Gun safe as a faraday cage

[Kindrox]

If you want to stop all EMP/Radio signals, you have to be INSIDE a sealed metal container. Rubber strips/paint on an ammo can is not a sealed metal container.

We have "screen rooms" at work and you won't get a cell phone call inside one. Since that is what I know, I'll use the "screen" moniker.

For practical reasons, our screen rooms are a metal can inside a metal can, but theoretically you may or may not only need one for nuclear-induced EMP protection (I don't know).

For true protection I do know you need two. One stops electric fields, the second stops magnetic fields induced from the electric current flowing on the outer can.

Our screen rooms are on the order of $100k and are about 10' x 12'.

We do have smaller screen 'boxes' but you can typically still get a cell phone to receive a call in one. There is something about physical size which makes larger screen "containers" more effective.

If your screen container stops a cell call, you can probably consider yourself protected as I know it is no easy feat.

The screen room does not "need" to be grounded to work. It is only for safety, so that you large metal cage does not get electified and "grounded" through you. Screen rooms work on the principal that you cannot have any net charge (electrons) inside a sealed metal ball. No net charge means no EMP pulse of electrons.

 

[230RN]

Pet Picayune Peeve (PPP):

a high rate of speed

Speed is the first derivative of position.

A "high rate of speed" would imply the speed is changing, which is the second derivative, No? Meaning "acceleration?"

Actually, to get it kinda sorta back OT, I was thinking of getting one of those fancy Nikon Laser IRT scopes.

Aha! A raison d'etre for this thread. Protection for all them there electronical shooting aids.

I woulda never thought of that because I'm an old phart who doesn't trust them electronicimator gizzies to advise me how high over the Prairie Rat to hold at my eyeball-determined (not laser-determined) range to the aforesaid Prairie Rat.

And doesn't trust anememomitrators to tell me how far off to hold for the wind.

Prefer to use "Kentucky Windage" and "Kentucky Elevationage."

'Course, the Prairie Rats don't shoot back.

 

[Cesiumsponge]

If I remember correctly Mythbusters did an episode on EMP's . They drove a car through a EMP burst. It killed the motor and major electronics on the car. But some of the smaller stuff still worked, can't remember exactly what but the wipers, windows, maybe the dome light still worked. The ignition was done.

Mythbusters is entertainment, not science.

 

[another okie]

I think that show was the one with the shaved head guy who claims to be a Navy Seal, not the one with the Hollywood stunt guys.

In either case, Cesiumsponge's description is correct.

 

[ilbob]

Grounding a Faraday cage does not improve its effectiveness with respect to EMP. that is a myth.

Any large piece of metal is commonly bonded to reduce the chances of some kind of ground fault resulting in a hot piece of metal someone might come in contact with.

 

[Im283]

whether Mythbusters is science or entertainment doesn't change the fact that there were still electronics on that car that worked.

I still would like to know about the RSC's keypad.

 

[Cesiumsponge]

whether Mythbusters is science or entertainment doesn't change the fact that there were still electronics on that car that worked.

If the test isn't scientific in nature, the results are dubious and not conclusive, nor scientifically sound. Cobbling something together that "may simulate EMP" is not the same as a device designed specifically with the impulse waveform and power levels to "simulate EMP".

Maybe of their tests are approximations and aren't entirely accurate. Many here have complained before about their Carlos Hathcock sniper scope shot and how their setup was flawed, making the results inconclusive.

RSC keypads aren't shielded...at least not consumer grade stuff. Induced voltages should be enough to short all those junctions on your silicon semiconductors.

 

[Owens]

Interesting discussion, even if somewhat off topic.

I always thought that a 'screen' room or Farady cage was in essence a big resonant choke, that formed a trap, routing RF energy to ground.

Ah, the joys of a mechanical lock!

 

[mekender]

if i remember correctly, the US DoD did a study on EMP shielding back in the 60s... what they determined then was that it was impractical to spend $10,000,000 on shielding that could be easily be negated by a $5000 nuclear weapon... it was more economical for them to use redundant backups that were located geographically far apart

 

[Cesiumsponge]

Just for reference, mil spec FF-L-2740A

test subjection subsections:

4.6.11 Electromagnetic pulse. The lock shall be installed in a Class 6 security file cabinet as decribed in federal specification AA-F-358. The installed lock shall be tested in 4 orientations at each field level: front-on, drawer closed; front-on, drawer open; side-on, drawer closed; side-on, drawer open. The lock shall withstand 10 pulses in each orientation. The lock shall be subjected to transient pulse illumination with electric field peaks within the range of 28 to 37 kV/m with a 1.5 to 3.0 ns risetime. After exposure at each field level, the lock shall operate normally.

4.6.12 Electrostatic discharge. The lock shall be mounted on the test stand described in 4.6.8.1. The lock dial shall be subjected to 5 electrostatic discharges of 250 kV. After exposure, the lock shall operate normally.

You can buy yourself a Kaba X-09 electronic lock that meets/exceeds FF-L-2740A, if you want to put one on your safe. I hope you have four figures to spend on the lock though.

 

[mekender]

problem is, an EPM can easily go above 1MV/m which would be way beyond what those were designed to protect against

 

[Cesiumsponge]

The field strength drops as the inverse cube of the distance. If you double the distance from the point source, the field strength drops by a factor of 8. If you're 10 times the distance, its 1000 times weaker, and if you're 100 times further, its 1 million times weaker. You weren't seeing megavolt induction in electronic gear when the effects of EMP were first seen. You would have to be very near to the source to see that type of electric field strength.

No gear is hardened to withstand MV/m field strength to my knowledge nor is it practically possible. You'd have to use exotic materials with high dielectric strength like strontium titanate or barium titanate which have physical properties making them impractical for use outside of capacitor plates. If you're detonating EMP weapons high up in the air, you're not going to see megavolts induced on gear on the ground.