fire become ventilation-limited and subsequently enter initial decay?

A fire becomes ventilation-limited when the oxygen level is reduced to less than $21\%$, and it enters its initial decay stage once oxygen drops below $16\%$.

In modern content fire behavior shown in this graph, what occurs when ventilation or oxygen is introduced during early decay?

Introducing oxygen triggers a second growth stage, which can lead to a ventilation-induced flashover transitioning into a fully developed fire.

What does it mean when a ventilation-limited structure fire is 'venting' rather than 'vented'?

It means fuel-rich smoke and hot gases flow out through an opening and burn outside upon meeting exterior oxygen, while internal conditions remain ventilation-limited with high temperatures inside.

What causes the phenomenon of rollover, and how far ahead of the fire can it occur?

A fuel-rich mixture of unburned combustible gas pushed by the thermal column along the ceiling meets sufficient air to reach its flammable limits; it is often observed rolling $10\text{ to }20\text{ feet}$ ahead of the main fire.

What are four critical warning signs of an imminent flashover?

Intense heat, free-burning fire, unburned articles starting to smoke, and fog streams turning to steam a short distance from the nozzle.

What is the key difference between flashover and backdraft regarding oxygen and fire state?

In flashover, there is adequate oxygen available and the fire is free-burning; in a backdraft, oxygen is depleted and the fire is in an oxygen-deficient, smoldering state with high heat and combustible vapor accumulation.

What tactical action must precede fire attack under backdraft conditions, and why?

Adequate ventilation above the fire is the first priority and must precede fire attack to relieve internal pressure and vent accumulated heat and smoke to the exterior before fresh air triggers an explosion.