[Paul Anderson]

Paul Anderson asked the Naked Scientists:

I heard of cows or sheep which were in paddocks under high power lines giving birth to still born.
   
 Each night a lot of us sleep with an electric alarm clock near our head. The alarm clock will have a transformer converting 240v to 9 or 6v and that transformer works uses electromagnetic waves. Could the proximity to our heads be detrimental to our mental health?
   
Regards
Paul
NZ

What do you think?

[Pumblechook]

1. Many studies can find no evidence of any risks from e-m fields at any frequency.  The press tend to latch on to studies which say there 'may' be risks.   "Study finds no risk..."  is a headline you never see.

2. There wont be much of a field from balanced transmisson lines..  The field from one conductor will be largely concelled out by the field from another conductor with current flowing in the opposite direction.  Put more technically the vector sum of three equal (120 degree phase shift between them) fields from 3 phase transmission lines is zero.

3. There will a very very low field from a transformer which has a closed magnetic circuit.

4. Some studies have suggested that corona may account for of the alledged risks but I don't think that extends too far from the conductors and only applies to very high voltage lines.

5. There must be many thousands of places in the world where sheep and cows graze under power lines and a no higher than normal occurence of still birth. 

[Soul Surfer]

Electric magnetic and electromagnetic fields at strengths normally encountered in everyday life do not cause any significant harm  if they did it the epidemiplogy would be clear as it is with ionising radiation like alpa beta and gamma rays.  Obviously big electrical discharges can kill and khigh intensity electromagnetic fields can cook you like a microwave but these are not encountered in normal life within the known safe limits.

[lyner]

It would appear that em fields harm your health only when you can actually see the overhead cables which are carrying the current.
When you  are cooking or sitting next to your electric fire you are fine. When the cables are running through the walls of your house you're OK.
There must be a reverse placebo effect at work.

I do have a theory that overhead cables are most common in the less healthy parts of town, usually. The better-off citizens (= statistically healthier)  can afford to live in nicer surroundings. There could be a correlation although not a causal relationship.

[LeeE]

Living organisms are able to absorb em radiation, so there is potential for those organisms to be changed, and therefore potentially damaged, by any radiation they absorb.

However, the evidence shows that damage to organisms by exposure to em radiation is not perfectly linear between different subjects, different subject types, or even different occasions - that is, the likelyhood of damage by em, of any particular strength or characteristics, is largely statistical.

The probability of damage being caused by your alarm clock is fantastically small but given enough subjects it is likely to happen somewhere, and because the number of cases will be so small it is very unlikely that any direct correlation would be seen.

Having said that, you are much more likely to suffer damage from cosmic particles or from radioactive gases seeping from the ground, which are the primary engines for evolution, than you are from an electronic alarm clock.

[techmind]

For normal 50/60Hz transmission lines, the electric and magnetic fields can be considered separately.

From 100kV lines, the electric fields at ground-level (c. 1000V/m) can approach the internationally-agreed safety limits, eg only a factor of 5 or so below the limits (which are probably set fairly conservatively anyway). The field won't penetrate the body (because it is conducting), and I understand the "symptoms" are primarily a tingling in the skin/hairs standing on end etc. This may cause "stress" in the animals, but has little direct physical consequence. You can get electric fields which exceed 1/5th of that under the power lines simply in close proximity (ie less than 1m) from household electrical items - especially if they are plastic "double-insulated" items like radio/CD players. Earthed metal appliances like computers should have negligible electric field.

Pylons will also generate a magnetic field, which scales with the load (current) in the lines. For 100kV lines (180MW total max load) this field (c. 0.7uT) is much further below the corresponding safety limits and in fact is comparable to that deliberately generated by "T-loop" systems for the hearing-impaired. The magnetic fields close (less than 50cm) to a piece of consumer equipment containing a transformer or electric motor will be significantly higher (but still well-below recognised guidelines).

For more info (fairly tech) see the ICNIRP guidelines:
http://www.icnirp.de/documents/emfgdl.pdf

[lyner]

'Safety Limits' are only arrived at as a result of the analysis of recorded damage and health impairment. You can't do experiments on humans (except when they do it to soldiers and prisoners - naughty).
The opinions in this thread come from the same sort of data that is the basis for the internationally agreed safety standards. In effect, you are using a 'political' assessment of the same data to justify what we would hope should be non-biassed and totally objective (this is TNS, of course) view of the subject.

[daveshorts]

There have also been some quite elegant studies done on people who claim to be electro-sensitive - apparently they get headaches etc when exposed to electromagnetic fields...

The researchers put them in a room with apparatus to apply electromagnetic fields. The researchers then turned the coil on and off at random, and got the 'sensitive people' to note when they felt the symptoms... There was no correlation between the fields and the symptoms...

[Karen W.]

I always heard that it caused damage especially the electric blanket thing, cause I get cold easy, and large electric field areas..have been discussed like that for years...

Dave did your study prove no harm or just that they were not able to physically detect the electromagnetic field.. and just because they couldn't detect it.. did that mean health studies were not carried out.. I don't quite understand... could it possibly pose longer term harm physically weather they were able to say or not..?

[Pumblechook]

I did see a TV test where people who claimed to feel ill when near mobile phone masts were put into a hotel and a temporary mast was set up in the car park.  Some did indeed did fell ill one so badly he couldn't stay.  Up to that point the mast hadn't been powered.

A much more scientific and more extensive test  found that people who claimed to be electrosensitve could not tell if a similated mobile phone next to head was 'off', 'radiated plain carrier' or 'carried normal mobile phone signals'...   Conducted by one the London University colleges and published by the BMA.