| Thanks for the reply John. We are in the process of decontaminating the sub
| station just now. We did not know about the possibility of toxins until made
| aware of this by the equipment manufacturer, so we have been in and out of
| the sub, many times before starting clean up. However, very little has been
| touched.
Arced SF6 can produce disulfur decafluoride (S2F10), which is extremely toxic
on the scale of phosgene. It had even been considered as a possible chemical
warfare agent because, unlike phosgene, it produces no irritation and a lethal
level can be absorbed before the victim becomes aware of it. Freezing point
is -53C and boiling point is 30.1C. So it could be present in liquid form in
the substation, if it was not all gassified by the arc that caused the failure.
http://en.wikipedia.org/wiki/Disulfur_decafluoride
http://en.wikipedia.org/wiki/Sulfur_hexafluoride
http://en.wikipedia.org/wiki/Phosgene
| I don't thing this is an installation problem, as the circuit breaker has
| been in operation for a few years. We are focusing on the following as
| possible causes:
| 1.. Synchronising problem
| 2.. Excessive number of operations, 2439 ops.
| 3.. Loss of SF6 gas.
| The extent of destruction of the CB has taken everyone by surprise,
| including manufacturers and insurance investigators, so one of the questions
| is why did the switchgear fail so destructively. The CB was used well within
| its rating.
Maybe the excessive operations had accumulated enough S2F10 products that
would produce explosive gasification pressures under another fault.
Another possibility is a structural failure of the gas containment due to
other problems like cracking from extremely cold temperatures or from
temperature differences. Previous operations in cold temperatures could
have created extreme thermal differences, producing cracks in the container
or seals that will eventually either fail unless pressures that should
otherwise not fail, or allowed the gas to escape or be contaminated.
Did only one phase fail? If so, the other phase breakers should be inspected.
I'm sure the manufacturer would be suggesting this.
| If anyone had been in the sub station at time, it may well have been a
| fatality. If I get time later today, I will post some photos. onto an image
| hosting website.
I would be curious to see just how much explosive pressure was involved.
Can you report the normal current and possible fault current at the time
of failure?
