Evaluating
the Workplace - Automatic Fire Detection Systems
Automatic fire detection
systems, when combined with other elements of an emergency
response and evacuation plan, can significantly reduce
property damage, personal injuries, and loss of life from
fire in the workplace. Their main function is to quickly
identify a developing fire and alert building occupants
and emergency response personnel before extensive damage
occurs. Automatic fire detection systems do this by using
electronic sensors to detect the smoke, heat, or flames
from a fire and providing an early warning.
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If
your workplace uses a fire detection system that was designed
and installed to meet the fire protection requirements
of a specific OSHA standard, it must also comply with
the "Fire Detection Systems" standard 1910.164.
This section will help you achieve the maximum benefit
from your fire detection system by addressing the following
issues: |
| Does
the "Fire Detection Systems" standard
apply to me? |
If
an OSHA standard specifically states that
you must install a fire protection system,
then you are required to follow this standard.
For example, if you install an automatic fire
detection system to satisfy the alarm and
signaling requirement of the "Fixed Extinguishing
Systems" standard 1910.160,
then you are also required to comply with
the "Fire Detection Systems" standard
1910.164.
But if you install a system only for insurance
purposes and not to satisfy any OSHA regulation,
you do not need to comply with this standard.
However, employers not required to comply may
find that the standard offers guidance that
may permit them to more effectively protect
employees and property in the event of a fire.
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| How
do fire detectors work? |
| Fire detectors work
by sensing one or more products of fire. The
three most common detectors are: |
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Smoke
Detectors
Smoke
detectors detect the visible or invisible
smoke particles from combustion. The two main
types are ionization detectors and photoelectric
detectors. |
Ionization
Detectors
The
ionization detector contains a small radioactive
source that is used to charge the air inside
a small chamber. The charged air allows a
small current to cross through the chamber
and complete an electrical circuit.
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When smoke
enters the chamber, it shields the radiation,
which stops the current and triggers an alarm.
These detectors respond quickly to very small
smoke particles (even those invisible to the
naked eye) from flaming or very hot fires,
but may respond very slowly to the dense smoke
associated with smoldering or low-temperature
fires.
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Photoelectric
Detectors
In
a photoelectric smoke detector, a light source
and light sensor are arranged so that the
rays from the light source do not hit the
light sensor. When smoke particles enter the
light path, some of the light is scattered
and redirected onto the sensor, causing the
detector to activate an alarm. These detectors
react quickly to visible smoke particles from
smoldering fires, but are less sensitive to
the smaller particles associated with flaming
or very hot fires.
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 Heat
Detectors
Heat
detectors are normally used in dirty environments
or where dense smoke is produced. Heat detectors
may be less sensitive, but are more appropriate
than a smoke detector in these environments.
The most common heat detectors either react
to a broad temperature change or a predetermined
fixed temperature.
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Heat detectors
use a set of temperature-sensitive resistors
called thermistors that decrease in resistance
as the temperature rises. One thermistor is
sealed and protected from the surrounding
temperature while the other is exposed. A
sharp increase in temperature reduces the
resistance in the exposed thermistor, which
allows a large current to activate the detector's
alarm.
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 Flame
Detectors
Flame
detectors are line-of-sight devices that look
for specific types of light (infrared, visible,
ultraviolet) emitted by flames during combustion.
When the detector recognizes this light from
a fire, it sends a signal to activate an alarm.
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| Installation
and restoration |
 For
fire detection devices to give a prompt warning
of a fire, they must be appropriate for the
location you want to protect and approved
by a nationally recognized testing laboratory
such as Underwriters Laboratory (UL) or Factory
Mutual (FM). 1910.164(b)(1)
Detector
selection
Fire
detectors should be selected based on the
burning characteristics of the materials present
and the nature of location they will be used
to protect.
Smoke
detectors
Ionization
or photoelectric
smoke detectors are designed to identify a
fire during its smoldering or early flame
stages and will meet the needs of most areas
containing primarily wood, paper, fabric,
and plastic materials. During combustion,
these materials produce a mixture of smoke
types with detectable levels of both large
and small smoke particles. Smoke detectors
are suitable for:
- Indoor areas with low ceilings such
as offices, closets, and restrooms.
- Areas that are relatively clean with
minimal amounts of dust and dirt.
- Areas that contain solid fuels like
wood, paper, fabric, and plastic materials.
Heat detectors
Heat detectors
are ideal for areas where flammable gasses
and liquids are handled or any area where
a fire will quickly cause a large change in
the surrounding temperature. Heat detectors
are also suitable for:
- Dirty, dusty or smoky environments.
- Indoor areas without winds or drafts
that can prevent heat from reaching the
detector.
- Manufacturing areas where large quantities
of vapors, gases, or fumes may be present.
- Areas where particles of combustion
are normally present, such as in kitchens,
furnace rooms, utility rooms, and garages
or where ovens, burners or vehicle exhaust
gases are present.
Flame detectors
Flame detectors
are best for protecting:
- Areas with high ceilings and open-spaces,
such as warehouses and auditoriums.
- Outdoor or semi-enclosed areas, where
winds or draughts can prevent smoke from
reaching a heat or smoke detector.
- Areas where rapidly developing flaming
fires can occur, such as petrochemical
production, fuel storage areas, paint
shops, and solvent areas.
- Environments that are unsuitable for
other types of detectors.
Protection
of fire detectors
 Fire
detectors that may be exposed to corrosive
environments must be either made or coated
with a non-corrosive material. 1910.164(d)(1)
In order to keep detection equipment operable,
they must be located away from or out of contact
with materials or equipment which may cause
physical damage or be protected by a cage
or metal guard. 1910.164(d)(2)
Detectors that are installed outdoors and
need to be shielded from the weather to work
properly must be protected with a canopy,
hood, or other suitable device.
All detectors must be securely mounted to
a solid surface, such as screwed to a junction
box with a mounting plate or other appropriate
method that prevents them from putting pressure
or stress on attached wires or tubing. 1910.164(d)(3)
Number, location and spacing of detecting
devices
The number, spacing, and location of detectors
must be based on:
- Field experience or testing,
- Engineering surveys,
- The manufacturer's recommendations,
or
- A nationally recognized testing laboratory
listing.
1910.164(f)
General
guidelines for placing fire detectors:
- Put at least one detector in each room,
storage area, and hallway. You may need
more than one detector per room for those
that exceed the manufacturer's spacing
requirements. For example, if your detector
is rated for 30 feet, install detectors
so they are evenly spaced with no more
then 30 feet between detectors.
- Place the detector as close to the center
of the ceiling as possible when only one
detector is required in a room or space.
- Put at least one detector in each closet,
elevator and dumbwaiter shaft, stairwell,
and other enclosed spaces.
- Place a detector at the top of each
flight of stairs.
- Place the detectors in the path of the
air flow toward the return air duct when
air supply or return ducts are present
in a room or space.
- Place all smoke detectors at least three
feet from ceiling fans.
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| Maintenance
and testing |
Over time, dust, dirt, and
other foreign material can build up inside a detector’s
sensing elements, resulting in reduced sensitivity,
which can limit the amount of warning time given
during a fire. Dirty or dusty detectors can also
result in unwanted alarms that can desensitize occupants
to the alarm system or produce more serious behavior
(such as disconnecting the system altogether).
To avoid malfunctions and unwanted alarms and to
make sure your fire detection system will perform
as expected in the event of a fire, you are required
to:
- Operate and maintain your system in a working
condition, making sure it is always turned on,
except during repairs or maintenance. 1910.164(c)(1)
- Test and adjust fire detectors and fire detection
systems often to ensure that they operate correctly
and maintain reliability. 1910.164(c)(2)
Detectors found to be unreliable and/or with
reduced sensitivity must be replaced or cleaned
and recalibrated.
- Assure that pneumatic and hydraulic operated
detection systems installed after January 1,
1981, are equipped with supervised systems.
1910.164(c)(3)
- Have a qualified person service, maintain
and test all fire detection systems, including
cleaning and necessary sensitivity adjustments.
1910.164(c)(4)
- Have fire detectors cleaned on a regular basis
as necessary to assure their proper operation.
1910.164(c)(5)
All fire detection equipment
must be returned to normal operation as soon as
possible after being tested, used, or accidentally
activated. 1910.164(b)(2)
Note: You
are also required to have spare detection devices
and components readily available in the workplace
or from a local supplier to ensure prompt restoration
of the system. |
| Specific
applications or uses |
 The
following applies to fire detection systems used
for specific applications:
- When a fire detection system is installed
for the purpose of activating a fire extinguishing
or suppression system, it must be designed to
respond in time to control or extinguish the
potential fire. 1910.164(e)(1)
- When a fire detection system is installed
as an employee evacuation alarm, it must be
designed and installed to provide a warning
for emergency action and safe escape of employees.
1910.164(e)(2)
- Do not delay alarms or devices actuated by
fire detectors for more than 30 seconds, unless
the delay is necessary for the safety of employees.
For example, if a fire suppression system uses
a compressed gas that will flood an occupied
area, it will be necessary to give employees
time to escape. If such a delay is necessary,
it must be addressed in an emergency
action plan meeting the requirements of
1910.38.
1910.164(e)(3)
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