The "Gas Engineering Project Standard" GB 55009-2021 mandates the following:

3.0.7 Gas must have a warning odor that can be perceived by a person with normal olfaction when it leaks into the air before any danger occurs.

3.0.8 When the supplied gas does not meet the requirements of Section 3.0.7 of this standard, odorization should be carried out. The minimum amount of odorant should comply with the following provisions:

When a non-toxic gas leaks into the air and reaches 20% of the lower explosive limit, it should be detectable.

The "Urban Gas Design Standard"GB50028-2006 (2020 edition) also has similar requirements.

3.2.3 Urban gas must have a detectable odor, and the minimum amount of odorant in the gas should comply with the following provisions:

When a non-toxic gas leaks into the air and reaches 20% of the lower explosive limit, it should be detectable.

For different odorants, there are corresponding concentration values (K values) that can be perceived by people with normal olfaction, as specified in the "Urban Gas Odorization Technical Regulations" CJJ/T148-2010.

The formula for calculating the odorant concentration in gas is as follows:

Cn - Minimum odorant concentration at the endpoint (mg/m3).

K - Minimum concentration value (mg/m3) at which the odorant reaches the warning odor threshold in the air

L1 - Lower explosive limit of the gas in the air (volume fraction)

For natural gas (a mixture with a methane lower explosive limit of 5%), if we use the 5% lower explosive limit (L1) as per the formula above, the calculated Cn values for THT, TBM, and S-Free would be 8, 3, and 7 mg/m³, respectively.

This means that if tetrahydrothiophene (THT) is used as the odorant, the calculated minimum odorant concentration at the endpoint is 8 (mg/m³) when considering 0.08/(0.2×5%).

The standard calculation requires the minimum value at the user's endpoint. However, since the odorization point is usually within the station, this value is also influenced by factors such as season, odorization point, pipeline length, material, corrosion, gas composition, pressure, etc. Therefore, when setting up odorization in the station, the actual odorant dosage should be 2-3 times the calculated theoretical value.

The goal is to control the minimum odorant concentration at the endpoint to meet the Cn requirements.

Note:

1. The values in the table are recommended values. In actual engineering, the amount of odorant should be verified based on the K values provided by the supplier.

2. When the gas composition differs from the proportions in this table, the required amount of odorant for the gas can be calculated based on the lower explosive limit of the gas in air compared to natural gas with a 5% lower explosive limit.