Actually, the fundamental measurement of radiation is the electron volt. Gamma rays are measured in eV, although the higher the eV is, the shorter the wavelength and the higher the frequency. As the frequency increases, the energy increases. The threshold where the frequency becomes ionizing occurs at the UV range, ie it has the ability to strip electrons from atoms, about 10 eV, or 2,500 Terra Hertz (120 nanometer wavelength). This, you will note is independent of the amplitude of the wave. Since an emp is a function of both amplitude and frequency, a nuke emp has a lot of high extremely high frequency components, which means they can contain a lot of x-ray and gamma ray energy. I believe there is a formula for converting eV to RAD (Radiation Absorbed Dose), which can then be converted to REM (Rad Equivalent Man), which takes into consideration the type of exposure. It's been a few years since the college Rad Health Physics class I took, so I don't know the specific formulas anymore, but they are out there (I think it is 1 Rad =6.24E7 MeV, or 62.4 trillion electron volts). There is a table that shows what damage occurs to the human body at different REM doses. I believe the first to go are the crypt cells of the small intestine at something like 50 REM, then the marrow, and so on. Lethal doses aren't immediately lethal, so a 300 to 500 REM dose takes time to kill, whereas a 5,000 REM dose is going to shut you down before you can take a couple steps. Here's a link to an industry standard exposure table, which has the LD 50/50 actually slightly lower than you noted:

http://www.pimahealth.org/dmat/dmat_radiationchart.pdf

Basically, if you are close enough to hear the bright blue arcs going between the two PU spheres, you are toast before you can get out of the room.

The statement that you have to be attached to a very large conductor to be effected by an EMP is limited to the size of the field you are exposed to. If the field you are exposed to is intense enough, you don't need to be attached to anything and you will be cooked.

Here's another aspect to consider about popping a conventional EMP (forget the nuke aspects for a moment, let's just use non-ionizing fields). EMPs generate high momentary electromagnetic/electrostatic fields. Having induced emf fields using large coils, I can tell you that if the field is high enough, it can have nasty effects on the musculo-skeletal system. We had a coil that we put tools in to magnetize by pulsing the coil with a high voltage transient. We experimented with animals using this field and found out that the pulse at a close proximity fairly turned the critter (which was not electrically connected to the coil in any way) inside out!!! Now, while it's not likely that people will be that close to the source, it is important to note that the field we were creating was not nearly as big as the tactical EMPs we've been talking about here. Even at that, the coil blew an electrically isolated DMM up from over three feet away.

Another experiment used a cascading voltage multiplier to bump line voltage up to about 115kv. We called it the symphony box, because it made beautiful arcing noises if you moved the probe near any equipment that the return was clipped to. We clipped the return on a piece of equipment and without even arcing the probe we could just wave the tip around inside the chassis and all the semiconductors would blow. It was a good way of decommissioning some piece of junk that an owner wanted us to resurrect for more than the thing was worth. Some people just can't be convinced otherwise.

Nuke EMPs do contain an ionizing component, which has to be considered as part of the whole effect. Propagational loss due to high altitude detonation is likely going to keep them from generating a significant instantaneous dose, but it is still there. Likewise, propagational loss keeps the amplitude component from generating an acute biologic effect as well.

The bottom line is REM and eV are not two completely different critters. If it were, then there would be no such thing as ionizing rays, like UV, X-Ray and Gamma. EMPs do pose a health risk if the relative intensity of the exposure is high enough, regardless of the grounding potential of the individual exposed.

There's an awful lot of this sort of information on the internet, so I won't go any deeper (heck, I've probably walked off the deep end already). Do some more research if you really want to know, but I classify such information as "nice to know" trivia. <img src="/images/graemlins/grin.gif" alt="" />