…for a week.
For those that don’t know, a big generator spins in hydrogen as there is less friction.
To do certain generator maintenance that hydrogen must be removed. This is done by pumping out the hydrogen and replacing it with nitrogen.
This is because nitrogen and hydrogen are a safe mix, and air and nitrogen mix are also safe.
However, air ( oxygen-rich) and hydrogen are not to be mixed within the generator casing.
If there is a spark there will be a loud popping noise.
In this case, it woke people living 20 km away.
The end caps of the generator were emancipated, and the power station roof for that unit was blown off.
This happened at night and thankfully no one was physically hurt, barring, of course, the nightshift staff that were treated for shock.
I pasted the interesting bits below, but it appears that they use CO2 instead of nitrogen for some reason. I guess any gas that, when combined with hydrogen, does not form an explosive mix should do the trick.
“The incident occurred during the activity to displace hydrogen with carbon dioxide and air respectively, for the purposes of finding an external leak,” said Eskom spokesperson Sikonathi Mantshantsha. “Following the power station preliminary investigation, it appears that while performing this activity air was introduced into the generator at a point where hydrogen was still present in the generator at sufficient quantities to create an explosive mixture, which ignited and resulted in the explosion.”
“It also appears that there was a deviation from the procedure for carrying out this activity.”
Eskom will place those employees who were responsible to manage and execute this work under precautionary suspension pending the conclusion of an investigation into the explosion.