The information provided below is for guidance purposes only. Regulations 7, 8, 9 and 10, and Tables 1 and 2 of Schedule 1 of the Dangerous Goods Safety (Major Hazard Facilities) Regulations 2007 describe the requirements for determining whether the critical quantity of Schedule 1 substances is or will be exceeded.
1. Determine the quantity of Schedule 1 substances
Under Regulation 8, the quantity of a Schedule 1 substance at the site is determined by adding the following:
- the maximum quantity of the substance that could be present in:
- process vessels, interconnecting pipes and conveying systems
- storage tanks or vessels, or storage areas
- pipelines outside process areas
- the maximum quantity of the substance that could escape onto the site from an off-site pipeline connected to the site
- any other quantities not referred to above that are likely to be at the site.
If the substance is part of a mixture then the quantity is calculated using the formula:
a x b = c
a is the quantity of the mixture
b is the percentage of the substance in the mixture
c is the quantity of the substance of the mixture.
2. Determine the "threshold quantity"
Regulation 10 explains that the threshold quantity of a substance is determined by referring to Schedule 1. Threshold quantities are located in Table 1 for specific dangerous goods and Table 2 for specific category of substances.
For substances named in column 1 of Table 1, the threshold quantity is specified in column 3.
For substances not named in Table 1, where the substance belongs to a category in column 1 of Table 2, the threshold quantity is specified in column 2 of Table 2.
For substances belonging to more than one category in Table 2, the lowest threshold quantity applies.
3. Calculate the “critical quantity”
Under Regulation 9, the critical quantity of a Schedule 1 substance that is, or is likely to be, present at the place, depends on the number of Schedule 1 substances present and their threshold quantities.
Single Schedule 1 substance
Where only one Schedule 1 substance is present, or is likely to be present, the critical quantity is exceeded if there is more than 10 per cent of the threshold quantity for the substance.
Two or more Schedule 1 substances
Where more than one Schedule 1 substance is present, or is likely to be present, the critical quantity is exceeded if applying the following formula to the substances produces a result greater than 0.1 (i.e. 10 per cent, which is the threshold above which notification is required).
x, y... and n are the different Schedule 1 substances
qx ,qy... and qn are the quantities of x, y … and n
Qx, Qy, ...and Qn are the threshold quantities for x, y, … and n.
Only include the Schedule 1 substance if more than 2% of the threshold quantity is present.
Is the critical quantity exceeded?
Yes, inventory > critical quantity
All dangerous goods sites that intend to have quantities of dangerous goods greater than the "critical quantity" on site must notify the Chief Officer.
For more information look up Notifying that critical quantity of Schedule 1 substances will be exceeded.
The Chief Officer does not need to be notified. However, the Dangerous Goods Safety (Storage and Handling of Non-explosives) Regulations 2007 still apply.