LIFE SAFETY SYSTEMS IN BUILDINGS: Fire in Buildings

History of Firefighting

The Roman emperor Augustus is credited with instituting a corps of firefighting vigiles (watchmen) in 24 B.C.E. Regulations for checking for and preventing fires were developed. In this era most cities had watchmen who sounded an alarm at signs of fire. The principal piece of firefighting equipment in ancient Rome and into early modern times was the bucket, passed from hand-to-hand to deliver water to the fire. Another important firefighting tool was the ax, used to remove the fuel and prevent the spread of fire as well as to make openings that would allow heat and smoke to escape a burning building. In major blazes, long hooks with ropes were used to pull down buildings in the path of an approaching fire to create firebreaks.

Following the Great Fire of London in 1666, insurance companies formed fire brigades. The government was not involved until 1865, when these brigades became London's Metropolitan Fire Brigade. The first modern standards for the operation of a fire department were not established until 1830, in Edinburgh, Scotland. These standards explained, for the first time, what was expected of a good fire department.

After a major fire in Boston in 1631, the first fire regulation in America was established. In 1648 in New Amsterdam (now New York) fire wardens were appointed, thereby establishing the beginnings of the first public fire department in North America. Up until a hundred years ago, church bells were the only means to alarm citizens of a fire. The most common method of fighting fires after the church bells rang was the bucket brigade: a line of volunteers passing buckets and using water supplies from private wells to quench a fire.

Modern fire departments are a fairly recent phenomenon, developing over the past two centuries. Their personnel are either volunteer (non-salaried) or career (salaried). Typically, volunteer firefighters are found mainly in smaller communities, career firefighters in cities. The modern fire department with salaried personnel and standardized equipment became an integral part of municipal administration only in late 1800s.

Noteworthy Building -- Fire Catastrophes

Several noteworthy fire-related catastrophes have led to sweeping changes in building codes and revised techniques used to prevent and fight fires in buildings. These events include the following catastrophes.

Iroquois Theatre Fire--- On December 30th, 1903, fire broke out at the Iroquois Theater, Chicago, Illinois, when an arc light ignited a velvet curtain. At the time of the fire, approximately 1900 people filled the theater to standing room only capacity. The fire resulted in over 600 deaths and was the deadliest blaze in Chicago history.

When the fire first broke out at the Iroquois Theater, the orchestra continued to play and the audience was told to remain calm and that everything was under control. The fire rapidly erupted into an uncontrolled blaze. Many occupants, still in their seats, died of smoke inhalation. Most occupants made there way to the 27 exits, where they found several of them blocked with wrought iron gates. Some of the gates were locked. Other gates were unlocked but latched and required operation of a latch that was unfamiliar to most theater occupants. Some gates opened inwards. Occupants in front of the unopened gates were trampled and crushed against the doors by a surge of panicking occupants. Trampled bodies were piled ten high in the stairwell area where exits from the balcony met the exit from the main floor. A public inquiry revealed that most in juries occurred within 15 min of the start of the fire, which was put out by the fire department within a half hour. A large fraction of the injuries were caused by being crushed. As a result of these investigations, the fire code was changed to require theater doors to open outward and to have fire exits clearly marked. Theaters were also required to have employees practice fire drills.

Triangle Shirtwaist Company Fire--- On March 25, 1911, a fire broke out at the Triangle Shirtwaist Company factory on the eighth, ninth, and tenth floors of the Asch Building in the lower Manhattan garment district of New York City. Although the fire lasted less than 30 min, 146 of the 500 employees at the factory were killed.

The factory workers, mostly young female immigrants from Europe who worked long hours for low wages, died be cause of inadequate safety precautions and lack of fire escapes.

To keep the employees working at their sewing machines, doors leading to the exits were locked once the workday began.

When the fire rapidly engulfed the factory, panicked workers rushed to the stairs, the freight elevator, and the fire escape. Nearly all workers on the eighth and tenth floors escaped. Most workers on the ninth floor died because they were unable to force open the locked exit door. The rear fire escape collapsed, killing many workers and eliminating an escape route for others still trapped. Several workers tried to slide down elevator cables but lost their grip. Observers of the fire witnessed many frantic leaps by workers from the ninth floor windows. Others were simply burned to death.

The Asch Building itself was constructed of modern construction techniques and was classified as fireproof. An investigation concluded that the fire was caused by combustible shirtwaists and fabric scraps that littered the floors. This tragedy eventually led to the introduction of fire-prevention legislation, factory inspections, liability insurance, and better working conditions for employees.

Coconut Grove Nightclub Fire--- A fire struck the Cocoanut Grove nightclub in Boston, Massachusetts, on November 28, 1942. On the night of the fire, the night club had approximately 1000 occupants, many of whom were military personnel preparing to go overseas for World War II.

Almost half (492) of the occupants were killed, and many more were seriously injured, in less than 10 min.

Combustible contents such as satin drapes, plastic upholstery, and paper decorations spread thick smoke and fire rap idly. One exit door, equipped with panic hardware, was chained shut. The two revolving doors at the main entrance had bodies stacked up to five deep after the fire was brought under control.

Authorities estimated that possibly 300 of those killed could have been saved had the doors swung outward. The "safe" capacity of the structure had also been exceeded.

The Coconut Grove fire prompted major efforts in the field of fire prevention and control for nightclubs and other related places of assembly. Immediate steps were taken to pro vide for emergency lighting and occupant capacity limitations in places of assembly. Exit lights were also mandated as a result of the concern generated by this fire.

World Trade Center Attack---A terrorist attack catastrophically destroyed the twin towers of World Trade Center in New York City. The two towers were un able to endure the effects of a direct hit by two hijacked commercial jetliners on the morning of September 11, 2001.

Shortly after the attack, both towers collapsed, killing nearly 3000 people.

Although the towers were designed to withstand being struck by an aircraft, the resultant explosions and fires weakened the structure of the building, collapsing the upper floors and creating too much load for the lower floors to bear. Once one story collapsed, all floors above began to fall. The huge mass of falling upper structure gained momentum, crushing the structurally intact floors below and resulting in catastrophic failure of the entire structure. This tragedy will unquestionably have a long-term effect on building codes, fire prevention, evacuation plans, and firefighting tactics in skyscrapers. It has resulted in more stringent emergency evacuation procedures and improved safety regulations for all high-rise commercial and residential buildings.

The Station Nightclub Fire--- On February 20, 2003, a one-story nightclub called The Station, in West Warwick, Rhode Island, was engulfed in flames within 3 min after an on-stage pyrotechnics display spread to highly combustible soundproofing foam. This led to 100 fire related deaths and 180 injuries in a few minutes. Fire officials had inspected the nightclub two months prior to the tragedy, as part of a reapplication for a liquor license. After the fire, they reported that no permit had been granted to use the pyrotechnics. Although fire officials reported that the club was below its occupancy limit of 300, films of the event show that the club was crowded at the time of the fire. Eyewitnesses claimed that patrons were late in reacting to the fire because they believed the flames spreading along the walls of the stage were part of the pyrotechnics display. Panic ensued when thick black smoke began spreading across the ceiling.

Although several of the deaths were the result of burns and smoke inhalation, many were determined to have resulted from occupants getting trapped at crowded exits. Computer simulations conducted for a National Institute of Standards and Technology (NIST) investigation concluded that a sprinkler system would have contained the fire enough to give the occupants time to exit the building safely. An automatic fire sprinkler system was not required in the structure because of its age and small size. The concerns that grew from this fire were the lack of automatic sprinkler protection and the use of highly combustible sound-deadening foam. The rapid spread of this fire in this incident makes a case for regulations for automatic sprinkler protection in small commercial and residential buildings.

Fire

Fire is a combustion reaction that requires oxygen (air), heat, and a fuel. Typically, a spark or flame ignites the fire, beginning the combustion reaction. In order for combustion to continue, there must be sufficient heat given off by the reaction and a proper blend of oxygen and fuel. The rate at which a fire burns is dependent on the composition of the fuel, the surface area of the fuel, the rate at which fuel absorbs heat, and the amount of oxygen that is present.

A fuel must be in a gaseous state for combustion to occur. Heat from ignition and later heat generated by the flames of the fire cause solid and liquid fuel to decompose into volatile gases. These volatile gases enter the flame, mix with oxygen in the surrounding air, ignite, burn to create heat, causing more fuel to decompose and make additional gas that enters the flame. This chain reaction continues as long as there is the proper blend of oxygen (air), heat, and a fuel. Combustible gases (e.g., natural gas, propane, and so on) mix easily with air and will burn continuously as long as the proper air-gas blend is present.

Different fuels ignite at different temperatures.

Piloted Ignition Temperature

The piloted ignition temperature of a fuel is the temperature at which a fire can start when a flame or spark begins the combustion reaction. The fuel is hot enough that it releases sufficient flammable gases for combustion to occur, but a catalyst is needed to begin ignition. A large mass requires a greater rate of heating to reach the piloted ignition temperature than a small mass (e.g., igniting a large log opposed to a stick).

Autoignition Temperature

The autoignition temperature, sometimes called the spontaneous ignition temperature, is the lowest temperature at which a combustible material ignites in air without a spark or flame. Some materials do not ignite spontaneously because they break down into other substances at high temperatures and never achieve a spontaneous ignition temperature. Spontaneous combustion often occurs in piles of oily rags, green hay, dust, leaves, or coal; it can constitute a serious fire hazard.

An uncontrolled fire can engulf an enclosed building space very rapidly. A wastepaper basket full of combustible paper can turn into an uncontrolled blaze in less than a minute.

An ignited upholstered chair will fill a room with black smoke in 90 s. Temperatures from combustion of ordinary building materials in an enclosed space can exceed 1200°F (650°C) in a matter of minutes and 1600°F (870°C) in a half hour. Burning flammable liquids (e.g., gasoline, jet fuel, and so forth) can cause temperatures in an enclosed space to exceed 2000°F (1100°C).

Progression of Fire

There are four stages in the progression of a fire: ignition, flame spread, flashover, and consumption. The first stage of any fire begins with the ignition of a fuel source. Ignition re quires the proper blend of oxygen (air), heat, and fuel.

The second stage is flame spread, which is characteristic of rapid crawling tongues of fire that lick across the surface of walls, ceilings, floors and supporting timbers. The nature and combustibility of the material govern the speed and intensity of flame spread.

As the fire intensifies, the heated material releases large volumes of volatile gases into the air. When the mixture of gases and air reach critical proportions, the material ignites in a great ball of fire called the flashover stage. Flashover instantly consumes the surrounding oxygen and can raise the premise temperature to exceed 1500°F (816°C). During the flashover stage, the fire might reach explosive proportions.

The final stage in the burning sequence is the fiery consumption of the material itself as it burns to ash. The rate of destruction depends on the amount of oxygen-rich air reaching the burning area and the combustibility of the fully ignited material.

Classifications of Fires

Generally, fires are classified into four groups by type of fuel:

Group A: Ordinary combustibles (e.g., wood, paper, plastics, trash, grass, and so on) Group B: Flammable liquids (e.g., gasoline, oil, grease, acetone, and so on) Group C: Electrical equipment (e.g., any electrical wiring, connection, equipment, and so on) Group D: combustible metals (e.g., potassium, sodium, aluminum, magnesium, and so on)

Extinguishing a Fire

Building fires typically begin with the ignition of building contents (e.g., a smoldering cigarette sets fire to upholstered chair or mattress). If the flames are not extinguished quickly (while the fire is in the content phase), the fire will expand throughout the structure. Fire will spread throughout concealed spaces and cavities in walls, floors, crawl space, and attic, and eventually to the outside of the building.

Once ignited, fires become self-sustaining as the increase in temperature heats the fuel above its flash point. Fires must be extinguished by eliminating at least one of the constituents in the chemical reaction: fuel, oxygen, or heat energy. Taking away the fuel, cutting the oxygen supply, and lowering the temperature of the burning mass and surroundings are effective methods.

Extinguishing a building fire is more complex than quenching a content fire. The spreading flames that are sometimes concealed must be located and disrupted in addition to extinguishing the original content fire. To accomplish this effectively, the firefighter must know the various ways fire can spread throughout a building structure.

Performance of Materials in a Fire

Building materials exposed to the high temperatures in a fire can fail rapidly. Structural collapse from high temperature is a real safety concern in buildings, as evidenced by the collapse of the World Trade Center towers after the terrorist attacks and resulting fires on September of 11, 2001.

The materials most commonly used in building structure assemblies are steel, wood, brick, and concrete. Their performance in a fire varies significantly:

Steel

Steel is a noncombustible material, yet it displays a significant loss in strength at high temperatures. Structural steel loses about half of its strength at a temperature of about 950°F (510°C). At temperatures of about 1350°F (730°C), steel loses about 90% of its strength. As a result, structural steel is typically protected from fire by an insulating layer of fire-resisting material.

A fire-resisting material limits temperature rise of steel in a fire to keep it from losing strength. Some light materials such as gypsum plaster and wallboard are effective as fire protection of steel. Stronger materials such as concrete or masonry may also contribute to the load-carrying capacity of the assembly, thus extending in some cases the fires endurance.

Lumber and Timber

Wood is a good insulator, but when it is exposed to fire at temperatures as low as 300°F (150°C), it will burn until it is destroyed. In a fire, wood loses strength by charring. The reduction in effective cross-sectional area is dependent on the number of faces exposed to the fire.

The penetration of surface charring of the wood surface in a fire is fairly consistent with time. It is estimated that the depth of char in wood surfaces exposed to the standard en durance test temperature is about 1.5 in (37.5 mm) per hour (about 1/40th of an inch per minute).

Fired Clay Masonry

Brick and other fired clay products are vitrified in a kiln (oven) at high temperatures during their manufacture. As a result, fired clay masonry units are relatively stable in a fire endurance test. Brick also displays reasonably good thermal performance. One of the more significant factors in the fire endurance of hollow brick masonry is the amount of solid material in the wall thickness.

Hollow clay masonry units having thin face shells and webs are subject to stresses resulting from unevenly distributed thermal expansion. The tendency to spalling and shattering has been observed in hollow clay tiles.

Concrete

Concrete, which is similar to brick in thermal performance, loses strength gradually during exposure to high temperatures.

It retains about half its original strength at 950°F (510°C) and one-third of its original strength at about 1300°F (700°C).

This loss in strength is irreversible because it is from the deterioration of the cement binder and, in some cases, degradation of the aggregate.

The fire endurance properties of concrete depend on the type of aggregate, the proportions of the concrete mix, and moisture content at the time of fire exposure. Wide variations in performance are possible. Concretes composed of limestone aggregate display generally favorable performance in fire, whereas some quartz and granite aggregates used in concrete have a tendency to spall when exposed to high temperatures.

There are two factors to be taken into account in assessing the fire endurance of reinforced concrete. One is the thickness of concrete required to limit the temperature rise on the unexposed surface to 250°F for the period desired; the other is the cover required to keep the temperature of the reinforced steel below that at which it will lose its effective strength. Pre-stressed concrete requires greater thickness of cover to the reinforcement than regular reinforced concrete because a lower temperature will release the pre-stress and bring about collapse of the assembly.

Like clay masonry, hollow concrete masonry units (CMU) have face shells and webs that are subject to temperature variations and uneven thermal expansion stresses. With CMU, however, the face shells and webs are thicker and thus the spalling and shattering observed in hollow clay tiles is much less apparent with CMU. Additionally, CMU cells are frequently filled with grout, a cementitious material that in creases the apparent thickness of the concrete, making it per form like a thick concrete member.

With most materials, an assembly of small members ex posed to high temperatures in a fire is more vulnerable than an assembly of large members.

Building Construction Types

There are five fundamental categories of building construction in the United States known as types of building construction, as summarized in Tbl. 1. Each type of building construction has fire-resistive strengths and weaknesses-that is, some types burn much more readily than others. The five building construction types are arranged in the form of a scale based on the amount of combustible material used in their construction. For example, a Type I fire-resistive building has the least amount of combustible material in its structure, whereas a Type V wood frame building has the most combustibles in it.

In addition to the relative combustibility of the materials in the five types of building construction, unique fire spread problems are inherent in each type. These recurring fire spread hazards increase firefighting problems. The following are chronic problems that allow fire to develop in each one of the five basic types of building construction.

Fire-Resistive (Type I) Construction

Fire-resistive (Type I) construction, with its concrete and protected steel walls, floors, and structural framework, was initially intended to confine a fire by its method of construction- that is, by containing the fire with noncombustible wall, ceiling, and floor assemblies so it is confined to one floor or one space on a floor. However, fire does spread several floors in a modem fire-resistive building through two paths: through duct work in the central heating, ventilating, and air conditioning (HVAC) system and by flames extending vertically from window to window.

A system of HVAC ducts can spread fire and smoke throughout a building that is fire-resistive construction. Air ducts delivering air to interior spaces in a central HVAC system go through walls, floors, partitions, and ceilings. They penetrate fire barriers and fire separations. Fire or hot gases in a room near a fresh air intake or return air duct will be sucked into the duct system and be blown throughout the structure if the system continues to operate. Fire can spread to other areas of the building.

Deadly smoke can also be distributed throughout the building.

Therefore, the first action taken in a burning fire-resistive building should be to shut down the HVAC air system.

The vertical spread of flames from windows below to windows above is another way fire spreads throughout a Type I building. Flames erupting out of a heat-shattered window can break or melt glass in a window directly above. Once the window above is open, flames can enter and ignite combustible ceiling tile, wall hangings, or furnishings. Even if the windows do not melt or break from heat, concealed cavities between the exterior wall and the end of the floor slab can allow vertical spread of fire and smoke from floor to floor above and near a window.

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[TABLE 1 TYPES OF BUILDING CONSTRUCTION THAT SERVE AS THE FUNDAMENTAL CATEGORIES OF BUILDING CONSTRUCTION IN THE UNITED STATES.]

Type Category Name Combustibility Description of Structure

I Fire-Resistive II Noncombustible III Ordinary IV Heavy-timber V Wood-frame

Least combustible | Most combustible

Noncombustible wall, ceiling, and floor assemblies; concrete, masonry, and protected steel walls, floors, and structural framework. Roof covering is noncombustible.

Noncombustible steel or concrete walls, floors, and structural framework. Roof covering is combustible.

Noncombustible masonry-bearing walls, but the floors, structural framework, and roof can be made of wood or another combustible material.

Structure consists of large solid wood timbers.

Interior framing and exterior walls are constructed of slender repetitive wood studs, joists, rafters, and trusses that burn very rapidly.

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Noncombustible (Type II) Construction

Noncombustible (Type II) construction is also built of noncombustible steel or concrete walls, floors, and structural frame work; however, the roof covering is combustible, which can burn and spread fire. The roof covering of a Type II building can be constructed of a combustible built-up roof covering, a layered asphalt and felt paper covering, or an ethylene propylene diene monomer (EPDM) or polyvinylchloride (PVC) thermoplastic membrane. Combustible foams may be used as thermal insulation. When a fire occurs inside a Type II building, flames can rise to the underside of the steel roof deck, conduct heat through the metal, and ignite the combustible roof covering. The asphalt, felt paper, and foam insulation may burn and spread fire along the roof covering.

Ordinary (Type III) Construction

Ordinary (Type III) construction is built of noncombustible masonry-bearing walls, but the floors, structural framework, and roof can be made of wood or another combustible material. The major recurring fire spread problem with Type III construction is concealed spaces and penetration. These small voids, cavities, and openings through which smoke and fire can spread are found behind the partition walls, floors, and ceilings. Wood studs, floor joists, and suspended ceilings create concealed spaces. Penetrations are created by small openings for utilities.

These small openings around pipes and wires allow fire to spread into concealed spaces. Flames can spread vertically several stories or horizontally to adjoining occupancies through concealed spaces. Fire spreads inside concealed spaces of a Type III building by convection, the transfer of heat by motion of a liquid or gas. Heated fire gases and flames in a concealed space can travel upwards several floors and break out in an attic space, engulfing the entire building envelope.

Heavy-Timber (Type IV) Construction

Heavy-timber (Type IV) construction is built of a structure that consists of large timbers. In this type of construction, a wood column cannot be less than 8 in thick in any dimension and a wood beam cannot be less than 6 in thick. The floor and roof decking can be thick wood planks. Exposed timber beams, columns, and decks, if ignited in a fire, create large radiated heat waves after the windows break during a blaze. If a fire in a heavy-timber building is not extinguished by the initial fire fighting attack, a tremendous fire with flames shooting out of the windows will spread fire to adjoining buildings by radiated heat. A fully involved type IV building requires large water supply sources to protect nearby buildings.

Wood-Frame (Type V) Construction

Wood-frame (Type V) construction is the most combustible of the five types of building construction. A wood-frame building is the only one of the five types of construction that has combustible exterior walls. The interior framing and exterior walls are typically constructed of slender repetitive wood studs, joists, rafters, and trusses that burn very rapidly. Flames can spread out a window and then along the outside wood walls in addition to the interior fire spread. A Type five building is rapidly en gulfed in flame and is therefore reserved for small structures with small occupancies.

Fire Damage in Buildings

Although heat alone can prove deadly to occupants, toxic gases in smoke cause the majority of deaths and injuries. About half of all fatalities from fires are from carbon monoxide poisoning, and more than a third are from cardiopulmonary complications.

On average, there are about 2.1 million fires reported annually in the United States. Losses from all natural disasters combined (e.g., floods, hurricanes, tornadoes, and earthquakes) average a fraction of the annual direct dollar loss from fire.

Fires in U.S. homes have taken a high toll of life and property each year: over 5000 deaths. Additionally, there are an average of 28,300 reported civilian injuries and an average of 54,500 firefighter injuries annually. Direct property loss from building fires averages about $10 billion dollars every year.

Fire is one of the greatest fears of any homeowner, business owner, or director of an institution. Although the prime concern is always loss of lives in a fire, more than half of all businesses never reopen after the devastating effect of a fire.

The United States has the sixth highest fire death rate among all industrialized countries. According to the National Fire Protection Association (NFPA), 75 to 80% of all deaths by fire happen in dwellings. More than half of these deaths occurred in buildings without smoke alarms. The threat of a fire destroying lives and property can be reduced tremendously by proper installation of fire detection, alarm, and suppression equipment. In residences, automatic sprinkler systems cut the chances of dying in a fire by more than half.

When combined with smoke alarms, they cut the chances of dying in a fire by more than 80%, relative to having neither.

Sprinklers also cut the average property loss in a fire by one half to two-thirds.

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