Fire Safety: Components, Phases, and Construction Types

Fire triangle components

Oxygen, fuel, and heat.

How do you extinguish the basic fire triangle?

Remove one side—oxygen, fuel, or heat—and the fire goes out.

Chemical chain reaction

A chemical chain reaction must occur for a fire to develop; failure to interrupt it allows fire growth.

Direct contact

A method of fire spread where fire directly contacts combustible material.

Conduction

Heat transmitted through a heat conductor, such as metal.

Convection

Heat travels vertically until it reaches a barrier, then moves horizontally.

Radiation

Heat travels through electromagnetic waves until something absorbs it.

Four phases of fire

Ignition → Growth → Fully Developed/Free Burning → Decay/Smoldering.

Ignition phase

First phase of a fire.

Growth phase

Second phase of a fire.

Fully Developed/Free Burning phase

Third phase of a fire.

Decay/Smoldering phase

Final phase of a fire.

Ignition Temperature

Lowest temperature at which a substance catches fire when a heat source is present.

Flash Point

Temperature at which a substance ignites but does not continue to burn.

Burning Point

Temperature at which a substance ignites and continues to burn.

Auto-Ignition Temperature

Temperature at which a substance catches fire without a heat source.

Flammability/Explosive Range

Range of concentration of a flammable vapor or gas in air.

Spontaneous Heating

Heat generated by a material, such as oily rags, faster than the heat can dissipate, potentially causing ignition.

Flashover

Near-simultaneous ignition of all combustible material within an enclosed area.

Backdraft

Explosion after oxygen is introduced into a high-heat, high-fuel, low-oxygen enclosed environment.

Smoke Explosion

Explosion of unburned gases in either an enclosed or unenclosed environment.

Average construction fires per year, 2017-2021

Approximately 4,440 fires in structures under construction per year.

Annual civilian deaths from construction fires

Average of 5 per year.

Annual civilian injuries from construction fires

Average of 59 per year.

Annual direct property damage from construction fires

Approximately $370 million per year.

Construction fires as % of all structure fires

About 1%.

Construction fires as % of direct property damage

About 3%.

Property type with most construction fires

Residential: 76% of fires.

Residential share of construction-fire civilian injuries

76%.

Residential share of construction-fire direct property damage

79%.

Time period with the most construction fires

Noon-6 PM: 31%.

Time period with the most civilian injuries

Noon-6 PM: 42%.

Time period with the most direct property damage

Midnight-6 AM: 51%.

Ignition factor responsible for 44% of direct property damage in the chart

Mechanical failure/malfunction.

Heat source associated with 30% of civilian injuries in the chart

Radiated/conducted heat from operating equipment.

Type I Construction

Fire Resistive.

Type II Construction

Non-combustible.

Type III Construction

Ordinary.

Type IV Construction

Heavy Timber.

Type V Construction

Wood Frame.

Fire spread potential from smallest to greatest

Type I → Type II → Type III → Type IV → Type V.

Construction type with smallest fire spread potential

Type I Fire Resistive.

Construction type with greatest fire spread potential

Type V Wood Frame.

Collapse potential from smallest to greatest

Type I → Type IV → Type V → Type III → Type II.

Construction type with smallest collapse potential

Type I Fire Resistive.

Construction type with greatest collapse potential

Type II Noncombustible.

Designed Load

A load that is anticipated and designed for.

Undesigned Load

A load that is unanticipated.

Concentrated Load

A load applied to a small area.

Distributed Load

A load equally dispersed over a large area.

Dead Load

Weight of the building and anything permanently attached or built into it.

Live Load

Any load that is not built in.

Impact Load

A load in motion.

Static Load

A force with constant size, position, and direction within a structure.

Axial Load

A load that passes through the center of mass of the supporting elements.

Eccentric Load

A load that does not pass through the center of mass.

Torsional Load

A load parallel to a structural member that does not pass through its long axis.

Environmental loads

Wind load, snow load, seismic forces, and gravity.

Fire Load

How much combustible material is in a building and how well it will burn.

What makes up fire load?

All combustible parts and contents of a building.

Why has fire-loading increased?

Increased use of plastics, synthetics, petrochemical-based contents, and treated fabrics.

Effect of modern fire-loading materials

They accelerate fire growth and fire spread.

Compression

A force that tends to push or squeeze material together.

Tension

A force that tends to pull material apart.

Shear

A force that tends to break material by causing its molecules to slide past each other.

Torsion

A force that twists a material.

Bending

A force that pushes on a material.

Brittle Materials

Materials weak in tension and shear that tend to break without bending.

Examples of brittle materials

Concrete, glass, tile, and stone.

Ductile Materials

Materials that tend to deform before breaking.

Examples of ductile materials

Steel, copper, and brass.

Fire effects on concrete

Spalling, external cracking, reduced strength, and a pathway for direct heat to exposed reinforcing steel/rebar.

Steel at 1100°F

Approximately 50% strength reduction.

Steel at 2700°F

Melts.

Steel buckling

Buckling can occur at temperatures as low as 250°F.

Other fire effects on steel

Deformation, oxidation, and permanent structural change.

Fire effects on wood

Strength reduction, inability to support loads, thermal degradation, charring, increased fuel load, and drying out of the wood.

Fire effects on masonry/clay/brick

Dehydration, reduced strength, aggregate changes, and expansion.

Glass at 250°F

Can shatter.

Fire crazing / glass spalling

Rapid cooling can create small, closely spaced cracks.

Other fire effects on glass

Breaking, staining, rib marking, baked-on color, and close-formed curves.

Fire effects on drywall/gypsum

Loss of strength, loss of stiffness, dehydration, charring, expansion, buckling, warping, and cracks/gaps.

Major impacts of a construction fire

Damage assessment, cleanup/debris removal, structural repairs/replacement, electrical and plumbing inspections, insurance claims, investigation/safety measures, and project delays.