Silly Question : HERF

[swen_out_west]

Being in the Navy for 20 years and all the Safety requirements that went with the Job as an Air Search Radar Maintenance Technician makes me wonder, especially, since you see warnings in CB manuals regarding transmitting by Gas Stations.

Is there any HERF (Hazards of Electromagnetic Radiation to Fuels) / RADHAZ (Radiation Hazards) that I need to concern myself with, especially in regards to the big Propane Tank I have behind my house.

My biggest reason for asking this is that I am planning on putting up a 4 element Y-Quad directional in my backyard and when transmitting towards town the tank will be slightly in the path about 150 feet from the antenna. Just the thought of a 250 gallon propane tank being exposed to the EM field makes me uneasy.

I've tried to find a better spot to put the antenna, but with all my tin sheds and carports I really don't have any other place to put it.

I know this may be considered a stupid question, but I really have been dragging my feet on setting up this antenna because of not knowing.

 

[jonwienke]

Definitely not.

The tank is a Faraday caage shielding the propane from the RF.

And your power level is orders of magnitude lower than typical military radars. If you can stand next to your antenna without frying yourself, then you don't have to worry about igniting fuel.

 

[swen_out_west]

I figured that regarding power out but even HandHeld Radios in the Navy have a 100 foot restriction of radiation when it comes to ordinance and fuel handing operations.

I always figured that the HERF requirements were a little stringent in that regards, especially with the change over to less volatile fuels like JP-5, but like I say it made me wonder.

There is no stupid question right? Even though this one really was stupid, But like I say if the thought crossed my mind then I needed to at least ask someone. Then as my house is leveled I can say, 'that's a new one'. LOL

 

[jonwienke]

Ordnance is a little different than a tank of fuel. A blasting cap doesn't take a whole lot of energy to detonate.

 

[swen_out_west]

Ordnance is a little different than a tank of fuel. A blasting cap doesn't take a whole lot of energy to detonate.

I totally understand erring on the side of caution when it comes to HERO (Ordanance) (especially having done one duty assignment with an EOD unit) and pretty much think that most of the modern day HERF (Fuel) requirements is just to keep a standard.

After all, the guys onboard the MSC refueling tankers don't seem to have to follow the same restrictions as the regular Navy. You see them transmitting on their handhelds during refueling operations all the time. The only restriction they really impose is the securing of radars and that's more of a HERP (Personnel) requirement than anything.

 

[swen_out_west]

Appreciate the affirmation of what I thought, Really shouldn't have even asked it, if anything I was just looking for a conversation starter even if it made me look stupid.

 

[mmckenna]

At 4 watts, there is little energy involved. Even with a directional antenna you are probably losing a fair amount of power in your coaxial cable.

I agree with what Jon says. Little risk involved.

The FCC does have some rules for maximum exposure limits and the like, but they usually do not come into play until you are up around 100 watts or more. Technically some amateur radio installation would fall under the rules.

 

[mmckenna]

Appreciate the affirmation of what I thought, Really shouldn't have even asked it, if anything I was just looking for a conversation starter even if it made me look stupid.

Nah, it's a good question.
As you know, the military tends to over react to many possible and imagined risks. I remember going aloft once to fix a halyard that had jammed in one of the blocks. Even though we were in port and everything was shut off, they still had to go through all the procedures to lock out transmitters and radars. Funny part was if I was on one of the small boats, I would have been running around with a marine radar a few feet from my head with no concern.

Even at 50 watts on GMRS, you should be careful.

 

[swen_out_west]

At 4 watts, there is little energy involved. Even with a directional antenna you are probably losing a fair amount of power in your coaxial cable.

I agree with what Jon says. Little risk involved.

The FCC does have some rules for maximum exposure limits and the like, but they usually do not come into play until you are up around 100 watts or more. Technically some amateur radio installation would fall under the rules.

Ummm..... Ok.

But "hypothetically" speaking, if the radio were to put out 25 watts in SSB mode into a 9.9 db gain antenna, That is an ERP of 244 watts, thus the reason it even crossed my mind.

On that hypothetical calculation, it's small potatoes compared to some of the rigs out there. Considering that most houses outside of cities are fueled by propane and some guys are pushing 500 watts of power out (One even is a Ch6 Superbowler), without even taking into consideration their ERP, therefore it made me wonder.

 

[mmckenna]

Ummm..... Ok.

But "hypothetically" speaking, if the radio were to put out 25 watts in SSB mode into a 9.9 db gain antenna, That is an ERP of 244 watts, thus the reason it even crossed my mind.

True, but that would be highly focused and unless you purposely pointed it at your LPG tank, very little of that energy is going to reach it.
And, as Jon said, the tank is all metal and all the lines are metal. It's all grounded. Where you would have an issue is;
1. you had a leak with enough fuel/oxygen to create a flammable/explosive mixture, and had that pooled in the right location.
2. Part of the system not grounded and something of a gap to create a place where a spark could happen.

Even with all that, the hot and dry winds you get down there probably make static electricity a bigger risk than a CB, even with 244 watts ERP.

If everything is done per code, you probably wouldn't have an issue. That would mean everything is properly grounded. There are no gas leaks. No place where gas/air can accumulate with an ignition source, etc.

On that hypothetical calculation, it's small potatoes compared to some of the rigs out there. Considering that most houses outside of cities are fueled by propane and some guys are pushing 500 watts of power out (One even is a Ch6 Superbowler), without even taking into consideration their ERP, therefore it made me wonder.

Those levels of power might be some more concern, but there would still need to be a mixture of air and fuel plus the ignition source. RF on it's own isn't an ignition source. You'd have to have something conductive to receive that energy and make a spark with it. You'd really have to put a lot of work into making that happen. Simply having an LPG tank and a two way radio isn't enough.

Now, add in a few hundred watts with an antenna that's too close to the ground. Throw in a bunch of rusty barbed wire to act like an antenna, the rust to make a diode, maybe a spark from all that, just the right mixture of fuel/air, no wind, not raining, low humidity, etc. and then you could probably make it happen. Years ago MythBusters did a whole episode on the cell phone/gas pump thing. As I recall they were not able to trigger a fire or explosion. They even went as far as to build an enclosure, fill it with the right air/fuel mixture, place a cell phone in side there and make calls, call the phone, etc. Nothing happened. I do think they finally go frustrated and set off something in the space to force an ignition. Only then did they get an explosion.

I've been at a lot of radio sites, even a few with no utility tie in. The site was 100% solar and LPG generator. Lots of high power stuff up there, cellular, LMR, microwave, etc. No issues.
I've been at other sites that had LPG tanks and a small thermo electric generator producing a few watts of power to run equipment that transmitted occasionally, again, no issues.

The issues at these sites isn't RF triggering an ignition of fuel. It's usually someone with a rifle or vandals.

 

[swen_out_west]

Even with all that, the hot and dry winds you get down there probably make static electricity a bigger risk than a CB, even with 244 watts ERP.

If everything is done per code, you probably wouldn't have an issue. That would mean everything is properly grounded. There are no gas leaks. No place where gas/air can accumulate with an ignition source, etc.

.....

Years ago MythBusters did a whole episode on the cell phone/gas pump thing. As I recall they were not able to trigger a fire or explosion. They even went as far as to build an enclosure, fill it with the right air/fuel mixture, place a cell phone in side there and make calls, call the phone, etc. Nothing happened. I do think they finally go frustrated and set off something in the space to force an ignition. Only then did they get an explosion.

.....

If I recall the lady that ignited while at a gas station had more to do with her sweater and sitting in her car talking on the cell phone than anything. The static potential then caused a spark when she touched the nozzle. Right where the fumes while pumping gas is the most prevalent.

On that note, my uncle used to have a cigarette while gassing up, he just kept it away from the nozzle, lol... But it did teach me that the smell of gas fumes has nothing to do with fuel/air mixture. He's also the one that taught me at age 12, you can extinguish a lit match in diesel.

 

[mmckenna]

Yeah static is an issue with cars since they are isolated. Commercial fueling trucks used in the construction industry, LPG vendors filling up tanks, etc. will always run a ground lead and ground the truck before anything, or at least the are supposed to.

Usually what's a bigger issue in radio facilities is improperly maintained and improperly charging storage batteries outgassing hydrogen.
I recently have been upgrading my telephone switch sites, including new battery systems. Part of the code requires us to install hydrogen sensors in all the rooms where the batteries are. If I'm doing my job right and our power systems are operating as designed, and none of the safety's have been bypassed, there isn't any reason for those battery systems to ever outgas hydrogen. Still, I'd not want to be around if things when wrong.

 

[swen_out_west]

Yeah static is an issue with cars since they are isolated. Commercial fueling trucks used in the construction industry, LPG vendors filling up tanks, etc. will always run a ground lead and ground the truck before anything, or at least the are supposed to.

Usually what's a bigger issue in radio facilities is improperly maintained and improperly charging storage batteries outgassing hydrogen.
I recently have been upgrading my telephone switch sites, including new battery systems. Part of the code requires us to install hydrogen sensors in all the rooms where the batteries are. If I'm doing my job right and our power systems are operating as designed, and none of the safety's have been bypassed, there isn't any reason for those battery systems to ever outgas hydrogen. Still, I'd not want to be around if things when wrong.

That's actually a real concern. I've had the misfortune of being around someone, when I was a teenager, when a truck battery exploded, due to excessive cold cranking and most likely sparking the jumper leads right by leaking caps of the cells Since it was winter time and in the middle of a frozen lake we used snow to flush him as best we could, after he stripped his clothes that had been drenched with acid. After thoroughly scrubbing his exposed skin ie: face and hands with snow, we put him in another vehicle that had the heater going and rushed him to town for a complete shower and new clothes. Luckily the only damage was his brand new parka and a small chemical burn on the top of one of his hands.

 

[mmckenna]

Dang, that's scary.
I did walk into a radio site once that had the backup batteries charging at way to high a voltage. Took me a second to realize what I was looking at. The cell caps from the top of the battery were shot across the room. Acid had leaked out, etc. A real mess, but no one in the room at the time. When I checked the power supplies, they were running about 15 volts into a 12 volt battery that should have been charging at about 13.6.
Needless to say, it's little things like this that we learn from.

 

[jonwienke]

tl;dr static electricity is a far bigger fire/explosion risk than RF, unless you're running RF power in the kilowatts or more. And if you're managing static electricity, then you're also protecting against stray RF-induced sparks.

 

[swen_out_west]

I remember going aloft once to fix a halyard that had jammed in one of the blocks. Even though we were in port and everything was shut off, they still had to go through all the procedures to lock out transmitters and radars.

One of the biggest reasons for going aloft when some ships first pull into port is the close proximity of the SPS-55 navigational radar antenna to the signal flags, lol.

As the 49 tech I went aloft most of all the ET's, and my radar is the biggest HERP danger onboard ship, so I had the proud distinction of being the lead tech in charge of securing and hanging the tagouts/lockouts, good stuff shipmate.

But I also had my signature all over the man aloft qualification on my CG and we used to screw with JO's alot. lol Touching the top of the TACAN antenna was part of my conditioning of getting over the fear of heights as part of that qual, lol. Not too mention, all that way up and reaching out for it gave me a good opportunity to observe and teach.

 

[krokus]

Touching the top of the TACAN antenna was part of my conditioning of getting over the fear of heights as part of that qual, lol. Not too mention, all that way up and reaching out for it gave me a good opportunity to observe and teach.

Went aloft with a guy who was afraid of heights, on a carrier. He did not take well to me jumping up and down, to show how sturdy that upper yardarm was.

Back to the OP, HERF is not an issue for your setup, unless you are running a lot of power, or your antenna is laying on the ground. Even then, you would need just the right mixture of circumstances. (As others have mentioned.)

Sent via Tapatalk

 

[FiveFilter]

QUOTE: "But "hypothetically" speaking, if the radio were to put out 25 watts in SSB mode into a 9.9 db gain antenna, That is an ERP of 244 watts, thus the reason it even crossed my mind."

Is that the way the "db gain" factor of an antenna works? I thought it meant the increased receive of an antenna as compared to some factor, such as compared to another antenna or a standard of some sort. I didn't realize it means an antenna can magnify the radio signal energy by the equivalent value of the stated db factor.

 

[mmckenna]

Sort of.

It increases the ERP (Effective Radiated Power) by using the antenna design to focus the RF power into a specific plane or direction.

Higher gain mobile and base vertical antennas do this by focusing the radiated RF towards the horizon, or in some cases, a bit below the horizon (called "downtilt).

Directional antennas, like the Yagi design, do this by focusing most of the power in one direction. While the amount of RF energy is the same, it's just directed more in specific directions.

Usually the gain numbers are shown as dBd or dBi:
dBd = Decibels compared to a dipole
dBi = Decibels compared to an isotropic radiator

It's important to look at the letter after the dB to see what they are actually talking about. Some sneaky antenna manufacturers will simply quote them as dB. That's basically comparing it to an unknown, which lets them claim whatever amount of gain they want.

Quarter wave mobile or base antennas are -usually- considered a 0dBd

There is a good simple explanation here:
http://www.pulseelectronics.com/docs/library/Antenna Basic Concepts 07 12.pdf

 

[RFBOSS]

In basic function, gain type antennas work by capturing the omnidirectional energy radiated by an antenna and focusing it to a single point. Somewhat like using a magnifying class and sunlight to start a fire.

The following antennas are modeled in 4nec2 software, not the most accurate, but good enough for this example.

The first picture shows the pattern of a VHF omnidirectional antenna. Note how the energy spreads out in all directions.

The second picture is of a VHF gain type antenna (Yagi). Note how the energy in now focused in mostly one direction. The additional elements of the antenna have captured the energy (signal) and focused it in one direction. The physics of this can be somewhat complicate, but this is basically how it functions.

The actual pattern will vary with the design of the antenna, but this is a good example.

This applies to the antennas whether receiving or transmitting.



The gain in dB will be listed as dBi (gain referenced to an theoretical point source) or dBd (gain referenced to a dipole antenna). For the same real world gain, the gain listed as dBd will be numerically about 2.1 db thess than the gain in dBi.