# Our sulphur hexafluoride (SF6) cylinder stock and equipment changed during the year. How does the Intergovernmental Panel on Climate Change (IPCC) mass balance net that out?

Canonical: https://senseible.earth/answers/sf6-cylinder-stock-and-new-equipment-mass-balance

Take the fall in cylinder stock, add gas acquired, subtract gas sent out, then subtract the net rise in nameplate charge of equipment. What is left is the loss. The IPCC calls this the utility-level mass balance (Equation 8.10) and says it suits where equipment has been in use for 10 to 20 years or more.

## Equation 8.10 in plain words

1. Decrease in SF6 inventory: gas in your cylinders at the start of the year minus gas in them at the end.
2. Add acquisitions: SF6 bought in bulk, plus SF6 bought inside or with equipment, plus SF6 returned to site after off-site recycling.
3. Subtract disbursements: SF6 inside equipment you sold to others, plus gas returned to suppliers, sent off-site for recycling or destroyed.
4. Subtract the net increase in nameplate capacity: nameplate charge of new equipment minus nameplate charge of retiring equipment.
5. The result is the user's emissions for the year, covering installation, use and disposal together.

## When the Guidelines say it fits

The Guidelines write the good-practice criteria for countries: installation, use and disposal losses are 3 percent or more of facility-level gas flows, equipment has been in use for 10 to 20 years or more, and sealed-pressure emissions are negligible. The equation itself is headed "Utility-level mass-balance approach" and is stated in facility-level gas flows, but applying the country criteria to one factory is our reading. If most of your panels are sealed pressure, this balance will miss their slow loss; add a factor for them as in our sealed-panel page.

The Guidelines also say the pure mass balance is not the right tool for processes losing about 3 percent of nameplate a year or less, because that is near the precision of the weighing.

## Why a new unit must not look like a loss

New equipment that arrives pre-filled is gas you acquired, and it also raises your installed nameplate charge. The two terms cancel in the equation, so a new breaker is not counted as an emission. Retiring a unit works the other way: its nameplate charge leaves the installed total, so any of its gas not recovered shows up as loss.

## One year at a plant with topped-up breakers

- Cylinders: 6 kilograms at the start, 3 at the end, so the decrease is 6 minus 3 = 3 kilograms
- Acquisitions: 4 kilograms bought in bulk
- Disbursements: 2 kilograms returned to the supplier
- No new or retired equipment: net rise in nameplate charge = 0
- Emissions = 3 + 4 minus 2 minus 0 = 5 kilograms of SF6
- Add a new 10 kilogram breaker delivered pre-filled: acquisitions rise by 10 and nameplate rises by 10, so 3 + (4 + 10) minus 2 minus 10 = 5 kilograms again

All quantities are examples. Weigh cylinders on the same scale at the start and end of the year and keep the weighing sheets.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into dated records. It does not read cylinder weights or switchgear nameplates, so keep the SF6 sheet yourself and add the kilograms to your inventory.

- [Switchgear gas never topped up: report zero?](https://senseible.earth/answers/sf6-switchgear-never-topped-up-report-zero)
- [Scrapping switchgear gas: share emitted](https://senseible.earth/answers/scrapping-sf6-switchgear-share-of-gas-emitted)
- [SF6 switchgear leaks in Scope 1](https://senseible.earth/answers/sf6-switchgear-leak-scope-1)

Sources: [IPCC 2006 Guidelines, Volume 3 Chapter 8 (Equation 8.10 and Section 8.2.2.1)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_8_Ch8_Other_Product.pdf)

Last reviewed 2026-11-05. Equation 8.10 is a utility-level balance in facility-level gas flows; only the good-practice criteria are written for countries, so applying them to a single site is our reading.