DGUV Information 213-013e - SF6-Switchgear and Equipment

3.3.1
Prior to usage, "new" pure SF₆ is odourless, tasteless, colourless and non-toxic. It does not contain any contaminants that might be hazardous to health.

For further requirements regarding the purity of SF₆, refer also to section 6.2.1. of DIN EN 60376 / VDE 0373-1.

3.3.2
The occupational exposure limit value (OEL) of SF₆ is 1,000 ml/m³ (ppm) or 6,100 mg/m³ as time-weighted average. In addition, there is a short-time value with an exceedance factor of 8 (TRGS 900 "Arbeitsplatzgrenzwerte"; Occupational exposure limit values OEL, English publication not available).

The "occupational exposure limit value" is the limiting value for a time-weighted average concentration of a chemical substance in the air with respect to a specified reference period at the workplace. OEL represents the concentration of a substance at which acute or chronic adverse effects on general health are not anticipated. This is a time-weighted average within an 8 hour period.

The exceedance factor prescribes the permissible maximum concentration peak levels for a hazardous substance. An exceedance factor of 8 means that the average ambient SF₆concentration at the workplace must not exceed 8,000 ppm or ml/m³or 48,800 mg/m³within a 15-minute period. Longer exceedance periods are also permissible as long as the product of the exceedance factor (EF) and the exceedance period is retained (e.g.: EF 4 over 30 minutes is comparable to EF 2 over 60 minutes).

The duration of the increased concentration may not exceed one hour in a single work shift (refer to TRGS 900 "Arbeitsplatzgrenzwerte", Sec. 2.3).

The rationale for determining the OEL for SF₆, can be found in H. Greim (ed.): "Gesundheitsschädliche Arbeitsstoffe; Toxikologisch-arbeitsmedizinische Begründung von MAK-Werten" ("Harmful substances and materials; toxicological and occupational medical reasons for MAK values"), WILEY-VCH, Weinheim, 1997, P. 1-32 in German.

3.3.3
SF₆ is approximately five times denser than ambient air and tends to sink and collect at lower levels. If allowed to escape into the work environment in large quantities, SF₆ will displace the oxygen required for breathing (risk of suffocation). SF₆ concentrations greater than 19 % vol. will reduce the percentage of oxygen in breathable air to less than 17 % vol., for which special protective measures are required according to Appendix 4.

A risk of suffocation exists in improperly opened, non-vented SF₆gas compartments, for example, or where relatively large quantities of SF₆leak from SF₆gas compartments or SF₆pressurized gas containers as a result of technical defects. The risk is enhanced where insufficient ventilation is available at the floor levels of small, enclosed equipment rooms, including the rooms located immediately below, such as basement facilities, cable ducts, maintenance shafts, pits, drainage systems, etc.

3.3.4
SF₆ switchgear and equipment in use can contain solid or gaseous decomposition products. SF₆ decomposition products may be toxic and harmful to health when inhaled, ingested or exposed to skin. Furthermore, they may irritate the eyes, respiratory system or skin and possibly cause chemical burns.

Inhalation of large quantities of decomposition products can increase the risk of lung damage (toxic pulmonary oedema). Nevertheless, even small amounts of gaseous decomposition products will produce certain symptoms within seconds that can serve as a warning - before a risk of poisoning ensues - allowing workers to promptly evacuate to a safe location. These symptoms might include unpleasant or acrid odours as well as irritation of the nose, throat and eyes.

In particular, hazards associated with decomposition products can exist when a gas leakage occurs due to a fault, when opening or working with exposed SF₆circuit breaker switching chambers, or when a fault arc occurs in an SF₆gas compartment (refer also to Appendix 4).

Regarding the OEL for SF₆decomposition products (Sec. 3.2.2), refer to TRGS 900 "Arbeitsplatzgrenzwerte" and DIN EN 622714/VDE 06714:201406 Annex H.1.

3.3.5
Rapidly escaping SF₆ from a gas container can cause ice formation, which creates the risk of frostbite if it comes into contact with persons who are insufficiently protected.