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You are forbidden by law (and mandated to report) such arcs in Europe. In Germany people who work in such environments have to have a few special certificates a

by atoav 4y ago

You are forbidden by law (and mandated to report) such arcs in Europe. In Germany people who work in such environments have to have a few special certificates and PPE that looks like they are trying to defuse a bomb. Arc flashes like that can burn with 10000 to 15000 degrees celsius and if you are close by not only will they send you flying, you are probably dead before you hit the ground. And trying to extinguish such an arc can be quite a challenge.

vsnf 4y ago
> will they send you flying What is the mechanism by which an object would be propelled when hit by such an arc?
- ars 4y ago
  The heat of the arc rapidly expands air (like a lighting bolt), the heat of the arc also vaporizes the metal conductor, and the vaporized metal expands rapidly, and enormously. It's basically a small explosion. The hot metal then ignites in air adding even more heat to the explosion.
- mediaman 4y ago
  There is an explosive heating of air that’s like a bomb going off.
- schoen 4y ago
  Apparently mainly air pressure: > 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-arc-blast 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.
Semaphor 4y ago
> You are forbidden by law (and mandated to report) such arcs in Europe. You are forbidden by law to have an accident? This misunderstanding is probably because of my lack of knowledge, but what do you mean? > And trying to extinguish such an arc can be quite a challenge. I only read about them in this thread, so I’m probably missing something again, but isn’t it an instantaneous thing and not something you need to extinguish?
- c_o_n_v_e_x 4y ago
  >You are forbidden by law to have an accident? This misunderstanding is probably because of my lack of knowledge, but what do you mean? 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.
- Doxin 4y ago
  You are forbidden by law to have an accident of this nature. Yes. If you do cause an accident of this nature you are criminally negligent no matter the circumstances leading up to the accident because it's your duty to ensure it doesn't. 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.
  - chrisseaton 4y ago
    Doesn’t make having an accident illegal make it more likely that people won’t report the accidents and won’t learn and improve?
c_o_n_v_e_x 4y ago
Arcs are rated by calories per square centimeter. There's a lot factors that go into arc ratings, more than just voltage. To give a frame of reference, a flame from a lighter on the tip of your finger for 1 second is considered 1 calorie. Arc flash PPE ratings start at 4 calories and can go above 100. The high cal rated PPE does indeed look like bomb squad gear.
- MayeulC 4y ago
  It's weird to rate it in calories (∝ joules, W.s) instead of Watts.
  - closewith 4y ago
    Energy is used rather than power as it's the cumulative effect in energy incidents that causes damage. In most of the world, the unit is J/cm2, though.
    - MayeulC 4y ago
      Ah, all right, I understand if it's used to rate accumulated damage for incidents. For ongoing arcs, or comparing them however, I think it's a weird. A small arc, not even dangerous to touch, could have the same energy rating as a gigantic one if you measure the first over a year and the second over a millisecond.
closewith 4y ago
> You are forbidden by law (and mandated to report) such arcs in Europe. When you say in Europe, normally that refers to an EU Regulation or Directive (since other legislation varies wildly in member states). What are you referring to here?
- lima 4y ago
  Not sure why this comment was downvoted, I'm curious too.

by atoav 4y ago

vsnf 4y ago

> will they send you flying What is the mechanism by which an object would be propelled when hit by such an arc?

ars 4y ago
The heat of the arc rapidly expands air (like a lighting bolt), the heat of the arc also vaporizes the metal conductor, and the vaporized metal expands rapidly, and enormously. It's basically a small explosion. The hot metal then ignites in air adding even more heat to the explosion.
mediaman 4y ago
There is an explosive heating of air that’s like a bomb going off.
schoen 4y ago
Apparently mainly air pressure: > 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-arc-blast 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.

Semaphor 4y ago

> You are forbidden by law (and mandated to report) such arcs in Europe. You are forbidden by law to have an accident? This misunderstanding is probably because of my lack of knowledge, but what do you mean? > And trying to extinguish such an arc can be quite a challenge. I only read about them in this thread, so I’m probably missing something again, but isn’t it an instantaneous thing and not something you need to extinguish?

c_o_n_v_e_x 4y ago
>You are forbidden by law to have an accident? This misunderstanding is probably because of my lack of knowledge, but what do you mean? 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.
Doxin 4y ago
You are forbidden by law to have an accident of this nature. Yes. If you do cause an accident of this nature you are criminally negligent no matter the circumstances leading up to the accident because it's your duty to ensure it doesn't. 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.
- chrisseaton 4y ago
  Doesn’t make having an accident illegal make it more likely that people won’t report the accidents and won’t learn and improve?

c_o_n_v_e_x 4y ago

Arcs are rated by calories per square centimeter. There's a lot factors that go into arc ratings, more than just voltage. To give a frame of reference, a flame from a lighter on the tip of your finger for 1 second is considered 1 calorie. Arc flash PPE ratings start at 4 calories and can go above 100. The high cal rated PPE does indeed look like bomb squad gear.

MayeulC 4y ago
It's weird to rate it in calories (∝ joules, W.s) instead of Watts.
- closewith 4y ago
  Energy is used rather than power as it's the cumulative effect in energy incidents that causes damage. In most of the world, the unit is J/cm2, though.
  - MayeulC 4y ago
    Ah, all right, I understand if it's used to rate accumulated damage for incidents. For ongoing arcs, or comparing them however, I think it's a weird. A small arc, not even dangerous to touch, could have the same energy rating as a gigantic one if you measure the first over a year and the second over a millisecond.

closewith 4y ago

> You are forbidden by law (and mandated to report) such arcs in Europe. When you say in Europe, normally that refers to an EU Regulation or Directive (since other legislation varies wildly in member states). What are you referring to here?

lima 4y ago
Not sure why this comment was downvoted, I'm curious too.