Three people in critical condition from Google data center 'electrical incident'

All of it freezes on contact with solid surfaces, often the eyes and exposed body parts of the victims.

Here's a good (SFW) video demonstrating an arc flash: https://youtu.be/bPifdBpcMRY

It's basically a small explosion.

The hot metal then ignites in air adding even more heat to the explosion.

> The pressure wave created by an arc flash explosion has the force of thousands of pounds per square inch. This is powerful enough to knock down or throw nearby workers and at the same time cause damage to the eardrums, lungs, brain and other vital organs.

https://www.electricityforum.com/iep/arc-flash/electrical-ar...

(I didn't know that, and just found that explanation while looking for an answer to your question.)

A different risk is that electric current passing through the body could cause muscle convulsions, which could also cause someone to move or fall suddenly or erratically.

There are systems (permits to work, lock out tag out, risk assessments, etc.) in place to maintain worker safety mandated by law. An incident of this kind typically means that there was a failure with one of more levels of the system... Someone did something they weren't supposed to, they turned off the wrong equipment, they didn't turn off the equipment before working on it, etc.

> And trying to extinguish such an arc can be quite a challenge.

Once established, an arc can continue as long as current is still flowing. It's possible for arcs to continue and still be below the trip current of the upstream circuit protection. In non-catastrophic scenarios, you have mechanisms to "quench" an arc... one method is to use compressed air.. like blowing out a very hot, angry candle on a birthday cake.

Of course you need to keep in mind that courts in Europe tend to not hold to the letter of the law quite as strongly as US courts seem to do. Laws like these are mostly so the judicial system gets booted up when something awful happens. Might still turn out that no one was responsible for the accident. Might turn out the boss of the guy throwing the switch was responsible. Or the equipment manufacturer.

I'm not familiar with the details of this accident, but in general, not necessarily. Air is normally an excellent insulator. But when voltages are high enough, the molecules ionize, become conductive and transmit current. This is a path-dependent process, meaning that once it begins, the voltage can drop below what is required to begin the process while maintaining current.

So an arc caused by a system with low capacitance (or total count of free electrons on the negative side) may quickly transfer all the free electrons, lowering the voltage enough to close the circuit. But anything connected to mains power will have an essentially infinite source of more electrons, meaning there won't be a voltage drop big enough to close the circuit. I'm being a little handwavy with the physics concepts, but hopefully the point is clear.

This can be thought of as a sort of hysteresis: the dependence of the state of a system on its history.

Edit: If you want to go down a rabbit hole, check out the solutions used in power substations as circuit breakers. It's not enough just to mechanically separate the connection, so they use systems like these:

https://en.wikipedia.org/wiki/Sulfur_hexafluoride_circuit_br...

https://www.codrey.com/electrical/air-blast-circuit-breaker/

It does not burn easily but once aluminum has ignited it can continue to burn under normal atmospheric conditions, especially if it begins to melt and boil.

It burned until there was no more silver color metal left, leaving just the copper wire leads. I assume it was aluminum, I think steel would be harder to burn.

I do remember unplugging it during the fire, but it didn't take very long to burn, so I might have done it after it was over.