SAFETY HEALTH & WELLBEING
GAS RISK CALCULATOR
1. INTRODUCTION
The gas risk calculator can be used as part of an initial risk assessment when assessing the risk of:
•
•
•
Toxic effects from carbon dioxide (CO2) release from compressed carbon dioxide or sublimation
of solid dry ice,
Asphyxiation due to the accidental release of compressed gases and cryogenic liquids which will
displace available oxygen,
Fire in an oxygen enrichment environment following the accidental release of compressed
oxygen.
The gas risk calculator should be used with reference to the Guideline for Working with Gases.
1.1 SPECIFICATIONS
This tool is best used with the latest versions of GoogleChrome and Mozilla Firefox for full functionality.
2. FEATURES
After all information has been entered click on Calculate Result to view the results table. Further
calculations can be added to the results table by entering different values and calculating the result, which
will allow a comparison of scenarios. When all calculations are complete select Save as PDF. A Unikey
will be needed to download the PDF. (Note report does not appear on the first download, simply go back
to the calculator page and click save as PDF again).
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SAFETY HEALTH & WELLBEING
2.1 EXAMPLE OF PDF REPORT
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3. CARBON DIOXIDE CYLINDER RELEASE
The carbon dioxide tab calculates the % carbon dioxide in the room after a complete and catastrophic
cylinder release of CO2 gas from a nominated number of compressed gas cylinders. This value is
compared to the Time Weighted Average (TWA) exposure standard to assess the risk of the gas release.
Enter:
•
•
•
Dimensions of the room in metres*
Size of the compressed CO2 gas cylinder ( D, E or G size cylinders),
Number of cylinders
*The room height is limited to 1.8 m (breathing zone) as carbon dioxide has greater density relative to air
(x 1.5) and will sink on release.
Risk rating carbon dioxide release:
%
> 0.5
%
≤
0.5
Low risk
to
3.0
Medium risk – exceeds TWA (0.5%)
>
3.0
High risk – exceeds TWA and STEL
(3.0%)
Assumptions:
1. Initial concentration of carbon dioxide is 0.04%
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SAFETY HEALTH & WELLBEING
2.
Temperature of expanded volume adjusted to 21°C using the Combined Gas Law from cylinder
volumes reported at standard temperature and pressure of 15°C and 101.3kPa.
3.
Expanded volume of released gas is never lost (i.e. there is no ventilation).
4. CRYOGENIC LIQUIDS, OTHER GASES AND OXYGEN (O 2 ) RELEASE
These tabs calculate the % oxygen in a room after the complete release of a nominated number of
compressed gas cylinders or dewars of cryogenic liquid.
Enter into the calculator:
Compressed Gas
Cryogenic Liquid
•
Dimensions of the room in metres,
•
Dimensions of the room in metres*
•
Size of the compressed gas cylinders ( D,
E or G size cylinders),
•
Cryogenic liquid ( nitrogen, argon, helium)
•
Number of cylinders
•
Dewar size ( L)
Gas ( nitrogen, argon, helium)
•
Cryogen ( nitrogen, helium, argon)
•
*The room height is limited to 1.8 m as cold cryogenic gas will initially sink to the floor
Risk rating for oxygen depletion (gas release with risk of asphyxiation, other than carbon dioxide):
%
%
19.5
19.4
Low risk
to
18
Medium risk
>
3.0
High risk
Risk rating for oxygen enrichment:
%
≤
23.5
Low risk
>
23.5
High risk
Assumptions:
1. Initial concentration of oxygen is 20.9%.
2. Temperature is 21°C and pressure is 101.3kPa.
3. Expanded volume of released gas is never lost and is evenly displaced in the air.
Please note that different manufacturers and differently pressurized cylinders can contain different
volumes of compressed gas. For example BOC industrial nitrogen G size cylinder (032G) will contain 7.2
3
m3 of gas, whilst the industrial nitrogen, extra high pressure (033EHP) contains 11 m of gas.
In these calculations the Supplier volumes, as shown in Table 1, have been used (as stated at 15 °C on
the cylinder).
Table 1: Gas volumes used in calculator
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SAFETY HEALTH & WELLBEING
Gas
3
3
3
G (m )
E (m )
D (m )
Nitrogen
7.2 (BOC 032G)
3.6 (BOC 032E)
1.4 (BOC 032D)
Helium
7.3 (BOC 820G)
3.6 (BOC 820E)
1.4 (BOC 820D)
Argon
8.6 ( BOC 061G)
4 (BOC 061E)
1.6 ( BOC 061D )
Oxygen
8.075 (BOC 400)
4 (BOC 400
1.6 (BOC 400
5. CUSTOM GAS
Custom gas calculations allow entry of specific expanded gas volumes. The expanded gas volumes can
3
generally be found on gas cylinder labels as in point 6. of Figure 1. The volume units are m of gas. In
o
the gas risk calculator, these expanded volumes at 15 C have been corrected using the ideal gas law to
o
give a modified gas volume value at 21 C.
Figure 1: A compressed has cylinder label
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SAFETY HEALTH & WELLBEING
6. DRY ICE CARBON DIOXIDE RELEASE
There are many variables which determine the rate at which dry ice sublimes. These may include:
•
•
•
The physical form of the dry ice; e.g: pellets and flakes sublime at a faster rate than blocks.
Ambient temperature; the rate of sublimation increases at higher temperature
The degree of insulation provided by the container.
There are three calculation models provided for dry ice:
1. All dry ice spontaneously releases
2. 14% of the total mass of dry ice sublimes per hour
3. 1% of the total mass of dry ice sublimes per hour
Enter:
•
•
•
•
Dry ice calculation model
Dimensions of the room in metres*
Quantity of dry ice in kg
For calculation model 2 and 3, the length of time sublimation is allowed to occur
*The room height is limited to 1.8 m (breathing zone) as carbon dioxide has greater density relative to air
(x 1.5).
Assumptions:
1. Initial concentration of carbon dioxide is 0.04%
3
2. 1kg of dry ice will produce 0.45 m of gas.
3. Expanded volume of released gas is never lost and is mixed homogenously.
7. REFERENCES
1. AS 4332:2004 The storage and handling of gases in cylinders
2. AS 2243.10:2004 Safety in laboratories – Storage of chemicals
3. AS 1894:1997 The storage and handling of cryogenic and refrigerated liquids
8. DOCUMENT CONTROL
Acknowledgements
Safe Use of Carbon Dioxide in Laboratories (Guidance Note GN 028), Imperial
College, London, 2004.
Related Documents
WHS_CHE_GUI_1_Guideline for Working with Gases
Version
Control
Author/s
Custodian
Approved by
Amendment
Sandra Chapman, WHS
Specialist (Chemical)
Manager, Work
Health & Safety
Services
Director, Safety
Health & Wellbeing
Original
1.0
Date
released
Printed copies of this document are uncontrolled. Verify version before using.
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