IEC 60480 GUIDELINES FOR THE CHECKING AND TREATMENT OF SULFUR HEXAFLUORIDE (SF6)
IEC 60480 GUIDELINES FOR THE CHECKING AND TREATMENT OF SULFUR HEXAFLUORIDE (SF6) TAKEN FROM ELECTRICAL EQUIPMENT AND SPECIFICATION FOR ITS RE-USE
10 Handling, storage and transportation
10.1 Introductory remark
Clause 10 deals with operations involving SF6 that has been in an electrical equipment enclosure and that may have been partially decomposed or contaminated. Such operations include removing and replacing the SF6 during maintenance or extension.

The need to handle used SF6 arises when
a) the gas pressure is topped up in closed pressure systems,
b) the gas has to be removed from an enclosure to allow for maintenance, repair or extension,
c) the gas has to be removed at the end of the life of an item of equipment,
d) samples of the gas need to be obtained, or the gas pressure measured, through temporary connection of a measuring device.

Safety provisions in this clause are applicable to all these situations; the two first situations arise mainly with respect to high-voltage equipment and may occur with medium-voltage GIS equipment, in particular if it is required to extend an existing switchboard. They do not arise with equipment using sealed pressure systems.

10.2 Gas handling equipment
When used SF6 has to be removed from an enclosure, caution shall be taken to prevent any avoidable release of the gas into the atmosphere and in particular into the work area.

Gas recovery equipment shall be used wherever possible to allow the gas to be stored, usually under pressure. Such equipment should be capable of evacuating the enclosure to remove as much of the gas as possible.

Gas recovery equipment is available which is specially designed for use with SF6 and is provided with reclaiming facilities for removing gaseous and solid decomposition products. This type of equipment is preferred, particularly for the removal of more heavily contaminated SF6, for example from circuit-breaker enclosures.

10.3 General safety requirements
Guidance for working safely with SF6 is required in order to anticipate the following hazards:
a) oxygen depletion (see 7.2.1);
b) freezing (see 7.2.3);
c) exposure to decomposition products (see 7.3).

Workers engaged in handling used SF6 shall be provided with personal safety equipment (gloves, safety glasses, etc.). The manufacturer's instructions and user's codes of practice shall specify which items of equipment are required for each situation listed in 10.1 (see IEC 61634).

Workers handling used SF 6 shall be familiar with the properties of SF6 decomposition products (Clause 5) and shall be aware of the risks to health (e.g. contact, inhalation, etc.) and the cautions necessary to minimize them. General safety recommendations are given in Clause 7 (see also IEC 61634).

10.3.1 Training of workers
Specific safety training shall be given to workers required to handle used SF6. It is not considered necessary that such workers have any pre-qualifying training or qualifications.

Workers shall be trained in the use of SF6 handling equipment used to transfer gas from an enclosure into a storage vessel. The manufacturer's operating instructions for such equipment should be complied with whenever it is used.

First-aid instructions shall be included in the safety training.

10.3.2 Facilities and services
Where enclosures containing used SF6 have to be emptied and opened, adequate washing facilities for workers should be available.

10.3.3 Outdoor working
When working outdoors, while removing used SF6 from an enclosure, no special precautions are necessary other than to prevent personnel from being exposed directly to its decomposition products, and to avoid release of SF6.

10.3.4 Indoor working
Indoor installations should be provided with adequate ventilation.

When used SF6 has to be removed from an enclosure in an indoor installation, it is necessary to ensure that the concentrations of potentially toxic decomposition products (e.g. HF, SO2, SOF2, SO2F2) remain at safe levels in the working area.

Ideally, this is achieved by direct measurement of the concentrations of the main contributor to toxicity, thionyl fluoride SOF2, and of the products of SOF2 hydrolysis, sulfur dioxide SO2 and hydrogen fluoride HF. For a medium level of decomposition, safe levels of these compounds are indicated by a maximum concentration of 200 µl/l of SF6 in the area (see IEC 61634). Nevertheless, this should not preclude the more important concern: avoiding the release of SF6.

A notice stating that open fires, smoking, heating to more than 200°C and welding without special precautions are prohibited and giving first-aid instructions (see IEC 61634) should be displayed while SF6 is being handled in an indoor location.

10.4 Condition of the SF6 in an enclosure
The condition of the used SF6 in an enclosure will depend on the types and energies of electrical discharges or arc that have occurred within it. Three situations are commonly found as follows:
a) SF6 is in an enclosure which does not contain active parts of a circuit-breaker and that is not linked to a circuit-breaker enclosure so that an exchange of gas cannot occur.
Gas: zero to low decomposition.
Solids: little or no powder deposits.

b) SF 6 is in an enclosure containing active parts of a circuit-breaker, or linked to such a compartment.
Gas: medium decomposition (by-product contents depend on the efficiency of the absorbent material used in this type of enclosure).
Solids: quantity of deposits will depend upon the current interruption history.

c) SF 6 is in any enclosure in which abnormal arcing occurred but where the enclosure did not open to the atmosphere through pressure relief valve or burn-through. In this case, an internal fault has occurred but a circuit-breaker has cleared the fault before the pressure in the enclosure has risen sufficiently to cause a release of SF6 .
Gas: high decomposition should be expected.
Solids: a large quantity of deposits is expected. Their compositions depend on which materials have been heated by the arc.

Information on sampling and testing SF6 taken from an enclosure is given in Annex A.

10.5 Removing used SF6 from an enclosure
Gas recovery equipment, as described in Annex C, shall be provided to allow SF6 to be removed whilst minimizing leakage to the atmosphere, and will preferentially contain means for reclaiming used SF6. Such equipment would normally comprise at least a vacuum pump, filter cartridge, compressor, suitable means for controlling the flow of the gas and a reservoir.

Gas that is not reclaimed on-site within the recovery equipment shall be sent to the gas manufacturer, reclaiming company or disposal operator (see Figure 1).

10.6 Storage and transportation of used SF6
Storage and transportation of new, un-used and used SF6 shall always be carried out fully in accordance with the local regulations.

Unavoidably, SF6 is temporarily stored in vessels, preferably cylinders, during reclaiming procedures and transportation to other locations for re-use in other equipment.

These cylinders should be specially colour-coded to avoid confusion between used and new SF6 (see Clause C.3).

The use of cylinders that were shipped with new SF6, or are labelled to have new SF6 in them, should not be used for storage of used SF6 at any time.

Most gas recovery equipment can use the same type of gas cylinders for storage as those supplied with new gas, provided they can pressurize the SF6 to 5 MPa. With this method, used SF6 gas can be stored at a safe ratio of 1 kg SF6 per litre volume without requiring special handling of the reservoir.