Chapter 7

Reading Smoke

Objectives

• Define “smoke”

• List common hostile fire events and their associated warning signs

• List the four attributes of smoke

• Describe what each of the four smoke attributes contributes to the understanding of fire behavior in a building

Objectives (con’t.)

• Define “black fire” and its relevance to firefighting efforts

• Explain how influencing factors can affect smoke attributes

• List the three steps in the reading smoke process

Introduction

• History of reading smoke– Older practices of reading smoke based on

experience and intuitiveness– Low-mass synthetics and the consumer “glut”

in the 1990s led to a more volatile smoke and fire environment

– Current trends of reading smoke triggered by ISO Academies in 1990s

• Developed by David Ross and David Dodson

“Smoke” Defined

• Smoke– Product of incomplete combustion– Aggregate of solids, aerosols, and fire gases– Toxic, flammable, and volatile

• Four key attributes of smoke– Volume– Velocity (pressure)– Density– Color

Table 7-1 Properties of gases typically found in smoke.

“Smoke” Defined (con’t.)

• “Open flaming” is desirable– Products of combustion are minimized– Smoke displaces air in underventilated fires

• Two triggers cause accumulated smoke to ignite– Right temperature– Right mixture

• Watch smoke instead of focusing on flaming

Hostile Fire Events

• Events that can catch firefighters off guard and endanger them– Flashover– Backdraft– Smoke explosions– Rapid fire spread

• ISOs must know and watch for proactive warning signs of hostile fire events

Table 7-2 Hostile fire events.

Volume, Velocity, Density, and Color

Figure 7-2 Comparing smoke volume, velocity, density, and color can help the ISO understand fire behavior. (Photo by Keith Muratori.)

Volume, Velocity, Density, and Color (con’t.)

• Volume– May indicate the amount of fuel that is off-

gassing in a given amount of space– High volume of smoke can occur with:

• Hot, fast moving fire in an underventilated building • Dampened material• Low mass contents

– High volume of smoke can create the impression of a fire

Volume, Velocity, Density, and Color (con’t.)

• Velocity– Speed at which smoke leaves a building– Indicator of pressure within building– Turbulent smoke flow

• Ready to ignite• Flashover is likely to occur

– Laminar smoke flow• Stable and smooth smoke flow• Heat of smoke is being absorbed

Volume, Velocity, Density, and Color (con’t.)

• Density– Refers to the thickness of smoke– Indicates how much fuel is laden in the smoke– Thick smoke spreads a fire event farther than

less dense smoke– Thick black smoke in a compartment reduces

the chance of life sustainability

Volume, Velocity, Density, and Color (con’t.)

• Color– Indicates the stage of heating– Points to the location of the fire in a building– The more black the smoke, the hotter the

smoke• High velocity, low density black smoke is flame-

pushed• Interpreted, thin black smoke indicates nearby open

flaming

Volume, Velocity, Density, and Color (con’t.)

• Color (con’t.)– Can indicate distance from fire

• Fast moving white smoke has traveled

– Brown smoke from structural spaces• Indicates transition from a contents to a structural

fire

• Watch for the fastest/darkest smoke from the most resistive crack (Dave Dodson)

Figure 7-5 Smoke that appears the same color and velocity from multiple openings indicates a deep-seated fire. (Photo by Keith Muratori.)

Volume, Velocity, Density, and Color (con’t.)

• Black fire– Slang term to describe high-volume, turbulent,

ultradense, and deep-black smoke– Sure sign of impending autoignition and

flashover– Can reach temperatures of over 1,000 degrees

Fahrenheit– Solution: vent and cool!

Other Factors That Influence Smoke

• Weather– Temperature, humidity, and wind change the

look of smoke– Cold air cools smoke faster, causes it to

stall/fall, and turns it white– Humidity increases air resistance to smoke– Wind-fed fires can cause firefighters to be

overrun

Other Factors That Influence Smoke (con’t.)

• Thermal balance– Notion that heated smoke rises and creates a

draft of cool air into the flame source– Not maintained in most fires within buildings– Indicated by air being sucked into a building

• Intense fire struggling for airflow• Sudden inflow of air can trap firefighters

Other Factors That Influence Smoke (con’t.)

• Container size– All smoke observations must be analyzed in

proportion to the building– Size of the building is an important indicator of

the significance of the smoke leaving it• Example: light, thin smoke showing from more than

one opening of a very large building may indicate a large, dangerous fire

Other Factors That Influence Smoke (con’t.)

• Firefighting efforts– Four attributes of smoke should change in a

positive manner if fire stream and ventilation efforts are appropriate

• Volume should rise• Velocity should gradually slow and change to

laminar flow• Density should thin• Color should eventually turn white

Other Factors That Influence Smoke (con’t.)

• Firefighting efforts (con’t.)– Forced-ventilation tactics should cause an

increase in smoke velocity– PPV tactics are contraindicated if:

• Smoke is turbulent• Location of fire seat is unknown• Fire is in a vented, combustible void space• Smoke become thicker and darker during PPV use

Reading Smoke: The Three-Step Process

• Step 1– View the volume, velocity, density, and color of

smoke– Compare the difference in the attributes from

each opening from which smoke is emitting

Reading Smoke: The Three-Step Process (con’t.)

• Step 2– Analyze contributing factors (size, weather,

firefighting efforts) to determine if they are affecting volume, velocity, density, and color

• Step 3– Determine the rate of change of each attribute

• If deterioration can be measured in seconds, firefighters are at risk

Table 7-3 Reading smoke shortcuts.

Summary

• Predicting fire behavior is based on understanding:– Physical and chemical properties of smoke

• Volume, velocity, density, and color

– Proactive warning signs of hostile fire events– Factors that influence smoke

• Weather, container size, thermal balance, and firefighting efforts

– Rate of change in smoke attributes