HAS 871 Assessment 3 - ALOHA worksheet
There are two parts to this worksheet.
You need to complete both parts:
Part 1 – Pool fire and thermal radiation calculations
Part 2 – Toxic gas release and toxicity calculations
When you have entered information into ALOHA record it in the right hand
column and answer any questions asked.
Part 1 - Pool Fire – n-octane
Step 1 – Insert Site Data
Set up your session for Metric
units
 Go to menu tab “ Display”
 Go to “Display Options”
 Select “Metric”
You need to do this every time
you use ALOHA
List your location – Select
Wollongong
Location: Wollongong, NSW, AU
Building: single storied with unsheltered surroundings
Select Date and Time –
this may be important if you are
choosing a stability class and
windspeed that can only occur
at certain times eg night.
You may need to select more
than one time.
Date and Time:12th April 2022 22:30 (Stability D)
Date and Time: 12th April 2022 12:00 (stability A)
Step 2 - Setup
Select Chemical
Select n-octane
Chemical: n-octane
N-octane is a chemical that has
similar properties to petrol.
Select Atmospheric Data
Windspeed – 4 m/s
Wind Direction North
Measurement height above
ground 3m
(stability D)
Windspeed 4m/s
Wind Direction N
Measurement height above ground 3m
(stability A)
Windspeed 1m/s
Wind Direction N
Measurement height above ground 3m
Select Ground Roughness
This impacts on the amount of
mixing that the gas will do due
to boundary effects and water
can affect vapourisation rates
due to temperature
Select Open country
Select Cloud Cover
This changes the amount of
incoming solar radiation which
can impact of evaporation rates
and mixing of atmospheres
Cloud Cover: partly cloudy
Select Air Temperature
Enter 25 degree Celcius
Stability Class
Initially select D with wind
speed of 4 m/s.
You will need to vary this to
complete the table below
Inversion Height
Humidity
This impacts on the amount of
heat radiation absorbed in the
water in the air
Select Humidity : Medium(50%)
Part 3 - Source
Set Up
Using the “set up” tab from the
menu select Source -source type
Tank
Select vertical cylinder
Ground roughness: open country
Cloud Cover: partly cloudy
Air Temperature: 25 C
(step please see below graph)
Initial Selection: D
No inversion (step please see below graph)
Humidity: 50%
Tank Type: Vertical
Tank diameter: 20m
Height: 10m
Volume of tank: 3142m3
Enter tank diameter = 20m
Enter tank height = 10m
What is the volume of the tank
in cubic m?
Chemical State and
State of the chemical in the tank: Liquid
Temperature
Chemical stored at: 25 C
Enter the state of the chemical liquid
Enter the storage temperature –
25 deg Celsius
Volume in the tank – 90% full
Volume in tank : 90% full = 2827m3
Type of Tank Failure
Select:
Leaking tank, chemical is
burning and forms a pool fire
Circular opening 0.3 m diameter
Short pipe or valve
Height from bottom of tank
0.5m
What is the scenario?
Leaking tank, chemical is burning and forms a pool
fire.
Size of puddle in square meters
900 m2
Area and type of leak
Circular opening 0.3 m diameter
Short pipe or valve
Height from bottom of tank
0.3m
Size of puddle in square meters
900 m2
Opening diameter: 0.3 m
Leak is through: short pipe / valve
Height of the tank opening
Height above the bottom of the
tank 0.5m
Height above the bottom of the tank: 0.5m
Maximum puddle size
Enter Maximum area 900m2
Maximum puddle size: maximium area: 900m2
Part 4 – Results – part 1 effect of wind speed on Radiation levels
From the calculated results list
Maximum flame length: 37m
the following information:
Burn Duration: limited to 1 hour by ALOHA
Maximum flame length
Max Burn rate: 3090 kg/min
Burn Duration
Total amount burned: 183603kg
Max Burn rate
Puddle diameter: 28m
Total amount burned
Puddle diameter
Heat radiation levels
Select “Display” from menu
Red threat zone: 23 kW/m2
Select “Threat Zone”
Orange threat zone: 12.5 kW/m2
Enter your own level of concern Yellow threat zone: 4.7 kW/m2
(LOC)
23.0 kW/m2
12.5 kW/m2
4.7 kW/m2
Stability Class : A
Stability Class : D
Document Results
Record results
Wind Speed: 1 m/s
Wind Speed: 4m/s
Vary the wind speed and
here:
stability class to determine
23.0 kW/m2
39m
53m
2
effect of wind speed on
12.5 kW/m
57m
69m
2
radiation levels
4.7 kW/m
95m
104m
Cut and paste Threat Zone data from text and thermal radiation threat zone plot from
text summary here:
Stability class D, 4 m/s information
Stability class A, 1 m/s information (0.3)
Part 4 – Results – part 2 – Effect of distance on radiation levels
Using Stability class D, 4 m/s
Max Thermal Radiation
Downwind distance (m)
Radiation Levels at a
(kW/m2)
nominated distance
Select “Display” from menu
20
92.3
Select “Threat at Point”
40
38.6
Enter “downwind distance”: variable
60
17.4
Enter “cross wind distance”: 0 m
80
8.89
Record Maximum thermal radiation in
table below – use information from
100
5.18
the text summary page
120
3.35
Document Results
140
2.32
Vary the downwind distance to
160
1.69
determine effect of distance on
thermal radiation levels
180
1.29
200
1.01
Insert at least one Screen shot of Text Summary and graphic for “Threat at Point”
Graph your results in excel and display here
Graph the effect of how the radiation levels change with distance.
Max Thermal Radiation (kW/m2)
Max Thermal Radiation level (kW/m2) along downwind distance (m)
100
80
60
40
20
0
0
50
100
150
200
250
Downwind distance (m)
Table 1. Max thermal radiation level (kW/m2) along downwind distance(m)
The table shows the max thermal radiation level decreases with further downwind
distance.
Sensitivity Analysis.
A sensitivity analysis is when you consider the impact of changing a variable on another
variable.
1) Comment on the difference that the different stability classes and wind speed
make on the radiation levels at different distances. Why might this be the case?
The radiation tend to spread wider under a more stable atmosphere with higher wind
speed. The stability and wind speed can explain this phenomenon.
Under a less stable class (i.e. class A), the dispersing gas mixes to atmosphere rapidly
since there is more turbulent due to incoming solar radiation. With low wind speed, the
gas is not spreading wide as it tend to develop and mix vertically, vice versa.
Therefore the threat zone of class A low wind speed is short than class D high wind speed.
2) Comment on how the thermal radiation level (kW/M2) changes with distance.
Shorter the downwind distance, the higher the radiation level. The trend decreases
exponentially along with longer distance, the radiation level reduced to one-third per
20m further from downwind distance.
Application of thermal radiation levels to humans.
If you were fighting the fire, with normal work clothes, how close could you be. Explain
your reasoning.
Using class D with 4m/s case, if I were fighting fire with fire fighting PPE, I would be able
to withstand maximum 3kW/m2 (NSW Rural Fire Service, 2010), which indicates 126m is
my closest distance to pool of fire (as shown in Figure 2). However, with only normal
clothings, the limitation of heat flux can be received by a person is no more than 1.5
kW/m2 (Raj, 2008). By adjusting the thermal radiation threat zone, the closest distance is
168m from the pool of fire (as shown in Figure 1).
Figure 1 Threat zones under normal clothings
Figure 2 Threat zones under fire fighting PPE
Part 2 – Toxic gas release - chlorine
Step 1 – Insert Site Data
Set up your session for Metric units
 Go to menu tab “ Display”
 Go to “Display Options”
 Select “Metric”
You need to do this every time you
use ALOHA
List your location – Select
Wollongong
Location: Wollongong
Infiltration Building Parameters
Select Building Type – this impacts
on the amount of toxic chemical
that can enter the building
Select: single storied dwelling
Building Surroundings: Unsheltered
surroundings
Building Type: single storied building
Building Surroundings: unsheltered surroundings
Select Date and Time –
this may be important if you are
choosing a stability class and
Time: 13th April 2022 02:00 (night)
windspeed that can only occur at
certain times eg night.
Select time suitable for :
Stability Class F
Windspeed 1 m/s
What is the windspeed and atmospheric conditions
required for Stability Class F?
Class F is the most stable class.
Windspeed: low wind speed
Atmospheric condition: low temperature, clear
sky
Step 2 - Setup
Select Chemical
Select Atmospheric Data
Windspeed – 1 m/s
Wind Direction North
Measurement height above ground
3m
Select Ground Roughness
This impacts on the amount of
mixing that the gas will do due to
boundary effects and water can
Chlorine
Use these values for sensitivity analysis in step4.1
Windspeed – 1 m/s
Wind Direction North
Measurement height above ground 3m
(steps please see above)
Ground roughness: Open country
(steps please see above)
affect vapourisation rates due to
temperature
Select Open country
Select Cloud Cover
This changes the amount of
incoming solar radiation which can
impact of evaporation rates and
mixing of atmospheres
Cloud Cover: clear
Select Air Temperature
Enter 10 degree Celsius
Stability Class
Initially select F with wind speed of
1 m/s.
Cloud Cover: Clear
(Steps please see above)
Air Temperature: 10 C
Initial Selection: F
See table below
You will need to vary this to
complete the table below
Inversion Height
Humidity
This impacts on the amount of heat
radiation absorbed in the water in
the air
Select Humidity : Medium(50%)
Step 3 - Source
Set Up
Using the “set up” tab from the
menu select Source -source type
Tank
Tank Size and Orientation
Tank orientation – horizontal
cylinder
Tank Diameter 0.76 m
Tank Length – 2 m
No inversion (Please see steps above)
Humidity: 50% (Medium)
(Please see steps above)
Tank orientation – horizontal
Tank Diameter – 0.76m
Tank Length – 2m
Volume – 0.91 m3
Chemical State and Temperature
Enter the state of the chemical –
Tank contains liquid
Chemical stored at ambient
temperature
Chemical state in tank: liquid
Ambient temperature: 10 C (environmental temp)
Mass or pressure of gas:
Mass in tank: 1000 KG
Enter the mass in the tank: 1000kg – Liquid Volume is: 0.69m3
the program will calculate the liquid %full is: 76.4%
level
Area and Type of Leak
Opening type: Circular
Opening diameter 0.01 m
Leak: Short pipe or valve
Opening type: circular
Opening diameter: 0.01 m
Leak: short pipe/valve
Height of Tank Opening
0.01m above the bottom of the
tank.
% of the way to the top of the tank: 1.32%
Part 4 .1 – Results – Effect of distance on toxic concentration
Toxic Concentrations
Results at each LoC
Select “Display” from menu
Red LoC(m): 364 m
Select “Threat Zone”
Orange LoC (m): 1800 m
Enter the following level of concern Yellow LoC(m): >10000 m
(LOC)
Fatal dose – 150 ppm
IDLH – 10 ppm
Odour threshold- 0.1 ppm
Cut and paste Toxic Threat Zone graphic here
Shelter in place as an option.
Impact inside a “shelter in place”
location varying no of room changes
per hour.
Assume location 200m downwind.
No of room
changes per hour
Indoor
concentration
inside room 200m
away from source
(ppm)
Outdoor
Concentration,
200m from source
2.04
6.08
19.8
56.3
157
309
449
449
449
449
449
449
PPM from 200m downwind
0.01
0.03
0.1
0.3
1
3
Graph your results in excel and display here
500
400
300
200
100
0
0,03
0,1
0,3
1
3
No of room changes per hour
Indoor concentration inside room 200m away from source (ppm)
Outdoor Concentration, 200m from source
The maximum concentration with 3 rooms of change per hour.
Part 4 .2 – Results – Effect of wind speed and stability class on toxic concentration
Toxic Concentrations
Red LoC(ppm): 150 ppm
Select “Display” from menu
Orange LoC (ppm): 10 ppm
Select “Threat Zone”
Yellow LoC(ppm): 0.1 ppm
Enter the following level of concern
(LOC)
Fatal dose – 150 ppm
IDLH – 10 ppm
Odour threshold- 0.1 ppm
Day temperature 25 deg Celsius
Night temperature 10 deg Celsius
Select Date and Time
Choose 11:00am for a day time
Choose 11:00pm for night time.
Stability Class and Wind Speed.
Notation: Example F 1
F refers to the Stability Class
1 refers to the wind speed in (m/s)
Insert Screen shot of Text Summary
for the each “Threat Zone” for each
F1, A1 and B1 conditions
Day Time: 1100 25 C
Night Time: 2300 10 C
Stability class
and Wind
Speed
Distance to
150 ppm (m)
A1
B1
B2
B3
C3
D4
D5
D6
F1**
330
342
278
222
267
225
209
193
364
*assume max distance 10Km
** remember to change to night conditions –
temp and time
Distance to
10 ppm (m)
Distance to
0.1 ppm *(m)
1400
1600
1100
912
1100
996
895
815
1800
8800
9900
10000
9300
10000
10000
9900
9000
10000
distance to certain concentration (PPM)
A1 text summary
B1 text summary
F1 text summary
Graph the stability classes and distances to 150ppm and 10ppm in excel and display
here
2000
1800
1600
1400
1200
1000
800
600
400
200
0
A1
B1
B2
B3
C3
D4
D5
D6
F1
Stability classes and Wind Speeds
Distance to 150 ppm (m)
Distance to 10 ppm (m)
Reflect on what you have learnt about these two sensitivity analyses.
1) How changing the no of room changes per hour impacts on the indoor
concentration levels
The higher the changing rate, the difference between indoor and outdoor decreases, as
air change rate increased, more gas from outdoor will be ventilated to indoor,
eventually increase indoor concentration.
2) How the stability class and wind speed change the distances to different
concentration levels
The distance to 150 ppm is not affected much by stability classes and wind speed,
however, for 10 ppm, it shows the stronger the wind speed, the shorter the distance to
10ppm (comparing B1, B2, B3). While in an atmospheric stable environment, the
distance to reach 10 ppm is further with a calmer stability class (comparing A1, B1, F1).
Consider the implications for designing a location to shelter in place for Chlorine and
also the importance of understanding the weather conditions during an emergency
situation (max 250 words).
In ideal situation, chlorine should be stored in an indoor place, where gates and doors
can be sealed if leakage occurred in order to prevent the spread. For the location to
shelter in place, the closer to the place of incident, the lower the number of room
change of the shelter should be in order to avoid contaminant got indoor through
ventilating system, such as switching off air conditioning, and close all doors and
windows (Bennett, 2009). Door gaps or holes that may let gas get indoor should be
covered by wet towel in order to create a safe room (Bennett, 2009).
Under different weather conditions, the spread of leakage of chlorine will be affected.
The higher the wind speed, the longer the distance of contaminant will spread, as well
as a narrower wind direction confidence lines. Whilst with low stability, such as
daytime, with low wind speed, the distance of spread will be shorter however, the
potential affected area will be wider since mixing of air is active, the contaminant is not
tend to spread along downwind (Law and Gimbun, 2020). Since the potential affect area
is larger, more residents should be informed to take shelter in place to prevent injuries.
Moreover, under F1 stability class, which may be at midnight, extra time for informing
residents should be expected as people will be asleep.
BENNETT, J. S. 2009. A systems approach to the design of safe-rooms for shelter-in-place.
Building simulation, 2, 41-51.
LAW, W. P. & GIMBUN, J. 2020. Modeling the effect of hypothetical chlorine leakage from
Malay-Sino Chemical Industries using ALOHA software and development of an
emergency evacuation route around Teluk Kalong industrial area. IOP Conference
Series: Materials Science and Engineering, 736, 72015.
RAJ, P. K. 2008. A review of the criteria for people exposure to radiant heat flux from fires.
Journal of hazardous materials, 159, 61-71.
The National Diet of Japan. 2012. The official report of The Fukushima Nuclear Accident
Independent Investigation Commission. The National Diet of Japan. Japan, Viewed
20th Apr 2022, <https://www.nirs.org/wp-content/uploads/fukushima/
naiic_report.pdf>