ENGR403 FIRE ENGINEERING EXAM ANTHONY
ABU NOTES QUESTIONS ANSWERED
CORRECTLY
◉Radiation types . Answer: - Ultraviolet (specific bands)
- Visible (not super useful)
- Infrared (specific bands)
◉Ultraviolet . Answer: Formation of free radicals
- Electrons go to a higher energy state when hot, then when they cool
this energy is released as UV light
◉Infrared . Answer: Molecular movement
◉Visible light . Answer: Yellow flame
- Soot particles - particles get heated and glow
◉Premixed flame . Answer: Fuel and air mix before combustion
- check for UV as less soot produced
,◉Diffusion flame . Answer: Air mixes with fuel outside
- Real life fire
◉Gasses detection . Answer: - Want to detect something only fire
produces
--- CO and Soot
- PVC -> HCI
- Wool -> HCN
◉Aerosols (Soot) . Answer: Flaming fires
- Solid particles - soot
- 0.1 - 1 um
- Stick together and can be seen above fire
Smouldering fire - ciggys
- Liquid drops - tar and oil
- 1 - 10 um
Particles coagulate over time
◉Temperature - detection . Answer: Flaming fires - lots of heat
Smouldering fires - less heat
- Install CO sensors at waist height as smouldering fire smoke does not
rise up very hight
,Smoke can only rise if there is more than a 10 C difference in temp
between smoke and air
◉Sound - detection . Answer: Compression and rarefaction in air
thermal expansion of fuel upon heating
- non homogenoues fuels expand unevenly
◉Types of fire detectors . Answer: - Flame detectors - radiation
- Gas detectors - gasses
- Smoke detectors - aerosols
- Thermal detectors - heat
- Aspirating detectors - aerosols
◉Types of smoke detectors . Answer: - Ionisation chamber smoke
detector
- Photo electric smoke detector
- Linear beam detector
◉Ionisation chamber smoke detector . Answer: - issues with storage
- Ions attach to smoke particles passing through causing current to
decrease
◉Photo electric detector . Answer: Good for brighter smoke
, - e.g. wood has brighter smoke compared to kerosene (black smoke) less
diffraction, more absorption of light
Effect of size of particles, smaller particles scatter the light
- Receiver around 125 degrees
◉Effect of size of aerosol particles . Answer: Flaming fires
- Smaller particles - ionisation
- False alarm - smaller particles from cooking
Smouldering fire
- Big (tar droplet) particles - photoelectric
◉Linear beam detector . Answer: - Requires big particles
- Usually IR used
- Slower but good for factory or large warehouse
- Know the intensity from the emitter
- If intensity reduced by 20-30% therefore smoke present
◉Coefficient of extinction (Cs) . Answer: Io = inital light density at
emitter
I = light intensity at receiver
L = Distance (m)
Cs = extinction coeficcient (1/m)
ABU NOTES QUESTIONS ANSWERED
CORRECTLY
◉Radiation types . Answer: - Ultraviolet (specific bands)
- Visible (not super useful)
- Infrared (specific bands)
◉Ultraviolet . Answer: Formation of free radicals
- Electrons go to a higher energy state when hot, then when they cool
this energy is released as UV light
◉Infrared . Answer: Molecular movement
◉Visible light . Answer: Yellow flame
- Soot particles - particles get heated and glow
◉Premixed flame . Answer: Fuel and air mix before combustion
- check for UV as less soot produced
,◉Diffusion flame . Answer: Air mixes with fuel outside
- Real life fire
◉Gasses detection . Answer: - Want to detect something only fire
produces
--- CO and Soot
- PVC -> HCI
- Wool -> HCN
◉Aerosols (Soot) . Answer: Flaming fires
- Solid particles - soot
- 0.1 - 1 um
- Stick together and can be seen above fire
Smouldering fire - ciggys
- Liquid drops - tar and oil
- 1 - 10 um
Particles coagulate over time
◉Temperature - detection . Answer: Flaming fires - lots of heat
Smouldering fires - less heat
- Install CO sensors at waist height as smouldering fire smoke does not
rise up very hight
,Smoke can only rise if there is more than a 10 C difference in temp
between smoke and air
◉Sound - detection . Answer: Compression and rarefaction in air
thermal expansion of fuel upon heating
- non homogenoues fuels expand unevenly
◉Types of fire detectors . Answer: - Flame detectors - radiation
- Gas detectors - gasses
- Smoke detectors - aerosols
- Thermal detectors - heat
- Aspirating detectors - aerosols
◉Types of smoke detectors . Answer: - Ionisation chamber smoke
detector
- Photo electric smoke detector
- Linear beam detector
◉Ionisation chamber smoke detector . Answer: - issues with storage
- Ions attach to smoke particles passing through causing current to
decrease
◉Photo electric detector . Answer: Good for brighter smoke
, - e.g. wood has brighter smoke compared to kerosene (black smoke) less
diffraction, more absorption of light
Effect of size of particles, smaller particles scatter the light
- Receiver around 125 degrees
◉Effect of size of aerosol particles . Answer: Flaming fires
- Smaller particles - ionisation
- False alarm - smaller particles from cooking
Smouldering fire
- Big (tar droplet) particles - photoelectric
◉Linear beam detector . Answer: - Requires big particles
- Usually IR used
- Slower but good for factory or large warehouse
- Know the intensity from the emitter
- If intensity reduced by 20-30% therefore smoke present
◉Coefficient of extinction (Cs) . Answer: Io = inital light density at
emitter
I = light intensity at receiver
L = Distance (m)
Cs = extinction coeficcient (1/m)
