Or are we completely non-magnetic?
Those aren’t mutually exclusive. I’m not really sure if they could be harmful, but humans aren’t non-magnetic. Water is diamagnetic which means in the presence of a magnetic field it exhibits a response. I’ve seen spiders and frogs levitated and I pushed grapes around a table in a college physics class. I’m not sure what the question is, I guess you could slama person into a wall or something like that with a strong enough magnet, but I’m unsure if the field itself would mess with you. I’d think it would, but that’s just a gut feeling.
Also keep in mind that there’s another variable of equal importance: frequency.
An old physics teacher of mine used to work with superconducting electromagnets. He said that one had to to walk extremely slowly around the lab, otherwise the the magnets would induce currents in the brain that could cause unconciousness. I don’t think these magnets could cause any permanent damage though.
This happened to a friend of mine.
At the time, he was working as an industrial electrician at GM. He was working on the semi-big stuff: 600-volt three-phase lines, the kind where if you drop a screwdriver across them, it vapourises in a flash of plasma.
One day he and his buddy had to repair a transformer. They shut off the power that fed it, and locked it out, placing a red warning tag and a lock to prevent anyone from physically moving the switch to turn the power back on.
Then they went down inside it. Electrical transformers are essentially massive pieces of metal wound with wire; they use magnetic fields to transfer energy between electrical circuits. This one was large enough that a couple of men could go inside it, with metal walls and wire on all sides.
Suddenly they noticed that the walls were humming. The power was on. They could not get out, because the opening was small. They would have touched various live parts of the transformer and been instantly killed. They had no choice but to yell and scream for forty minutes until someone heard them and shut the power off again to rescue them.
It turned out that another worker had cut the lock and turned the switch to restore power to his own section, not thinking that connected equipment might be under repair or the act might affect someone else. I presume that worker was fired immediately at the very least.
My friend and his buddy were off work for two weeks because the intense magnetic field inside the transformer had made them ill.
You mean they went near a critical distribution component without having a permit to work certificate ?
Sorry but simply sticking a lock in place is not enough.
I presume they had all the required documentation.
Even if they didn’t, lockout/tagout procedures are in place for a reason, and anyone who violates them needs to be fired and possibly prosecuted. No certificate is going to protect someone from a dumbass who thinks lockout/tagout doesn’t apply to him.
Or maybe the idea that they spent an hour in a nearly fried condition made them ill. I would be somewhat hesitant to come back to work. I also might be a bit tempted to beat the living sh** out of the guy who cut the lock.
When you have people working in a confined space, its common sense to have someone on the outside observing, and in the UK it would be considered a legal requirement.
I still cannot believe that someone would be so stupid as to rely completely on a locked out switch, and the reason has been very well demonstrated.
The proper thing is to completely withdraw the breaker unit and replace it with a dummy that is locked in place,or it would be to remove links or fuses (and replace with bright red dummies) and lock up the fuses or links in a container away from the working area. Access to the working area must be restricted only to those carrying out - or directly involved in the work.
You would also have danger signs posted.
You would also have regular supervision by patrolling senior engineers to ensure that the conditions of the permit to work certificate are being maintained.
Sorry, but these guys were asking for it.
Electrical working permits, lockout procedures, etc. are relatively recent developments in electrical services. Every time there is a new incident there is a tendency to write new, tighter procedures to prevent a recurance.
I worked where there was a big DC electomagnet. It would grab the nails in your shoes and pull your foot to one of the poles. (Nails were used in shoes years ago in case you wanted to ask.)
A superconduction copper container placed between the poles was difficult to control by hand.
I’m only a young 'un I guess, having only worked in the electrical industry for 30 years - started in '76, but such precautions have certainly been absolutely unexceptional all that time.
Even if WE are, you gotta worry about anything metalic in your body: meidcal screws & plates, pacemakers, shrapnel and as I understand it, even some tattoos. Just ask an MRI technician.
At the risk of deviating from the discussion on safety standards in the work place the following link indicates the latest generation of MRI machines for scanning human bodies are operating at magnetic flux densities of 1 T with some machines using 4 tesla.
There is a comment that says the 1T machine are safer than the 4T machines.
Anyway it gives as ref point that 1T seams to be OK.
http://hypertextbook.com/facts/1997/AllaReyfman.shtml
Don’t buy the guys in the transformer getting sick from the magnetic flux, I am not about to do the calculations but with the space volume involved and the added bonus of the iron core found in most large transformers pretty much contains the magnetic field, well it just does not add up.
The story about the super conducting magnets in the lab and scrambling the brain, no way. The field strength would fall off as 1/r2 (that is supposed to be one over r squared), just how feeking strong would these things be to affect someone walking around a lab.
anyway to try and anser the Op question, it would appear 1-4 T are ok.
Some magnetic resonance spectroscopy machines generate fields up to 12T
Also here at berkley they have taken some guidlines and simplified them
http://radsafe.berkeley.edu/nir1101e.html
seams the largest hazard is from flying metal objects
best regards
Not in the US.
OSHA’s lockout/tagout procedures do not call for swapping out circuit breakers or patrols by engineers.
The electricians in the transformer were entirely justified in believing they were completely safe. The only possible fault I’ve noticed was the lack of explanation if each man put his own lock on the disconnect, which is a requirement when more than one person is working on equipment.
1/r[sup]3[/sup] or faster, actually, unless they’ve discovered magnetic monopoles.
Sorry for reviving a long dead thread, but I wanted to make a comment on this:
Transformer cores form a closed loop. This means that any magnetic field generated by current flowing through the primary winding, will remain contained within the core.
Of course, some of the magnetic field will escape (fringe fields), but since these represent energy losses, transformers are designed so fringing is kept to a minimum.
So, even a big-ass medium voltage transformer will generate magnetic fields orders of magnitudes smaller than a MRI machine.
“Lock-out/tag-out” is a standard procedure when working on dangerous equipment. Seriously, you haven’t heard of this concept? I work at a glorified grocery store and we do this. It is in addition to any other paperwork/permit/permission you have.
You turn the power off, physically lock it, and put a tag on it. In industry in the US this is universally recognized as “as someone is working on this stuff, don’t touch”. ONLY the person who locked the box/switch/whatever should have the key and ONLY that person unlocks the power later.
Anyone who is such as tool as to cut off the lock should be first fired and the, in my opinion, prosecuted for reckless endangerment or something of the sort because that is very much putting the life of another being at risk.
Maybe you’ve never worked around such equipment and thus you are unfamiliar with this very common procedure, but honestly, if you were at work and saw something was physically locked and had a bright red tag on it you would just go ahead and remove it rather than asking someone “hey, what the hell is this all about?”
Note that this thread is getting on a decade old.
But yeah, from what I’ve read about OSHA regulations, you could be having anal sex with your coworker on the altar of a catholic church while listening to Nickelback, and that would still be less taboo than removing his lock. Dude needed to be fired.
That is a demented misreading of what he said.