화재역학[산업안전보건교육]

Main ideas, concepts, and lessons

Combustion products and toxic smoke

• Combustion products form in solid, liquid, and gaseous states.
• Toxic gases in smoke are a major hazard.
• In recent fires, smoke-related deaths (example given: 74 deaths) account for about two-thirds of total fatalities.
• Smoke spreads faster than heat/flames, so understanding smoke generation and movement is increasingly important.

Why knowledge is increasingly important

• Buildings are supposed to have fire suppression/extinguishing facilities, but in reality not many places have all needed systems.
• Therefore, preventing and controlling hazards like smoke diffusion (including induced smoke) becomes critical.
• If smoke control equipment fails, smoke can spread quickly from lower floors to upper floors, increasing casualties.

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Learning objectives / structure (as stated)

Through the lesson(s), learners should be able to:

• Explain heat transfer
• Explain fire loads and related tasks (subtitle mentions “iodine,” likely a transcription error; context indicates fire-load-related content)
• Explain combustion products and combustion gases
• Explain the generation and movement of smoke

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Heat transfer methodology (detailed)

Basic principle

• Heat transfer occurs when two objects at different temperatures contact:
  • The hot object cools
  • The cold object heats

Three methods of heat transfer (often combined)

1) Conduction

• Heat transfers through direct contact between objects.
• It can occur:
  • Within a material (from one end to the other), or
  • Through a third object acting as a medium.
• Microscopic mechanism:
  • Atoms/molecules vibrate rapidly, transferring energy to neighbors.
  • In solids:
    • Conduction is important through molecular vibrations and free electron movement.
  • In gases/liquids:
    • Conduction mainly occurs through diffusion during molecular collisions.
• Practical implications:
  • Materials with lower thermal conductivity burn more easily.
  • Example: wood (lower thermal conductivity than iron) is easier to burn.

2) Convection

• Heat transfer due to vertical movement of fluids (liquids and gases).
• Mechanism:
  • When the lower part is heated, the fluid becomes heated and moves, distributing heat.
• Examples:
  • A room heated by a fireplace is due to convection currents.
  • Atmospheric convection:
    • Daytime: land heats first → air rises → cooler air over sea moves in → sea breeze
    • Night: sea/land temperature differences reverse → land breeze
• Convection is considered a meteorological phenomenon resulting from atmospheric convection.

3) Radiation

• Heat is transferred without a medium via electromagnetic waves.
• Mechanism:
  • Excited electrons emit or absorb electromagnetic waves when they change energy levels.
• Practical implications:
  • Solar heat reaches Earth because it can travel via radiation.
  • Radiant heat/energy increases with object temperature.
  • Better emitters also tend to absorb radiant heat better.
• Color effect:
  • Black surfaces absorb more radiant heat.
  • White surfaces reflect more radiant heat.
  • People often feel hotter in black clothes in summer.

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Fire load (definition + calculation + implications)

Definition

• Fire load represents the heat output and fire risk of a building fire.
• Expressed as amount of combustible material per unit area (used to determine the fire scale).

Fire load calculation (as described)

• The subtitle provides a formula structure; key meanings:
  • t: mass (kg) of a material
  • ht: unit heat output of the combustible material
  • h: example given for wood (1500 kcal/kg)
  • aen: floor area of the fire room
  • Qt: total heat output of the combustible material
• Interpreted outcome:
  • Fire load can be expressed as kg of combustible material per 1 m².
• Because buildings contain many material types:
  • Actual materials are converted to an equivalent wood amount (same heat output).

Additional stated interpretation/uses

• Fire load helps judge:
  • Scale of a problem (and the fire size)
  • Duration of the fire
• Countermeasures given:
  • Reduce fire load by making interior materials/fixtures non-combustible or flame-retardant.
• “Ownership” is mentioned as a factor:
  • Interpreted as the degree to which fire can destroy/damage the building and contents.
• Fire temperature & peak temperature
  • Peak temperature and fire duration are important in judging fire severity.
  • A stated relationship:
    • Fire duration is determined by water amount.
  • General statement:
    • If fire temperature is higher → greater loss; if lower → less loss.

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Combustion gases (what they are + effects)

Types of combustion products during a fire

• Include heat, smoke, and “continuous combustion” gases (with emphasis on toxic gases).

Carbon monoxide (CO)

• Produced in large quantities during incomplete combustion.
• Effects:
  • Binds to hemoglobin → blocks oxygen transport
  • Paralyzes central nervous system → oxygen deficiency
  • Strong affinity for oxygen → worsens suffocation
• Concentration vs. time (as stated):
  • 600–700 ppm: perceptible after ~1 hour
  • 2,000 ppm: life-threatening after ~1 hour
  • 1,000 ppm: death within ~1 hour

Carbon dioxide (CO₂)

• Not described as toxic in itself.
• In large quantities:
  • Increases human respiratory rate
  • Promotes mixing/incorporation of other toxic gases → increases danger

• Symptoms depending on concentration (as stated):

  • Discomfort, increased respiratory rate, pressure sensation, vomiting, dizziness, difficulty breathing, visual impairment, unconsciousness within about 1 minute

  • If untreated: can lead to death and central nervous system paralysis

Other toxic gases mentioned

• Phosphates: from combustion of flame-including substances; especially noted with carbon tetrachloride
• Oxides: highly toxic; from burning petroleum products/oils
• Sulfur dioxide (SO₂): from complete combustion of sulfur-containing organic compounds
• Hydrogen sulfide (H₂S): from incomplete combustion of sulfur compounds; rotten egg smell
• Chlorine/chloride-related gas
  • Produced when chlorine-containing substances burn (example: seeds)
  • Irritating, filament-like behavior described
  • “Time-limited chlorine” is mentioned (likely a transcription issue); described as water-soluble, highly toxic
  • Referred to as “Cheongsan gas”
• Polyurethane + T5 smoke
  • Mentioned as smoke produced during incomplete combustion
• A cited case notes carbon and hydrogen as main causes:
  • Welding sparks ignited old burnt foam → significant casualties

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Smoke: definition and dynamics (generation + movement)

What smoke is (as described)

• A state where carbon and carbon particles (combustible material not fully combusted) float around.
• Visibility:
  • Visible to the naked eye when particle size is > ~1.0 micrometer.

Why smoke is deadly

• Many fatalities in recent fires were attributed to suffocation from toxic gases inside smoke.

Smoke spreading behavior

• Smoke can:
  • Rise to the ceiling, linger, descend along walls, and spread to the floor
• Example timeline:
  • Smoke spreads up to about 100 meters after ~10 minutes from fire start
• Temperature-driven movement (inside vs outside):
  • If outside temperature > inside: smoke moves downward
  • If outside temperature < inside: smoke moves upward
• Directional speed:
  • Slowest horizontally; accelerates vertically near indoor stair directions.
• Fresh air flow:
  • Necessary fresh air flows in the same direction as smoke flow.

Smoke spread through spaces (pathways)

• Smoke ejected from a fire room is lighter than air:
  • Flows along passages and “spheres”
  • Spreads upward from the ignition layer to upper floors.

Factors affecting smoke flow

• Chimney effect
• External wind power
• Temperature difference between inside and outside
• Forced airflow inside the building
• Vapor expansion due to temperature rise
• Differences in specific gravity
• Buoyancy

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Effects of smoke + visibility factors

Effects on humans

• Reduced cognitive ability
• Visual impairment

Visibility factors (what affects how well people can see)

• Smoke concentration
• Smoke flow velocity
• Luminance and the shape of signage

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Smoke control methods (with detailed mechanics)

Overall goal

• Control smoke using smoke-extinguishing/equipment and design methods.

Blocking (most widely used)

• Exhaust internal smoke to the outside while introducing external fresh air.
• Dilute smoke below a dangerous level.
• Mechanism:
  • Similar to a pressure-difference approach (“bag-in-and-smoke shaft” analogy):
    • Use pressure difference between inside and outside to expel smoke.
• Implementation details mentioned:
  • Install barriers such as:
    • Fire doors
    • Firewalls
    • Fire dampers
  • Use pressure difference between the protected object and the smoke location.

Neutral zone / pressure concept (“final zone”)

• Defined as the region where interior and exterior pressures are equal.
• Pressure behavior:
  • Above neutral zone:
    • Interior pressure is higher → air flows out (inside → outside)
  • Below neutral zone:
    • Outside pressure drives air in (outside → inside)
• During a fire:
  • As height increases, the neutral zone position lowers.
• If the neutral zone lowers:
  • Less outside air enters → smoke flow becomes “inactive”
  • Smoke can descend to the neutral zone and then rise again.
• Venting guidance:
  • Vent smoke effectively from above the neutral zone
  • Caution: it can increase influx of new air, potentially causing smoke to expand more.

Chimney effect

• When outside temperature is lower than inside:
  • Smoke flows due to density transport differences with height
  • Creates pressure differences depending on building height.
• Example described:
  • If a fire occurs on the 9th floor below the neutral zone:
    • Smoke penetrates the interior and rises complementarily
    • Upward speed increases due to the smoke’s temperature and buoyancy.

“Gold-drop effect” factors

• Influencing factors listed:
  • Building height
  • Exterior walls
  • Inter-floor air leaks in a named building (Kim Il-sung Building)
  • Gaps
  • HVAC system termination
  • Inside-outside temperature difference

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Flashover (definition, timing, conditions, and prevention)

Definition

• A fire state where it gradually progresses via heat accumulation, then suddenly erupts into large flame.
• Rapid temperature rise occurs due to simultaneous combustion of flammable gases.
• Described as explosive ignition and momentary combustion expansion.

Timing

• Happens approximately 6–7 minutes after fire starts.
• Occurs between the “electric and peak stages” (transcription unclear; likely early growth toward peak/fully developed).

Conditions at flashover (as stated)

• Indoor temperature: ~800°F to 100°C
• Oxygen concentration: about 10%

Why it’s especially dangerous

• “Nightmare for firefighters” due to massive heat.
• Severe burns even while wearing fireproof suits.

Factors affecting flashover

• Size of openings
• Composition of interior materials
• Size of the “fire circle”
• Termination state of the object (transcription unclear)
• Interior surface area

How material affects timing

• Combustible materials cause faster flashover than flame-retardant materials.
• Low thermal conductivity interior materials (especially thin ones) are affected faster.
• Ceiling materials ignite/heat sooner than wall materials.

Preventive/support measures (detailed bullet list)

• Use thicker interior materials with high thermal conductivity.
• If possible, make interior materials non-combustible, especially:
  • Ceilings
  • Structural frames
• For openings:
  • Enlarge their size
  • If possible, increase their number
• For combustible materials:
  • Distinguish between:
    • Non-combustible
    • Flame-retardant
  • Reduce the amount of combustible material
  • Store it in dispersed small quantities

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Backdraft / rollover-type phenomenon (battle after/backdraft)

“Battle after” phenomenon (confined-space fire buildup)

• Occurs when fire breaks out in a confined space.
• Due to lack of oxygen:
  • Flames cannot form
  • Only combustible gas accumulates
• If a door is suddenly opened:
  • Fresh air influx triggers explosive combustion
  • Generates a blast/shock wave
• Named warning:
  • Also called “firefighter killer storm” because firefighters have died from the blast.

Smoldering-related precursors

• Preventing/verifying E100 draft is difficult (subtitle likely transcription error).
• Warning signs mentioned:
  • Door handle becomes hot enough to cause burns
  • Smoke rushes into the “gun barrel” (metaphor describing smoke entry/leak behavior)

Related smoldering phenomena

• Smoldering smoke occurrence
• Formation of “fuming” bio-balls (transcription uncertain)
• Collapse of building walls

Smoldering (detailed characterization)

• Definition:

  • A combustion state where material burns without flames, emitting smoke, until it becomes fully visible after a certain time.

  • Smoke exists in liquid and particulate forms.

  • Characteristics listed:
  • Often occurs in indoor spaces with nearly sealed structure
  • Appears mainly in the early stages, but can occur in enclosed spaces and can cause backdraft
  • Slow combustion on residual fire/solid fuels:
    • Requires less air
    • Mentioned as suitable for “mixing” or similar (transcription uncertain)
  • During main fire:
    • The solid surface can explode without flames
    • Produces fumes
    • Temperatures can exceed 1,000°C via self-destruction
  • During smoldering:
    • Primarily produces carbon monoxide
    • Can be fatal to humans

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End-of-lesson review process (as described)

• Learners are prompted to:
  • Write down their own opinion
  • Check the expert’s opinion
• Then take a quiz:
  • 3 questions
  • 2 chances per question
  • Press Start to begin
• Concludes with: “Shall we review what we learned today together?”

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Speakers / sources featured

• No specific individual speakers are identified in the subtitles.
• Music is mentioned, but no composer/artist is identified.
• External/general sources are referenced implicitly (e.g., “recent fires,” a “comparison table,” and “simulation”), but no named sources are provided.