David
E. Baker and Paul Adams
University of Missouri Extension
Residential
fires have become a significant problem throughout the United
States. The National Fire Protection Association (NFPA) estimates
that residential fires in the United States kill 4,000 - 5,000
persons annually and resulted in injury to 20,000 more.
According
to the Federal Emergency Management Agency, in its National
Fire Incident Reporting System, the leading causes of residential
fires in one- and two-family dwellings were heating (31 percent),
cooking (15 percent) and incendiary or suspicious (10 percent).
In residential
properties, cigarettes are still the leading cause of accidental
multiple death fires (those fires that are fatal to three
or more persons) by a factor of two to one. Fires resulting
from fixed or portable heating equipment - wood stoves, kerosene
heaters, gas or electric cooking stoves, etc. - are the second
most common cause of accidental multiple death fires in residential
properties.
An NFPA
study of 1982 multiple death fires shows that residential
fires accounted for nearly 90 percent of the fires and 85
percent of the deaths. This study also showed that 83 percent
of the fires originated in the living room, 20.8 percent in
the bedroom, 11.7 percent in the kitchen, 7.6 percent at exits,
5.1 percent in a structural area, 1.5 percent in a heating
equipment room, and 3 percent in other areas. About 81 percent
of the multiple death fires occurred between 8 p.m. and 8
a.m. when people are asleep and unaware of the development
of a fire until it is too late.
Fire
officials estimate that at least 50 percent of lives lost
due to residential fires could be saved by installing early
warning fire detection devices and developing and practicing
an evacuation plan.
To protect
the purchaser and establish criteria for the manufacture and
installation of residential fire detection systems, the National
Fire Protection Association has developed NFPA No. 74, Standard
for Household Fire Warning Equipment.
There
are two types of residential fire detection systems: heat
and smoke detectors. The basic residential detection system,
according to NFPA 74, relies primarily on the use of smoke
detectors.
The
standard does not require the use of heat detectors as part
of the basic protection scheme, but it recommends that heat
detectors be used to supplement the basic smoke detector system.
Smoke
detectors consist of a sensing chamber, alarm sounding device
and a means of electrical power transmission. There are two
kinds of residential smoke detectors: ionization and photoelectric.
Ionization.
The ionization smoke detector uses a radioactive source (typically
Americium-241, an alpha-emitting radionuclide) to ionize the
air within the sensing chamber. The ionization of air by the
radioactive particle causes a very small flow of electrical
current. When smoke from a fire enters the chamber, its presence
causes a reduction in the current's flow. The electronic circuitry
senses the reduced flow and triggers the alarm horn (Figure
1).
Photoelectric.
Photoelectric smoke detectors use the principle of scattered
or reflected light to indicate the presence of visual smoke.
They work much like the automatic eyes used to open doors.
When there's no smoke, the chamber is dark. The light shines
across the chamber and is received in a light trap on the
far side. When smoke is present in the chamber, a photocell
located at right angles to the light source senses the light
scattered off the smoke particles and, at a certain level
of illumination, triggers the alarm horn (Figure 2).
Both
detectors sense the presence of smoke. The photoelectric detector
senses the large, visible smoke particles. The ion chamber
detector senses the small, invisible particles.
If a
fire starts and slowly smolders in upholstery without visible
flame, a good photoelectric unit would be superior to a good
ion chamber detector in terms of detection time. But, if the
fire has flames, a good ion chamber will detect it faster
than a good photoelectric detector. For this reason, it's
a good idea to use both types in your detection system.
Combination.
Recently, manufacturers have begun to introduce and market
smoke detectors that combine ionization and photoelectric
sensors in the same unit. These units should combine the advantages
of both sensors into an advanced unit that will detect smoke
from a broader spectrum of fires (smoldering or flaming).
As the demand for these units increases, the cost should decrease
to a competitive level.
Heat
detectors. A residential fire detection system may also
include a heat detector. There are two types of heat detectors:
fixed temperature and rate-of-rise.
Fixed
temperature detectors. These detectors are preset to
sound an alarm when the air temperature exceeds the fixed
temperature. The most popular fixed temperature detectors
used in homes are preset to sound an alarm when the temperature
exceeds 135 degrees F. Other units are available to be preset
up to temperatures of approximately 200 to 225 degrees F.
These detectors may be used in an attic where summer temperatures
normally may reach 135 degrees F.
Rate-of-rise
heat detectors. These sound an alarm when the temperature
in the immediate vicinity rises higher than the preset rate
per time factor (minutes, etc.).
AC-powered
units
NFPA Code No. 74 requires that AC (home current) powered units meet the following conditions:
- Power
supply must be sufficient to operate the alarm signal(s)
of 85 decibels for at least four consecutive minutes.
- A
visible Power On indicator must be provided.
- All
electrical systems designed to be installed by someone other
than a qualified electrician must be powered from a source
not in excess of 30 volts. These systems should meet the
requirements for power-limited fire-protective signaling
circuits as defined in Article 760 of the National Electric
Code No. 70.
- The
power source for the unit must not be subject to loss of
power by a wall switch.
- Neither
loss nor restoration of the primary power should cause an
alarm signal.
- A
restraining means should be used at the plug-in of any cord-
connected installation.
- Single-station
and multiple-station smoke detectors, powered from 120 VAC
sources, should not be installed on circuits protected by
a ground fault circuit interrupter.
Battery-operated
units
NFPA Code No. 74 requires that battery- operated units meet the following requirements:
- The
alarm must be capable of producing an alarm signal of 85
decibels for four consecutive minutes.
- The
batteries must meet all power requirements for at least
one year, including routine testing.
- A
distinctive, audible trouble signal must be given at least
once per minute for seven consecutive days before the batteries
are incapable of operating (from aging, terminal corrosion,
etc.).
- The
unit must also be capable of producing the alarm signal
for four consecutive minutes during the seven days of trouble
signal.
Battery-operated
smoke detectors have two advantages and one disadvantage when
compared with detectors operated from the dwelling's electrical
power. One advantage of battery-powered units is that if the
electrical power in the dwelling should be off due to an interruption
from the utility company or from a fire within the dwelling,
the detector will still function. Some manufacturers are now
manufacturing units with a battery backup in case power is lost.
The
other advantage is that you can install a smoke detector in
an existing dwelling where an appropriately placed electrical
outlet is not available.
The
major disadvantage is that the batteries need to be replaced
once a year.
The basic
(minimal) detection system should consist of one smoke detector
outside of each sleeping area and one additional smoke detector
unit on each additional living level, including the basement
and excluding unfinished attics, crawl spaces, etc. If hallways
are longer than 40 feet between the sleeping and living areas,
use two smoke detectors.
A good
system should include both types of smoke detectors one plug-in
smoke detector and one battery-operated smoke detector. You
might consider installing a photoelectric unit in the bedrooms
of any family members who smoke.
Heat
detectors or additional smoke detectors can supplement the
basic system. Consider these areas for heat detectors: kitchen,
dining room, furnace room, attic, garage or utility room.
Follow
the manufacturer's recommendations for mounting and servicing
the detectors. Place the first unit in the center of the hallway
ceiling between the bedrooms and the living area, not closer
than 12 inches from the wall.
Determine
additional locations according to your lifestyle. If you must
wall-mount the detector, it should be mounted no closer than
6 inches and farther than 12 inches from the ceiling. This
is to avoid the dead air space.
If you
own a mobile home, you may want to consider wall- mounting
your units on an inside wall to avoid some of the problems
of ceiling drafts.
Smoke
detectors should not be located in the following areas:
- Kitchen,
because of false alarms (burned food, etc.).
- Garage,
because of temperature extremes and false alarms.
- In
front of air registers, open windows or open doors, because
of false alarms caused by high air velocities.
- In
or near attics, bathrooms, inside air ducts, unheated buildings,
unheated motor homes, because temperatures may exceed typical
limits of 32 to 100 degrees F.
With
the advent of modern electronic circuitry, the single-station
smoke detector has become the subject of strong sales rivalry
by several companies vying for the household market. The result
is that some sales personnel are using high-pressure tactics.
Therefore, it is wise for the potential buyer of a residential
fire alarm system to be cautious. Here are some buying tips:
- Don't
be frightened into a quick purchase. Some door-to-door sales
personnel use films, pictures and tape recordings that play
on your emotions. Get at least two or three price estimates
from different manufacturers before purchasing.
- Test
the units as you install them or, if you elect to have someone
else install the units, request that the installer test
the units in your presence.
- Request
an instruction booklet that gives you information on operation,
testing and maintenance of the alarms.
- Buy
only fire alarms with labels showing they have passed the
tests of the Underwriters' Laboratories (UL) or Factory
Mutual (FM).
- Understand
the guarantee or warranty with the unit you select, and
be sure you understand who will repair or replace the unit
if it is defective.
Your
job is not done, however, after you buy and install smoke
detectors. There remains the task of training your family
to respond properly when a fire alarm is sounded.
The
first thing to do is to develop a family plan for escape.
It is a good idea to make a floor plan with two escape routes.
Step
A (basic floor layout):
- Make
an outline of the entire floor area. Dimensions and details
need not be exact.
- Now
add each bedroom and label it.
- Locate
windows, doors and stairways. On upper floors, shade in
any rooftops that could be used as a fire escape.
Step
B (room inspection):
- Go
to each bedroom. Select the best window for an emergency
escape.
- Test
the window to see that it works easily and is large and
low enough.
Step
C (complete escape plan):
- Black
arrows show normal exits through hall or stairway.
- Colored
arrows show emergency exits in case fire blocks hallway
or stairs.
Every member
of your family should have at least two escape routes from his
or her bedroom. One usually will be by the door into the hallway;
the other route usually will be by the window.
For
two-story residences, it probably will be necessary to provide
a chain ladder (the first choice) or a rope ladder to escape.
Again, this requires training because the person using the
ladder must make certain he or she is not going to be crawling
past a life- threatening fire on a lower floor and must know
how to use the ladder.
Every
member of your family should know exactly what he or she is
expected to do in the event of a fire. This can be accomplished
by holding family fire drills.
The
first thing to learn is that no one should jump up out of
bed and stand up when the alarm sounds. Instead, all family
members should learn to crawl out of bed onto the floor. In
the early stages of a fire, the toxic and super-heated fire
gases lie in layers near the ceiling. It is very important
to stay below these gases. There have been many cases where
it appears that victims slept through the build-up of deadly
gases only to die when they stood up and inhaled them.
All
members of your family should crawl to their bedroom doors.
If the door is closed, feel it. If it is not hot to the touch,
it is probably safe to place your body weight against the
door and open it slowly to see if smoke and flames have filled
the hallway. Use your body weight to keep the door from opening
quickly in the event that there is heavy smoke or fire in
the hallway or an explosion of fire gases.
If the
hallway appears clear, the first member of the family into
the hallway can then crawl from one bedroom to the next to
make certain that all family members are awake.
Use
the hallway and nearest outside door for escape only if you
are very certain that no flames are visible and there is little
or no smoke along the path you must travel.
Select
a meeting place for all family members outside the home near
the tree, mailbox, etc. Everyone should go immediately to
this meeting place. When everyone is accounted for, someone
can be selected to go to a neighbor's home to call the fire
department.
When
calling the fire department, speak slowly and distinctly so
that you are sure the fire department understands whose house
is on fire and where it is located. In fact, you should practice
giving directions to your home, the same directions you would
give to a visitor who had never been there before.
Stay
outside! Once everyone is out of the house, no one should
return. More than one person has been killed by going back
into a fire to save a few dollars worth of keepsakes.
Obviously,
learning the fire escape plan is like learning anything else
- you get better at doing it if you practice. Periodically,
preferably once a month, someone in the family should sound
the alarm in the middle of the night and then monitor the
actions of other family members to see that they comply with
the fire drill plans.
And
remember installation of an early warning fire alarm system
combined with a well-rehearsed plan for escape may save the
lives of you and your family.
Disclaimer
and Reproduction Information: Information in NASD does not
represent NIOSH policy. Information included in NASD appears
by permission of the author and/or copyright holder. More
NASD Review: 04/2002
This document is
GO1907
,
published by the University Extension, University of Missouri-Columbia,
Columbia, MO 65211. Publication date: October 1993.
David E. Baker, Department of Agricultural Engineering,
and Paul Adams, Director, Missouri Fire and Rescue Training
Institute. University Extension, University of Missouri-Columbia,
Columbia, Missouri 65211.
Issued in furtherance of Cooperative Extension Work Acts
of May 8 and June 30, 1914, in cooperation with the United
States Department of Agriculture. Ronald J. Turner, Interim
Director, Cooperative Extension Service, University of Missouri
and Lincoln University, Columbia, Missouri 65211. An equal
opportunity institution.
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