Fire Detection and Alarm Systems

Question 1

Most fires develop through four distinct stages, what are these four stages?

Answer 1

1. Incipient Stage - there are no obvious signs of fire at this stage, but thermal decomposition may be releasing tiny combustion particles that are invisible to the eye but detectable with specialized detectors
2. Smoke Stage - visible smoke can be seen, combustion now increases the size and output of particles, but there is still no appreciable heat rise
3. Flame Stage - visible flames can be seen as the gases and particles ignite, the outburst of flames produces heat and great quantities of combustible gases are created
4. High Heat Stage - flames are at their peak, dense smoke is present, oxygen is being rapidly consumed and superheated gases are generated

Question 2

Of the four stages of a fire, what causes the majority of fire-related deaths?

Answer 2

• Smoke, it contains toxic and deadly gases such as carbon monoxide, nitrogen oxides, sulphur dioxide and ammonia

Question 3

A basic fire alarm system must contain at least three componets, what are they?

Answer 3

1. A fire alarm control unit to provide the logic processing system
2. A manual pull station
3. An audible signal device to alert all the occupants of a building that they must evacuate

Question 4

Describe the process of a basic fire alarm system

Answer 4

• The control unit receives a signal from the manual pull station
• The control unit processes this signal and activates the audible signal device

Question 5

What are the four conditions of a fire alarm system?

Answer 5

1. Normal Condition - system is powered and ready to receive input signals from the detection device
2. Trouble Condition - equipment failure, circuit failure or fault is indicated at the control panel or a more suitable location in the building
3. Alarm Condition - the signaling devices activate and warn the occupants to evacuate
4. Supervisory Condition - a change in condition of a field device in an automatic sprinkler system that could prevent proper operation of the sprinkler system

Question 6

What are the two types of fire alarm control units?

Answer 6

1. Single-Stage System - an audible evacuation alarm is sounded immediately by all signal devices or appliances when an automatic fire detector or manual pull station is activated
2. Two-Stage System - when an automatic fire detector or manual pull station is activated, an audible alert signal is sounded and trained personenel respond to the alert signal and investigate. If a fire is confirmed, the seccond stage or aduble evacuation alarm signal is initiated by a key switch in a manual pull station or a switch in the fire alarm control panel. If there is no fire, the first stage can be acknowledged, usually by a switch in the control unit. If the first stage or audble alert signal is not acknowledged within five minutes a timing circuit will automatically initiate the second stage or audible evacuation alarm signal

Question 7

What are the three principles that that automatic fire detectors operate on?

Answer 7

1. The detection of heat
2. The detection of visible and invisible products of combustion
3. The detection of infrared or ultraviolet radiation of flame

Question 8

What are the three basic types of heat detectors?

Answer 8

1. Fixed Temperature
   
   1. Fusible Link Detectors
   2. Bi-MetalDetectors
2. Rate of Rise detectors
3. Rate of anticipation detectors

Question 9

What are the two basic types of smoke detectors?

Answer 9

1. Ionization Detectors
   
   1. uses a very small radiation source mounted ina chamber that ionizes the nearby air. Two electrically-charged plates are positioned at each end of the chamber.
2. Photoelectric Detectors
   
   1. These operate on two principles: Light scattering and light obscuration
   2. These have an enclosed chamber that prevents the entrance of light from outside sources but allows for the entry of smoke
   3. Detector also contains an internal light source, a light barrier, and a photo-conductive cell

Question 10

What condition would be reported/indicated at a fire alarm panel as a result of the loss of water pressure preventing adequate water flow in an automatic sprinkler system?

Answer 10

Supervisory Condition

Question 11

When activating a manual pull station in a single stage fire alarm system, what condition would be reported/indicated at the fire alarm control panel?

Answer 11

Alarm condition

Question 12

Infrared flame detectors are particularly sensitive to…?

Answer 12

Glowing Embers

Question 13

According to page 113 of the Alberta Fire Alarm System Guide, a fire alarm system must be supplied by an emergency power supply that shall consist of…?

Answer 13

1. A Battery
2. A Generator
3. A Combination of the two

Question 14

What is the incipient stage of a fire?

Answer 14

• When there are no obvious signs of a fire and there is no sign of heat or smoke

Question 15

What are the two principles by which photoelectric smoke detectors operate?

Answer 15

1. Light Scattering
2. Light Obscuration

Question 16

A two-stage manual pull station consists of a single-pole switch activated by the pull mechanism to initiate an alert signal. The second switch is activated by the key switch to initiate an alarm signal

True or False?

Answer 16

True

Question 17

What condition would result in a fixed temperature/rate of rise detector giving a false alarm?

Answer 17

• A rapid increase in temperature or a rapid rate of rise, would cause a false alarm
• Such as a boiler room that has a rapid change in temperature

Question 18

What is the switching arrangement of a single stage manual pull station?

Answer 18

• One single pole switch

Question 19

What type of device would be most effective in areas where highly flammable liquids are handled or stored?

Answer 19

• A Flame Detector would be used
• Flame Detectors are used to protect areas where the anticipated flame from a fire is almost instantaneous, with little or no incipient or smoke stages
• Areas like fuel loading platforms, industrial process areas, and other hazardous areas where rapid fires can occur

Question 20

What are the two basic types of smoke detectors?

Answer 20

1. Ionization
2. Photoelectric

Question 21

Are smoke alarms part of a fire alarm system?

Answer 21

No, they are not

Question 22

What do photoelectric smoke detectors best respond to?

Answer 22

Large Smoke Particles

Question 23

What type of detector has the lowest false alarm rate but is the slowest to respond?

Answer 23

Heat Detector

Question 24

What type of detector is best suited to detect the earliest stages of a fire?

Answer 24

Smoke Detector

Question 25

Which type of detector is a line-of-sight device?

Answer 25

Flame Detector

Question 26

What are the two types of fire system signalling appliances?

Answer 26

1. Audible Signalling Appliances
2. Visual Signalling Appliances

Question 27

What is the maximum dBA sound pressure level in a normally occupied area? And why is there a maximum?

Answer 27

• 110 dBA
• To protect the hearing of people in close proximity to the alarm

Question 28

Where shall a visual signalling appliance be installed?

Answer 28

• Close to each required audible signalling appliance

Question 29

What is Fire Alarm System Ancillary Equipment?

Answer 29

• Ancillary equipment is safety equipment controlled by the fire alarm system but is not part of the fire alarm system
• Examples
  
  • Fire Department Signal Connection - when the system goes into trouble or alarm condition, an automatic signal is relayed to a central monitoring company which then notifies the fire department
  • Fire Department Disconnect Control - the fire alarm control panel may be equipped with a switch that will disconnect the system from the fire department signal connection so that the system can be repaired or tested without initiating an alarm
  • HVAC Control - can use auxillary contacts to involve various functions during an alarm condition
    
    • Supply fans can be shutdown to prevent fuelling the fire with input air
    • Dampers controlling air flow can be closed to prevent the movement of smoke to other areas
    • Exhaust fans can be turned on to remove smoke in the area where the fire exists
    • Stairwell pressurization can be maintained to prevent smoke from accumulating in the stairwells so that occupants can safely evacuate
    • Door release or door unlock - during an alarm, door releases or door hold-open devices allow fire doors to close and limit fire and smoke movement to other floors or areas. Door unlocks allow building occupants to evacuate the building through exits that are normally locked by an electrical locking mechanism
    • Elevator Homing - overrides the elevator control and automatically returns the elevator to the ground floor. These can be manually released by the firefighters during a fire. If the fire is located on the ground floor, the homing control will send the elevators to another floor
    • Agent Release - an exstinguishing agent is a substance such as dry chemical, carbon dioxide, foam, or gaseous compound that stops the spread of a fire by chemical or physical action. This can be released through a single head for local application or through several heads to flood an area
    • Automatic Sprinkler Systems -

Question 30

Do Smoke Alarms have to be permanently connected into an electrical circuit?

Answer 30

Yes

Question 31

What is the operating temperature of a heat detector above ambient temperature?

Answer 31

20-25 degrees Celcius

Question 32

Where would an Ultraviolet Flame Detector most likely be used?

Answer 32

A storage shed/area where gasoline is stored in containers

Question 33

A rapid increase in temperature will initiate an alarm condition at 1-3 degrees ahead of the preset temperature of a rate of anticipating temperature detector

True or False?

Answer 33

True