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FIRE HAZARDOUS - II
METHODS
Since FUEL,
OXYGEN , and IGNITION SOURCE must be present in order to have fire,
one or more of these three elements must be removed or reduced to
extinguish a fire.
Cooling the
Fire
If the heat is
reduced by cooling the substance below the kindling temperature, the
fire goes out. The cooling method is the most common way to put out
a fire. Water is the best cooling agent because it is low in cost
and usually readily available in quantity.
Segregating
the Oxygen
Another method
of extinguishing fire is by eliminating or diluting the oxygen. This
is usually done by smothering or blanketing the fire. Some substance
that is not readily combustible is used to cover the fire. Sand,
foam, steam, or a nonflammable chemical may be employed. A blanket
or rug may be used to cover and smother a small blaze.
Segregating
the Fuel
A third method
is called separation. This method involves removing the fuel, of
combustible material, from a fire. In forest fires, for instance,
the trees may be cut away leaving a fire lane in which the spreading
flame can find no fuel. Explosives may be employed to block oil-well
fires.
FIRE
EXTINGUISHER
Several types of
fire extinguishers have been invented to put out different kinds of
fires. They must be ready for instant use when fire breaks out. Most
portable kinds operate for less than a minute, so they are useful
only on small fires. Instructions on the extinguishers tell how to
use them most effectively. It is important for the user to learn the
properties and proper use of each type for each class of fire. The
law requires ships, trains, intercity buses, and airplanes to carry
extinguishers. They hang in schools, theaters, factories, stores,
and high-rise buildings. Some people keep them in their homes, in
barns, and in automobiles.
The simplest
extinguisher contains water and has a hand pump to throw a stream. A
garden hose can serve the same purpose. A common chemical type is
the soda-acid extinguisher. It contains bicarbonate of soda
dissolved in water and a small container of sulfuric acid. When the
extinguisher is inverted, the chemicals mix and generate carbon
dioxide (CO2). This gas forces the fluid through a hose.
Foam
extinguishers are used in flammable-liquid (Class B) fires as well
as Class A fires. Solutions of sodium bicarbonate and aluminum
sulfate in separate compartments mix when the extinguisher is
inverted. The resulting foamy mixture floats on the burning liquid,
smothering the flames.
A smothering and
cooling extinguisher consists of a steel cylinder of carbon dioxide
under high pressure. When released the heavy gas forms a blanket
over a liquid fire. Continued use prevents reflashing. It is also
used on Class C blazes.
In dry-chemical
extinguishers a cartridge of high-pressure gas is released. It blows
a powdery coating of sodium bicarbonate over flaming liquids,
electrical equipment, or other materials. Vaporizing-liquid
extinguishers contain a fluid which will be vaporized into a
smothering gas by the heat of the fire. Care should be taken not to
breathe the fumes.
Extinguishers
should be inspected and recharged regularly. Reliable ones must have
an attached label, indicating the date of its last inspection.
SPECIAL FIRE
PROBLEMS
Some kinds of
fires create special problems. Such fires require special
fire-fighting techniques and, sometimes, specially trained personnel.
BLEVE (Boiling
Liquid expanding vapor explosion)
Among the most
difficult and dangerous fires are those involving tank vehicles such
as fuel trucks or fixed tanks that contain flammable liquids or
combustible gas. If a tank containing flammable liquid or liquefied
gas ruptures, the fuel can pour onto the ground and a huge mass of
fire may develop almost instantly. However, if the tank does not
leak or rupture and is vented correctly, heat from a fire should
cause the gas to be released and burn at the tank vent. If this
happens, water streams may be applied safely.
Tanks on trucks
or ground supports, if exposed to a ground fire, may weaken at a
seam or some damaged point. When this occurs, the tank or tank
vehicle can rocket for hundreds of feet, spilling its flaming
contents and endangering all persons in the vicinity.
The worst kind
of explosion that can occur in such tanks is called a BLEVE, an
acronym for "boiling liquid expanding vapor explosion."
BLEVE incidents
are rare, but they occur. They happen when a tank of flammable
liquid is heated to the boiling temperature of the liquid. If flame
from an exterior fire is in contact with the tank shell in the vapor
space above the liquid level and the shell weakens, the consequent
explosion can send fragments of the tank in all directions for about
4,000 feet (1,200 meters). If such an incident is likely, the public
must be kept at least that distance from the tank
Industrial
Fires
Throughout the
world, corporations and businesses have trained fire brigades to
protect life and property. They often are exposed to hazards unique
to an industry, and its members need special training for fire
problems that are common in an industry's particular environment.
Fire problems
vary according to the type of hazards, processes, structures, and
conditions of plant fire fighting equipments and organization.
Today there are
a large variety of equipments to be used in industries like:water
and foam sprinkler systems, dry chemicals and carbon dioxide,
high-expansion foam, halogenated agents, aqueous film-forming foam,
inert gas, and explosion-suppression systems. There may be monitor
nozzles, fire doors and barriers, compartments, and other devices
that function automatically when fire occurs. Some industrial plants
develop color coding and other marking systems that indicate
hazardous areas where sensitive materials are produced, handled, and
stored.
Hotels and
Nightclub Fires
The intimate
atmosphere and elaborate decor that make nightclubs so cozy are also
the elements that can turn them into death chambers when fire breaks
out. Exit routes are usually limited, and panicky patrons are easily
trapped between revolving doors.
Smoking and the
use of unsafe electrical apparatus in hotels plus the lack of
familiarization with building limitations, makes hotel fires very
common .
The huge Beverly
Hills Supper Club in Southgate, Ky., lacked adequate safety devices,
and 165 died when fire spread through its complex of entertainment
rooms in 1977. In 1990 a flash fire in New York City's illegal Happy
Land Social Club killed 87 mainly Central American immigrants who
died within seconds from smoke inhalation.
One of the
biggest and most luxurious hotels on the Las Vegas Strip, the MGM
Grand was badly burned and 84 died there in 1980. There were 97
deaths in San Juan's 22-story Dupont Plaza Hotel in 1986.
High-Rise
Fires
The term
high-rise in fire protection terminology describes a building that
is too tall for adequate fire control from ground-based aerial
ladders or elevating platforms or towers. Because such apparatuses
usually have an effective height of 30 meters or less, a high-rise
building is any taller structure above eight floors. Such buildings
require automatic fire protection and special arrangements for
people to escape.
Some tragic incidents
have occurred in high-rise buildings.
The fire in the 26-story
Andraus Building in Sao Paulo, Brazil, in February 1972 killed 16
people and injured more than 375. Helicopters were used to rescue
hundreds from the rooftop. They were needed again two years later,
when another high-rise in that city had a fire, but others were
trapped in smoke-filled interior stairways.
High-rise fires
have occurred in many other cities, but most of the fire problems
are being solved by modern technology. Smoke is controlled by
automatic shutdown of the air-cooling or ventilating system or by
pressurized air in an automatic system. Fire codes require the use
of fire-resistant materials; certain arrangements of rooms, doors,
corridors, and other means of escape; enclosed stair towers; a means
for fire fighters to override automatic controls of elevators;
automatic fire detection, alarm, and extinguishing equipment; and a
computerized console on a lower floor for monitoring every floor and
room in the building. Not all high-rise buildings have such
protection, even though experience has shown that people can be
trapped when fire develops in such buildings. If time does not
permit rescues by the fire department, the casualties in an
unprotected high-rise building can be numerous.
Hospital
Fires
In the past
hospitals experienced many fires mainly due to the type of
construction, accumulation of combustible materials, open stairways
and corridors, inadequate electrical equipment, improper storage of
combustible gases in or near operating rooms where there were
sources of ignition and lack of qualified people to fight fires.
Today many
hospitals have modern fire protection systems and training programs
through which all employees know their responsibilities if fire
occurs. The fire hazards of operating rooms have been reduced by
changes in anesthetic gases and by removal of spark-producing
equipment and materials. Combustible materials are minimized on
ceilings and walls; corridors are divided by fire-resistant doors;
automatic fire detection equipment monitors rooms and areas on all
floors; exits are clearly identified by signs and arrows; and
automatic extinguishing systems protect the hazardous areas. The use
of smoking materials is forbidden or confined to certain locations.
Hospital personnel are trained in the use of portable fire
extinguishers and in the methods of evacuating patients and visitors
from the building.
Despite these
advances, many hospitals are still susceptible to fires and no
special attention is given to prevent fires and even to combat a
fire
Smoke is a
particularly important factor to consider in hospital fire safety.
Rugs, draperies, and furniture upholstery that are made of synthetic
materials produce dark smoke and toxic gases that are a threat to
any unprotected person. If a fire in a hospital generates smoke but
is confined to an area where it can be extinguished quickly, it may
be practical to close doors of patients' rooms to permit the
ventilation system to clear the atmosphere.
Fire in Mall
and Shopping Centers
In 1995 the
building of a Shopping center in the city o Osasco Brazil, collapsed
due to fire and explosion caused by a leakage of LPG. Several people
were killed and many injured or incapacitated for the rest of their
life.
Shopping center is a
place visited each day by hundreds of people and sometimes the
fashion of the stores hide the reality of the back store, electrical
circuit overload, fire extinguishers damaged, locked emergency exits,
undersigned buildings, lack of safety precautions in the project,
lack of a trained fire brigade.
Arson
From the
beginning of recorded history, the crime of arson has been committed
in almost every society, from the smallest tribe to the largest
modern metropolis. The legal definition of arson varies in different
states and countries, but in simple terms it can be defined as the
act of intentionally burning property in order to cause destruction
or harm. It is a crime that occurs in all types of communities and
in rural and forested areas. The worst effects of arson are the loss
of human life and the pain and suffering of persons who are trapped
in such fires.
The usual targets for
such intentional fires are stores, apartment buildings,
manufacturing plants, schools, and forest.
There are many reasons
why people commit arson, but even though reasons are known, it is
not easy to prevent or even reduce the incidence of this crime. In
most countries, the law enforcement authorities and the fire service
combine their efforts to identify the causes of fires and to arrest
and prosecute arsonists. Another means of fighting arson is through
the installation of modern fire protection equipment and security
measures.
PREVENTIVE
TECHNOLOGY
Increased scientific
knowledge about the nature of fires now permits accurate computer
simulation of the progress of a fire in a particular site. Computer
simulation can also measure the effectiveness of such preventive
devices as smoke detectors, sprinklers, and fire-resistant
materials. The period before a fire within a room "flashes
over"--that is, grows from a small fire into one where the entire
room is ablaze--may be only a few minutes. A simulation can predict
whether a single smoke detector, for example, is sufficient to give
ample warning, and it can demonstrate the most efficient escape
routes.
The most
effective means of controlling fire in large buildings are automatic
fire sprinkler systems. Water pipes are positioned behind the
ceilings; at intervals, sprinkler heads protrude into the room.
Sufficient heat destroys the seals in the sprinklers, releasing a
steady stream of water. The newest sprinklers have automatic shutoff
valves and may be equipped to transmit fire alarms to local fire
departments.
Flame
Retardants
A flame retardant is a
chemical applied to a combustible material to reduce the rate at
which it burns. There are two classes of flame retardants: those
that are most effective for materials containing a substantial
amount of oxygen--such as cellulose and certain synthetic
polymers--and that carry out their function primarily in the
material itself; and those that are effective for materials with
all-carbon structures and little oxygen--polymers such as
polyethylene or polyvinyl chloride--and that work in the burning
vapor above the polymer.
Compounds of
phosphoric acid or of sulfuric acid are most frequently used as
flame retardants for the first class of materials. As long as the
wood, paper, or polymer is in normal use, the acid is neutralized by
a fugitive species, a simple organic substance that vaporizes at the
onset of fire, leaving behind the relatively nonvolatile acid
fragments. On heating, these acids react with the cellulose or
synthetic polymer to produce large amounts of carbon char and
incombustible gases such as steam and carbon dioxide, which either
prevent the fire from starting or smother it. Other simple inorganic
materials, such as borax, zinc borate, and boric acid, are also
effective in retarding flames. They melt at low temperatures and
block diffusion of oxygen to the burning surface.
The second class of
flame retardants work by decomposing in fire to produce volatile
fragments that intervene in the chemical processes in the burning
vapor above the polymer and thereby block the combustion process.
The chemicals most frequently used include bromine compounds and
antimony oxide.
Some fire
retardants may themselves produce fairly toxic gases during exposure
of the treated material to fire temperatures. If a fire is hot
enough to release all of the retardant, the gases may present
problems, particularly for fire fighters.
Alarm Systems
Alarm systems are
designed to detect undesirable events--the start of a fire, a
burglary, a hazardous change in temperature or pressure--and to
issue an alerting signal that will cause corrective action to be
taken. Such systems must incorporate a detector, which is designed
to sense a particular problem, and an alerting agent, such as a bell
or a signal light.
Detectors are sensor
mechanisms that respond to changes in such factors as light, sound
level, pressure, and temperature. Burglar-alarm systems employ many
of the types of detectors in current use. Such systems may utilize
electric detectors, circuits whose contacts open when a door or
window is opened, triggering an alarm. Electric circuits may also be
built into walls to signal if the wall is damaged. Optical detectors
use photosensitive elements that are triggered when a light ray or
infrared beam is interrupted by an intruder. When the light beam is
amplified with mirrors, large areas can be monitored. Acoustic
detectors may be highly sensitive microphones that detect the
smallest noise in a room, or ultrasonic detectors that constantly
transmit an acoustic signal of a frequency that cannot usually be
heard by human ears. An intruder's movements disturb the signal and
set off an alarm. Other types of detectors utilize electronic,
thermal, microwave, or laser devices.
Systems designed
for FIRE PREVENTION AND CONTROL use SMOKE DETECTORS or heat
detectors.
Smoke
Detector
Used for FIRE
PREVENTION AND CONTROL, a smoke detector is a small device designed
to emit an audible warning at the first sign of smoke. The two
principal types are photoelectric, or optical, and ionization.
Photoelectric detectors are activated when smoke obscures or
scatters a beam of light, causing a change in the flow of electrical
current (see PHOTOELECTRIC CELL). Ionization devices are activated
when smoke particles attach themselves to ions created in the
detector by a minute radioactive source, thus reducing the flow of
current. Each type of detector can be powered by house current or
batteries.
Detectors are most
effective when installed on the ceiling or high on a wall, away from
air vents. In the home primary locations should be just outside each
bedroom area; detectors also should be placed on each additional
story and in the basement.
COMMON SENSE
PRECAUTIONS TO WORK WITH FIRE
Respect, not
fear or contempt, is the major safe way to deal with fire.
Before put fuel,
oxygen and ignition source into contact, make sure that there is not
an alternative option.
Always limit the
amount of fuel for the specific use.
Keep all the
time the control of the ignition source.
Never work with
fire without the control of fuel feeding.
Never start fire
equipment in confined ambient.
Use protective
safety devices( gloves, jackets etc. )
Use the proper
method - do not take short cuts when dealing with fire.
Keep your mind
on the work - do not start a fire equipment and forget.
Check the
availability and the conditions of extinguishers, exit routes etc.
Get complete and
proper instructions- learn exactly what you must do, especially when
starting a new source of fire.
Never allow
unqualified people to start fire sources.
Remember that a simple
and small oven has the potential to burn down a house, if operated
without knowledge.
SOURCES OF
INFORMATION
Several organizations
provide information on fire fighting, fire protection, and related
subjects. The National Fire Protection Association, Batterymarch
Park, Quincy, Mass., 02269, develops technical standards on fire
protection, codes, guides, handbooks, motion pictures and other
visual aids, training materials, and programs of public education.
The United States Fire Administration (USFA), Federal Emergency
Management Agency (FEMA), 500 C Street, S.W., Washington, D.C.,
20472, develops fire service education and training programs, has a
National Fire Academy in Emmitsburg, Md., and a National Fire Data
Center through which it conducts research on fire-fighter and
residential safety. The Society of Fire Protection Engineers (SFPE),
60 Batterymarch Street, Boston, Mass., 02110, is a professional
society with chapters in the United States, Canada, Europe, and
Australia. It serves as a clearinghouse of information
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