Fire Alarm Flashcards
what are the basic components of a fire alarm system?
- Initiating Device
- Alarm/Signalling device
- Control Panel (Fire Alarm control unit)
List some examples of Initiating devices
- Smoke detectors
- Heat detectors
- Pull stations
- Flame detectors
List some examples of signalling devices.
- Bells
- Horns
- Strobes
What does the FACU contain?
Power supply and circuitry for operating, monitoring and troubleshooting
What is the Annunciator Panel and where is it typically located?
It is a monitoring panel to indicate the location or zone of the fire or trouble. Usually at main entrance and is graphical
List some examples of Ancillary devices.
- Fan shutdowns
- Fan start-ups
- Fire door magnets
- Door lock releases
- Elevator homing
- Plenum dampers
- Fire phones
- City tie module (CTM)
How does simplex communication work?
One way only
How does Half duplex communication work?
Both ways but only one at a time
How does full duplex communication work?
Both ways at the same time
How does a single stage system work?
any initiating device will cause all signalling devices to be activated
Where are single stage system recommended to be used?
- Schools
- Apartments
- Warehouses
- Industrial Plants
How does a two stage system work?
Any initiating device will first activate an alert signal for 2 - 5 - 15 mins and if not responded to then a general alarm will sound
Where are two stage systems used?
- Hospitals
- Rest homes
- Hotels
- Department stores
- AIrports
What is the alert signal for in a two stage system?
It is for designated persons who may activate the general alarm when they deem necessary. allows supervisory staff to investigate and plan for an orderly evacuation.
What is required for a two stage system?
Trained personal 24 hours/day
How long is the first alert signal? How long is the full alarm?
First alert = 20 bell strokes/min
Full alarm = 120 bell strokes/min
Where are usually all two stage and some single stage systems linked to?
the fire department for a faster response
What is a zone in buildings FA system?
- Defined location that is covered by initiating devices on one circuit (non addressable)
- Defined area with assigned initiating devices (addressable)
What typically determines the number of zones?
size of the building
How many zones do hospitals have?
100+
How many zones do nursing homes have?
2 per floor
What is A.H.J. ?
Authority having Jurisdiction
How do Pull stations work?
- Use a normally open single pole switch operated by a pull handle
- Glass or brittle plastic rod is used to indicated which station has been pulled
How do two stage pull stations work?
- Have a key operated switch along with the handle
- Handle initiates the alert
- Key switch initiates the alarm
Where are pull stations only key operated?
- Mental health facilities
What are the types of heat detectors?
- Fixed temp.
- Restorable or Unrestorable
What are common temps of fixed temp. detectors?
- 58 degrees C/135 degrees F
- 90 degrees C/194 degrees F
How does a restorable type heat detector work?
- Bimetallic strip causes contact closure when it bends due to temp. rise
- When temp. falls, contact opens
How does a non-restorable heat detector work?
- Heat causes solder pot to melt causing a spring loaded set of contacts to close
- No means to reset when temp. falls
- Center red disk indicates tripped
How do rate of rise detectors work? How is the response time compared to Fix detectors?
- Designed to operate any time the temp. of ambient air rises more than 9 degrees C/14 degrees F per minute
- Provide a faster response time than fixed detectors
- Not suitable in areas which see rapid temp. changes
What is a Combination heat detector?
Dual action combining fixed and rate of rise
How does a Line type heat detector work?
- Not a “spot type” device
- Heat sensitive polymer melts and shorts two conductors or a thermistor core conducts
What does a Line type heat detector protect?
Protects long areas such as:
- cable trays
- floating roofs of fuel tanks
- suppression usually accompanies alarm
Where should heat detectors only be used? Why?
- Where property protection alone is required
What are some characteristics of heat detectors?
- Not a life safety device
- mount in the ceiling
- elevator shafts
- Heat detectors on FA system in units, smokies in common halls
What provides the earliest warning of a fire condition?
Smoke Detectors
What are the main types of smoke detectors?
- Photoelectric detector
- Ionization type AKA “product of combustion”
- Beam type
- UV/IR (Fire Eyes) Detector
What do photoelectric detectors use and require?
- Use a light source and light detector
- Require visible smoke to operate
What do photoelectric detectors detect?
2nd stage of a fire (smouldering)
How do photoelectric detectors work? where are they installed?
- Smoke entering chamber affects beam of light cause a n.o. contact to close
- Installed in bedrooms & hallways
What are the two types of Photoelectric detectors? which is best and why?
- Light scattering
2. Light obscuration (best, fail safe)
What do Ionization detectors detect?
1st stage of a fire (incipient)
How do Ionization detectors work?
- Very sensitive, can be triggered by invisible smoke
- Small amount of radio active material between 2 plates
- If particles of invisible or visible smoke enter the chamber current flow is interrupted cause n.o. contacts to close
Under normal operation, what flows in Ionization detectors and how much of it?
- ionization current
- 1 x 10 to the -12 amps
Where should ionization detectors not be used? What may activate them?
- Areas of high humidity, dust or vapours
- Garages
- Air pollution and fog may activate them
What can some ionization detectors be tested with?
a magnet
Where are beam type detectors used?
- Very long and tall rooms where smoke may not reach ceiling due to stratification
How do beam type detectors work? What are the two ways of wiring them?
- Transmit light across room to detect smoke
- Reflective type has wiring at only one end (not good for narrow spaces less than 1 m away from trusses, etc..
- End to end needs wiring to transmitter and receiver (better for narrow spaces)
What do UV/IR detectors detect?
- Stage 3 detector (flame stage)
What usually accompanies UV/IR detectors?
suppression
What are UV/IR detectors best at detecting?
- Flammable liquid fires
- UV detects natural gas, butane, propane (blue flames)
- IR detects gasoline, jet fuel, and diesel (red flames)
List some things signalling detectors can be represented as?
- Audible
- Visual
- Odour based
- Mechanical
List some vibrating bell properties
- Sizes = 4”, 6”, 8”, 10” (most common)
- Sound level proportional to diameter
- Usually 24Vdc or could be 120Vac
- Uses solenoid and plunger to strike a bell
What current does the FA control unit use?
40 mA thru a closed loop
What are some Class A circuit properties?
- Wiring starts and ends at the panel
- Requires twice as much wiring as Class B
- Will still function if an open occurs in a conductor
What are some properties of a Class B circuit?
- Wiring starts at panel and ends at the E.O.L
- E.O.L. values differ between initiating and signalling zones and between manufacturers
What are Class C circuits?
Ancillary
What are some properties of Signalling Circuits? What does each device incorperate? What voltage do they operate on?
- Typically operate on 24Vdc
- Each signally device incorperates a diode which blocks supervisory current when not an alarm
- If panel goes to alarm, zone polarity is reversed on signalling circuits by the panel putting the devices into action
What is the transition stage between stages 2 and 3 called?
Flashover - happens very fast
What 4 basic conditions must there be for a fire to start?
- fuel
- heat
- oxygen
- chain reaction
What is a Class A fire?
ordinary combustibles such as wood, paper, etc..
What is a Class B fire?
flammable or combustible vapours such as gas
What is a Class C fire?
electrical fires
what is a class D fire?
combustible metals such as magnesium
What does PASS stand for a fire extinguisher?
- Pull
- Aim
- Squeeze
- Sweep
What is a type 1 FA system?
1-stage, Non indicating, non-zoned, general alarm
what is a type 2 FA system?
1-stage, Indicating, Zoned, General alarm
what is a type 3 FA system?
1-stage, indicating, zoned, coded, general alarm
what is a type 4 FA system?
2-stage, indicating, zoned, alert/alarm
what is a type 5 FA system?
2-stage, indicating, zoned, coded, alert/alarm
How are addressable system controlled?
microprocessors
How are field devices supervised?
digitally
What does the processor do in addressable systems?
Polls each device with its own unique digital/binary address
Manufacturers systems are _________?
Proprietary (top secret)
Why does the CPU poll each device?
For its state of health (if its okay, in trouble, or in alarm)
What happens if the CPU does not get a response?
it goes into trouble condition
How are device addresses assigned?
- dip switches or rotary dials
- with a laptop via control panel
- automatically by the FACU
- one by one with portable handheld program
how often is each device polled?
at least once per second
What wiring may addressable systems require?
twisted shielded wiring for the devices
What may some devices require in an addressable system?
external power
What are fire alarm isolators?
they remove sections of zones in event of failure so remaining zones can still function
What are the 4 types of sprinkler system? which has the fastest response time?
- Wet-pipe (fastest)
- Dry-pipe
- Pre-action
- Deluge
Where are wet-pipe systems used?
ordinary combustibles where freezing is no worry
schools, hospitals, offices
What do Jockey pumps do? What do they reduce?
Boost water pressure on sprinkler side of the check valve. Reduces false alarms cause by water hammering
Where are dry-pipe systems used? What do the pipes contain?
ordinary combustibles where freezing is a problem
(parkades, warehouses, unheated structures)
Pipes contain air or nitrogen
How much surface area does the dry side have compared to the wet side of a dry pipe system?
3-5 times the surface area
What is a Pre-Action system?
a dry-pipe system where the water is held back by an electronically controlled valve connected to the FACU
When will water enter the system pipes in a pre-action system? how is each head activated?
Only after the fire detection system is activated. Each head is activated individually
Where are Pre-Action systems good for?
where accidental discharge of sprinklers would cause extensive damage (data centers, libraries)
How can you describe the operation of a Pre-Action system?
Double interlocked
- broken sprinkler head
- IDC activation
What are Deluge systems designed for?
High hazard areas
How do deluge systems work?
Pipes are dry and unpressurized with heads open, connected to a water source being held back by a valve
What happens when a Deluge system detects a fire? What agents do they use?
water is pumped thru the pipes and discharged thru the open heads. Majority use foam-based agents.
What are the range of heights permitted for a pull station?
1.05 to 1.15 m
what is the minimum height permitted for a fire bell?
1.8 m to center
max height for an annunciator?
2.4m
max height for a control panel?
2.4 m
max height for an E.O.L.?
1.8 m to top
what is the NBC?
national building code
what is the ULC? what must all FA devices carry?
Underwriters Laboratories of Canada
ULC sticker
what is the NFC?
national fire code
who has the final say in the installation of a FA system?
fire marshall
what is the regulatory body that determines which buildings require FA systems?
National building code
what is the maximum height of audible signal appliances?
manufacturers recommendation
where are E.O.L.’s usually located
beyond the last initiating or signalling device
What is an ancillary device?
device actuated by the FA system but is not required to be part of the FA system
What is electrical supervision?
a means whereby a fault condition that would interfere with the operation of a circuit is detected
what is an annunciator?
device to visually indicate a signal received from the system
give 3 examples of a “zone”
- electrical room
- north stairwell
- second floor
What is a method of psychological deterrent used to discourage tampering with a pull station?
- Mirror
- Ink spray
What is a method of testing a self-restoring type of thermal detector?
place approved heat source next to it
What two possibilities may exist in an initiating cct when an ohmmeter reads a short (approx 0) ?
device tripped, conductors shorted
where are single stroke bells most commonly utilized?
where key personal can hear
what type of battery is used as a standby power supply?
rechargeable (gel-cell)
what is the purpose of an E.O.L. ?
to permit supervisory current to flow
