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Ed Anderson
Joined: 10 Jan 2006
Posts: 475
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 Posted: Thu Jul 12, 2012 8:26 am Post subject: grounding procedures |
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I was once fueling my Rv-6A out of "Approved" plastic 5 gallon fuel container. I had a racing funnel with a paper filter cartridge in the center of the spout. It was a 60F low humidity day with no wind. I had done this many times before.
This time near the end of the 5 gallon container, I attempted to raise the bottom of the container higher to get the last of the fuel and broke connection between the funnel (also plastic) and the fuel container. There was a "Whomp" of ignition and I found myself with an event on my hands, to wit:
1. Holding a 5 gallon container with flames out its nozzle
2. Holding a large racing funnel with fuel soaked paper filter blazing way.
3. Haven been mildly started by the unexpected ignition event - I had stepped back a pace. This resulting in the funnel I was holding being pulled from the fuel tank leaving me with flames coming out of the aircraft fuel tank, flames on the wing surface where I dragged the emptying funnel from the wing tank opening and flames on the tarmac from that dripping from the wing.
The first thought after "oh S...t" was not too panic, after which I quickly
1. Walked approx 15 feet from the aircraft and set down flaming container and funnel.
2. Ran to my Van for my fire extinuisher - always stored under drives seat (could not located it)
3. Raced back to the aircraft and brushed off the surface fuel/fire with a rag.
4. Picked up the wing tank fuel cap and remembered thinking "..this always worked in science class!" ..slapped to fuel cap into the flaming opening -which fortuntately worked just like in highschool science class with test tube and cork.
5. Stomped out the small fire on the tarmac.
Fortunately no damage to anything but my nerves and the funnel and container.
Even though I had used plastic fuel containers for decades refueling lawnmowers, etc without ever having an incident - I never used anything but metal containers aftewards - however, I was later told that the the breaking of the connection permitted the liquid flow to generated a static potential difference and it would not have mattered if funnel and container had been metal - it was the breaking of the connection that apparently resulting in the conditions that lead to ignition.
FWIW
Ed
From: Robert L. Nuckolls, III (nuckolls.bob(at)aeroelectric.com)
Sent: Thursday, July 12, 2012 11:52 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: grounding procedures
At 08:46 PM 7/11/2012, you wrote:
| Quote: | soooooooooooo my tanks are grounded to my engine. am i safe to attach a wire from my fuel nozzle to my exhaust pipe or does the wire need to go to the tank filler neck? [that doesn't make sense to me]
bob noffs |
The word "grounded" is poorly understood and
in this discussion poorly used. As we've studied
in other conversations, having "lots of grounds"
can be deleterious to system performance in terms
of noised conducted from one system to another.
This static charge thing, like most studies of
physics is an energy management issue. We have
an energy source (motion between dissimilar
materials in close proximity), energy storage
(capacitance - proportional to surface area
of mass carrying a charge), potential pathways
for the two masses to exchange levels of charge,
series resistance of those pathways, and finally
open air gaps in the discharge path were a spark
might form that is surrounded by a flammable mixture.
The legacy hazard from which all these discussions
arise are grounded in the management of charges
stored on LARGE surface areas (air transport/military
aircraft and fuel trucks or underground fueling
systems. BIG numbers in terms of potential energy
to be released in that worrisome air-gap.
I'll refer readers to a couple of documents I've
posted to Aeroelectric.com at
http://tinyurl.com/7et4jj5
These two documents speak to 'modeling' the human
body for the purposes of carrying out standardized
tests for ESD vulnerability. Given the surface
area of adult humans to be on the order of 1.5 to
2 square meters, they are 'modeled' as 100 picofarad
capacitors. Further the ability to conduct a charge
off that 'capacitor' is limited by the average
conductivity of the body between the center of charge
and a discharge point (finger tip) which is modeled
with a 1500 ohm resistor. Now, charge the capacitor up
to various voltages up to 15,000 volts and you have
a repeatable means for generating antagonistic stresses
on some device to be tested for ESD immunity.
The machine model is similar but 200 picofarads and
1 ohm of series resistance. I.e., more surface area
and better conductivity.
Now, what might we think the model would be for a
B-747? LOTS of surface area and metallic structure
which provides very low series resistance. Static
charges between large masses can knock you on your
can.
Getting back to filling puddle jumpers from gas
cans or even fuel trucks . . .
The model for a plastic airplane might consider
a surface area on the order of 1000 picofarads
but what's the series resistance? It's an insulator
with hing series resistance. In my studies
with ESD testing I discovered that the WORST case
instances for testing to human body model (15KV)
VERY LITTLE of the potential energy was dissipated
at the victim . . . that 1500 ohm resistor dissipates
90 plus % of the energy. When dealing with things
like metal airplanes and fuel trucks, the machine
models are in force with something on the order of 1000-2000
pf each and VERY LOW series resistance. Connecting
them together before dragging out the hose MAY
NOT dissipate all their charges to zero . . . but it does
bring them TOGETHER in terms of voltage thus ELIMINATING
a potential of spark through a low series resistance.
I forget the structure of the airplane that started
this discussion but I think we were talking about a
non-conductive hose fitted to a fuel transfer pump.
In this instance, ADDING a low series resistance
conductor along the hose length only increases potential
for energy dissipation in a spark at the end of the
hose. Bringing a potential charge on the airplane and
fuel storage containers together is 99.9% of the
safety issue. Having a very large series resistance
in the potential ignition discharge path is another
risk mitigation move.
I've been reading lengthy discussions about fuel
transfer safety on OBAM aircraft for decades sprinkled
with hangar tales and speculative advice . . .
but never have I seen a study of the physics that
underlie the potential for an ignition accident.
Just consider the millions of cars that get fueled
by ding-a-ling drivers every day without blowing
themselves up. Yes, there are the expected 'news'
stories and security camera videos about the
occasional filling station fire. Shucks even the
Mytbusters made a show out of the notion that cell
phones can trigger explosions or fire.
But even the hallowed Mythbusters failed to
mention the physics . . . much less consider how
HARD it is to initiate an explosion under laboratory
conditions (re: explosion proofing tests on motors
we used to build at Electro-Mech).
Bottom line is that if you don't have a means to
bring the surface charge of a container to the same potential
as the surface of your airplane, then the SAME limitation
is in force for causing a spark at the opening of your
filler cap. I.e. if you can't get a spark at the connection
of a potential equalization wire at the exhaust stack of
your engine, you won't get a spark at the filler cap
either. Potentials generated by flowing fuel are
similarly limited in their ability to conduct the
charge to a 'arc gap'. Consider that the fuel
is in constant motion so any charge the liquid carries
is being continuously dumped into the tank . . .
Where is the 'conductor' that's going to bring
that charge to an arc gap? Flammable hydrocarbons
heavier than gasolines are used as medium for
cooling and INSULATOR in high voltage transformers and
capacitors.
Where does the energy come from, where is it stored,
what is the potential equalization path, what is
the series resistance of that path, is it possible
or even NECESSARY to effect an equalization of
potentials at some point AWAY from the filler cap?
Bottom line is that using the same care you would
exercise in filling your car, boat or lawn mower will
suffice to secure your healthy use of that machine.
Adding prophylactic features willy-nilly without
understanding the physics and design goals may
increase risk as opposed to reducing it. If the
truth were known as to root cause for the anecdotal
fuel transfer fires, most if not all would be due
to carelessness.
Bob . . . | Quote: |
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
|
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2195 / Virus Database: 2437/5127 - Release Date: 07/12/12 [quote][b]
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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com |
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Thu Jul 12, 2012 9:53 am Post subject: grounding procedures |
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Even though I had used plastic fuel containers for decades refueling
lawnmowers, etc without ever having an incident - I never used
anything but metal containers aftewards - however, I was later told
that the the breaking of the connection permitted the liquid flow to
generated a static potential difference and it would not have
mattered if funnel and container had been metal - it was the breaking
of the connection that apparently resulting in the conditions that
lead to ignition.
Interestingly enough, 'grounding' the airplane
would have probably not have changed the outcome.
Your particular air/fuel/ignition triad was
constituted within a mini-system outside and separate
from the airplane itself.
Bob . . .
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Thu Jul 12, 2012 11:51 am Post subject: grounding procedures |
|
|
Bob, I built this rig to fuel my little LSA. I built it mainly to get out of having to bend over and crawl under the wing to fuel, but it also gets me away from where the fuel is flowing. The tubing legs (titanium from Boeing Surplus!) provide grounding although I am going to take advantage of the advice offered here and install a copper wire to pick up any static from fuel flowing through the plastic pipe and run it out to the legs to ground that, too. Using stuff from my strategic supplies and plastic pipe and fittings from Lowe's the whole thing cost less than $10. The other precaution I use during fueling is to always have a size 20 fire extinguisher rated for flammable liquids right next to me.
Rick Girard
On Thu, Jul 12, 2012 at 11:05 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 04:44 AM 7/12/2012, you wrote:
| Quote: | --> AeroElectric-List message posted by: "toddheffley" <public(at)toddheffley.com (public(at)toddheffley.com)>
I was always doubted the importance of using a metal funnel until I fueled our champ on a dry day with a large plastic funnel. I was standing in the tire so I was also insulated. A charge built up strong enough to attract the hair on my arm to stand up toward the cowl. No Harm, No Foul. It was a warning to alter my behaviour before a really bad indecent occurred.
todd
|
Sure, while funnels provide a handy tool for control
of the flow of liquid, they add a piece of 'loose gear'
to the mix and expose a the surface of liquid flow
to the air (and funnel surface). The former increases
local concentration of hazardous vapor, the later increases
potential for building an electro-static charge (motion
of dissimilar materials in close proximity). Your body
became yet another surface on which generated charges
could collect. A hair-raising experience both literally
and for consideration of increased risk.
99.999+ of fuel transfers in the world are effected with
a nozzle extend into the fuel storage system. Most are
metallic and in contact with each other. The only
thing you can do to IMPROVE on this combination would
be to close the liquid motion off from the air and
potential for spillage by using some feature like I
suggested yesterday.
As a general rule, I would avoid the use of funnels.
Yeah, Lindbergh used 'em . . . even lined the funnel
with a chamois to absorb water. We don't read much
about aviators of yor setting themselves on fire
during a fueling accident but the risks were demonstrably
great.
Bob . . .
====================================
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Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
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JLuckey(at)pacbell.net
Guest
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| Posted: Thu Jul 12, 2012 2:36 pm Post subject: grounding procedures |
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Ed,
Your story scares the s**t out of me (I wonder if the same happened to you?) but thanks for sharing. After having the advantage of reading about your experience I think I would change the order of operations a little:
- Before starting refueling operations, make sure fire extinguisher is where I think it is – perhaps even set it nearby on tarmac
- get rid of flaming container in my hands – keep me from catching on fire
- replace fuel cap – keep my airplane/fuel tank from continuing to burn
- go for extinguisher
I think this will become my pre-fueling check-list.
One thing that I do when fueling from plastic containers is, before I start pouring, touch the airplane (metal airplane) near the fuel cap while holding the full fuel container in the other hand.
In my little mind this helps equalize any differences in potential among airframe, fuel container, & me.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Ed Anderson
Sent: Thursday, July 12, 2012 09:25
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: grounding procedures
I was once fueling my Rv-6A out of "Approved" plastic 5 gallon fuel container. I had a racing funnel with a paper filter cartridge in the center of the spout. It was a 60F low humidity day with no wind. I had done this many times before.
This time near the end of the 5 gallon container, I attempted to raise the bottom of the container higher to get the last of the fuel and broke connection between the funnel (also plastic) and the fuel container. There was a "Whomp" of ignition and I found myself with an event on my hands, to wit:
1. Holding a 5 gallon container with flames out its nozzle
2. Holding a large racing funnel with fuel soaked paper filter blazing way.
3. Haven been mildly started by the unexpected ignition event - I had stepped back a pace. This resulting in the funnel I was holding being pulled from the fuel tank leaving me with flames coming out of the aircraft fuel tank, flames on the wing surface where I dragged the emptying funnel from the wing tank opening and flames on the tarmac from that dripping from the wing.
The first thought after "oh S...t" was not too panic, after which I quickly
1. Walked approx 15 feet from the aircraft and set down flaming container and funnel.
2. Ran to my Van for my fire extinuisher - always stored under drives seat (could not located it)
3. Raced back to the aircraft and brushed off the surface fuel/fire with a rag.
4. Picked up the wing tank fuel cap and remembered thinking "..this always worked in science class!" .slapped to fuel cap into the flaming opening -which fortuntately worked just like in highschool science class with test tube and cork.
5. Stomped out the small fire on the tarmac.
Fortunately no damage to anything but my nerves and the funnel and container.
Even though I had used plastic fuel containers for decades refueling lawnmowers, etc without ever having an incident - I never used anything but metal containers aftewards - however, I was later told that the the breaking of the connection permitted the liquid flow to generated a static potential difference and it would not have mattered if funnel and container had been metal - it was the breaking of the connection that apparently resulting in the conditions that lead to ignition.
FWIW
Ed
From: Robert L. Nuckolls, III (nuckolls.bob(at)aeroelectric.com)
Sent: Thursday, July 12, 2012 11:52 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: grounding procedures
At 08:46 PM 7/11/2012, you wrote:
soooooooooooo my tanks are grounded to my engine. am i safe to attach a wire from my fuel nozzle to my exhaust pipe or does the wire need to go to the tank filler neck? [that doesn't make sense to me]
bob noffs
The word "grounded" is poorly understood and
in this discussion poorly used. As we've studied
in other conversations, having "lots of grounds"
can be deleterious to system performance in terms
of noised conducted from one system to another.
This static charge thing, like most studies of
physics is an energy management issue. We have
an energy source (motion between dissimilar
materials in close proximity), energy storage
(capacitance - proportional to surface area
of mass carrying a charge), potential pathways
for the two masses to exchange levels of charge,
series resistance of those pathways, and finally
open air gaps in the discharge path were a spark
might form that is surrounded by a flammable mixture.
The legacy hazard from which all these discussions
arise are grounded in the management of charges
stored on LARGE surface areas (air transport/military
aircraft and fuel trucks or underground fueling
systems. BIG numbers in terms of potential energy
to be released in that worrisome air-gap.
I'll refer readers to a couple of documents I've
posted to Aeroelectric.com at
http://tinyurl.com/7et4jj5
These two documents speak to 'modeling' the human
body for the purposes of carrying out standardized
tests for ESD vulnerability. Given the surface
area of adult humans to be on the order of 1.5 to
2 square meters, they are 'modeled' as 100 picofarad
capacitors. Further the ability to conduct a charge
off that 'capacitor' is limited by the average
conductivity of the body between the center of charge
and a discharge point (finger tip) which is modeled
with a 1500 ohm resistor. Now, charge the capacitor up
to various voltages up to 15,000 volts and you have
a repeatable means for generating antagonistic stresses
on some device to be tested for ESD immunity.
The machine model is similar but 200 picofarads and
1 ohm of series resistance. I.e., more surface area
and better conductivity.
Now, what might we think the model would be for a
B-747? LOTS of surface area and metallic structure
which provides very low series resistance. Static
charges between large masses can knock you on your
can.
Getting back to filling puddle jumpers from gas
cans or even fuel trucks . . .
The model for a plastic airplane might consider
a surface area on the order of 1000 picofarads
but what's the series resistance? It's an insulator
with hing series resistance. In my studies
with ESD testing I discovered that the WORST case
instances for testing to human body model (15KV)
VERY LITTLE of the potential energy was dissipated
at the victim . . . that 1500 ohm resistor dissipates
90 plus % of the energy. When dealing with things
like metal airplanes and fuel trucks, the machine
models are in force with something on the order of 1000-2000
pf each and VERY LOW series resistance. Connecting
them together before dragging out the hose MAY
NOT dissipate all their charges to zero . . . but it does
bring them TOGETHER in terms of voltage thus ELIMINATING
a potential of spark through a low series resistance.
I forget the structure of the airplane that started
this discussion but I think we were talking about a
non-conductive hose fitted to a fuel transfer pump.
In this instance, ADDING a low series resistance
conductor along the hose length only increases potential
for energy dissipation in a spark at the end of the
hose. Bringing a potential charge on the airplane and
fuel storage containers together is 99.9% of the
safety issue. Having a very large series resistance
in the potential ignition discharge path is another
risk mitigation move.
I've been reading lengthy discussions about fuel
transfer safety on OBAM aircraft for decades sprinkled
with hangar tales and speculative advice . . .
but never have I seen a study of the physics that
underlie the potential for an ignition accident.
Just consider the millions of cars that get fueled
by ding-a-ling drivers every day without blowing
themselves up. Yes, there are the expected 'news'
stories and security camera videos about the
occasional filling station fire. Shucks even the
Mytbusters made a show out of the notion that cell
phones can trigger explosions or fire.
But even the hallowed Mythbusters failed to
mention the physics . . . much less consider how
HARD it is to initiate an explosion under laboratory
conditions (re: explosion proofing tests on motors
we used to build at Electro-Mech).
Bottom line is that if you don't have a means to
bring the surface charge of a container to the same potential
as the surface of your airplane, then the SAME limitation
is in force for causing a spark at the opening of your
filler cap. I.e. if you can't get a spark at the connection
of a potential equalization wire at the exhaust stack of
your engine, you won't get a spark at the filler cap
either. Potentials generated by flowing fuel are
similarly limited in their ability to conduct the
charge to a 'arc gap'. Consider that the fuel
is in constant motion so any charge the liquid carries
is being continuously dumped into the tank . . .
Where is the 'conductor' that's going to bring
that charge to an arc gap? Flammable hydrocarbons
heavier than gasolines are used as medium for
cooling and INSULATOR in high voltage transformers and
capacitors.
Where does the energy come from, where is it stored,
what is the potential equalization path, what is
the series resistance of that path, is it possible
or even NECESSARY to effect an equalization of
potentials at some point AWAY from the filler cap?
Bottom line is that using the same care you would
exercise in filling your car, boat or lawn mower will
suffice to secure your healthy use of that machine.
Adding prophylactic features willy-nilly without
understanding the physics and design goals may
increase risk as opposed to reducing it. If the
truth were known as to root cause for the anecdotal
fuel transfer fires, most if not all would be due
to carelessness.
Bob . . . | Quote: | | href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-Listhref="http://forums.matronics.com">http://forums.matronics.comhref="http://www.matronics.com/contribution">http://www.matronics.com/c |
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Ed Anderson
Joined: 10 Jan 2006
Posts: 475
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| Posted: Thu Jul 12, 2012 2:56 pm Post subject: grounding procedures |
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|
I think I did require an underwear check, Jeff. Yes, thinking these things out before hand is certainly the way to do it - coming up with a check list during - is not recommended {:>).
Actually, after that, I almost always (99%) either have the fuel truck come out or hook up to an airport type fuel facility. Decided transporting and transferring fuel was something I just did not have to do.
It would probably never happened again - but, once is more than enough!!!
Ed
From: Jeff Luckey (JLuckey(at)pacbell.net)
Sent: Thursday, July 12, 2012 6:34 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: RE: grounding procedures
Ed,
Your story scares the s**t out of me (I wonder if the same happened to you?) but thanks for sharing. After having the advantage of reading about your experience I think I would change the order of operations a little:
- Before starting refueling operations, make sure fire extinguisher is where I think it is – perhaps even set it nearby on tarmac
- get rid of flaming container in my hands – keep me from catching on fire
- replace fuel cap – keep my airplane/fuel tank from continuing to burn
- go for extinguisher
I think this will become my pre-fueling check-list.
One thing that I do when fueling from plastic containers is, before I start pouring, touch the airplane (metal airplane) near the fuel cap while holding the full fuel container in the other hand.
In my little mind this helps equalize any differences in potential among airframe, fuel container, & me.
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Ed Anderson
Sent: Thursday, July 12, 2012 09:25
To: aeroelectric-list(at)matronics.com
Subject: Re: grounding procedures
I was once fueling my Rv-6A out of "Approved" plastic 5 gallon fuel container. I had a racing funnel with a paper filter cartridge in the center of the spout. It was a 60F low humidity day with no wind. I had done this many times before.
This time near the end of the 5 gallon container, I attempted to raise the bottom of the container higher to get the last of the fuel and broke connection between the funnel (also plastic) and the fuel container. There was a "Whomp" of ignition and I found myself with an event on my hands, to wit:
1. Holding a 5 gallon container with flames out its nozzle
2. Holding a large racing funnel with fuel soaked paper filter blazing way.
3. Haven been mildly started by the unexpected ignition event - I had stepped back a pace. This resulting in the funnel I was holding being pulled from the fuel tank leaving me with flames coming out of the aircraft fuel tank, flames on the wing surface where I dragged the emptying funnel from the wing tank opening and flames on the tarmac from that dripping from the wing.
The first thought after "oh S...t" was not too panic, after which I quickly
1. Walked approx 15 feet from the aircraft and set down flaming container and funnel.
2. Ran to my Van for my fire extinuisher - always stored under drives seat (could not located it)
3. Raced back to the aircraft and brushed off the surface fuel/fire with a rag.
4. Picked up the wing tank fuel cap and remembered thinking "..this always worked in science class!" .slapped to fuel cap into the flaming opening -which fortuntately worked just like in highschool science class with test tube and cork.
5. Stomped out the small fire on the tarmac.
Fortunately no damage to anything but my nerves and the funnel and container.
Even though I had used plastic fuel containers for decades refueling lawnmowers, etc without ever having an incident - I never used anything but metal containers aftewards - however, I was later told that the the breaking of the connection permitted the liquid flow to generated a static potential difference and it would not have mattered if funnel and container had been metal - it was the breaking of the connection that apparently resulting in the conditions that lead to ignition.
FWIW
Ed
From: Robert L. Nuckolls, III (nuckolls.bob(at)aeroelectric.com)
Sent: Thursday, July 12, 2012 11:52 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: grounding procedures
At 08:46 PM 7/11/2012, you wrote:
soooooooooooo my tanks are grounded to my engine. am i safe to attach a wire from my fuel nozzle to my exhaust pipe or does the wire need to go to the tank filler neck? [that doesn't make sense to me]
bob noffs
The word "grounded" is poorly understood and
in this discussion poorly used. As we've studied
in other conversations, having "lots of grounds"
can be deleterious to system performance in terms
of noised conducted from one system to another.
This static charge thing, like most studies of
physics is an energy management issue. We have
an energy source (motion between dissimilar
materials in close proximity), energy storage
(capacitance - proportional to surface area
of mass carrying a charge), potential pathways
for the two masses to exchange levels of charge,
series resistance of those pathways, and finally
open air gaps in the discharge path were a spark
might form that is surrounded by a flammable mixture.
The legacy hazard from which all these discussions
arise are grounded in the management of charges
stored on LARGE surface areas (air transport/military
aircraft and fuel trucks or underground fueling
systems. BIG numbers in terms of potential energy
to be released in that worrisome air-gap.
I'll refer readers to a couple of documents I've
posted to Aeroelectric.com at
http://tinyurl.com/7et4jj5
These two documents speak to 'modeling' the human
body for the purposes of carrying out standardized
tests for ESD vulnerability. Given the surface
area of adult humans to be on the order of 1.5 to
2 square meters, they are 'modeled' as 100 picofarad
capacitors. Further the ability to conduct a charge
off that 'capacitor' is limited by the average
conductivity of the body between the center of charge
and a discharge point (finger tip) which is modeled
with a 1500 ohm resistor. Now, charge the capacitor up
to various voltages up to 15,000 volts and you have
a repeatable means for generating antagonistic stresses
on some device to be tested for ESD immunity.
The machine model is similar but 200 picofarads and
1 ohm of series resistance. I.e., more surface area
and better conductivity.
Now, what might we think the model would be for a
B-747? LOTS of surface area and metallic structure
which provides very low series resistance. Static
charges between large masses can knock you on your
can.
Getting back to filling puddle jumpers from gas
cans or even fuel trucks . . .
The model for a plastic airplane might consider
a surface area on the order of 1000 picofarads
but what's the series resistance? It's an insulator
with hing series resistance. In my studies
with ESD testing I discovered that the WORST case
instances for testing to human body model (15KV)
VERY LITTLE of the potential energy was dissipated
at the victim . . . that 1500 ohm resistor dissipates
90 plus % of the energy. When dealing with things
like metal airplanes and fuel trucks, the machine
models are in force with something on the order of 1000-2000
pf each and VERY LOW series resistance. Connecting
them together before dragging out the hose MAY
NOT dissipate all their charges to zero . . . but it does
bring them TOGETHER in terms of voltage thus ELIMINATING
a potential of spark through a low series resistance.
I forget the structure of the airplane that started
this discussion but I think we were talking about a
non-conductive hose fitted to a fuel transfer pump.
In this instance, ADDING a low series resistance
conductor along the hose length only increases potential
for energy dissipation in a spark at the end of the
hose. Bringing a potential charge on the airplane and
fuel storage containers together is 99.9% of the
safety issue. Having a very large series resistance
in the potential ignition discharge path is another
risk mitigation move.
I've been reading lengthy discussions about fuel
transfer safety on OBAM aircraft for decades sprinkled
with hangar tales and speculative advice . . .
but never have I seen a study of the physics that
underlie the potential for an ignition accident.
Just consider the millions of cars that get fueled
by ding-a-ling drivers every day without blowing
themselves up. Yes, there are the expected 'news'
stories and security camera videos about the
occasional filling station fire. Shucks even the
Mytbusters made a show out of the notion that cell
phones can trigger explosions or fire.
But even the hallowed Mythbusters failed to
mention the physics . . . much less consider how
HARD it is to initiate an explosion under laboratory
conditions (re: explosion proofing tests on motors
we used to build at Electro-Mech).
Bottom line is that if you don't have a means to
bring the surface charge of a container to the same potential
as the surface of your airplane, then the SAME limitation
is in force for causing a spark at the opening of your
filler cap. I.e. if you can't get a spark at the connection
of a potential equalization wire at the exhaust stack of
your engine, you won't get a spark at the filler cap
either. Potentials generated by flowing fuel are
similarly limited in their ability to conduct the
charge to a 'arc gap'. Consider that the fuel
is in constant motion so any charge the liquid carries
is being continuously dumped into the tank . . .
Where is the 'conductor' that's going to bring
that charge to an arc gap? Flammable hydrocarbons
heavier than gasolines are used as medium for
cooling and INSULATOR in high voltage transformers and
capacitors.
Where does the energy come from, where is it stored,
what is the potential equalization path, what is
the series resistance of that path, is it possible
or even NECESSARY to effect an equalization of
potentials at some point AWAY from the filler cap?
Bottom line is that using the same care you would
exercise in filling your car, boat or lawn mower will
suffice to secure your healthy use of that machine.
Adding prophylactic features willy-nilly without
understanding the physics and design goals may
increase risk as opposed to reducing it. If the
truth were known as to root cause for the anecdotal
fuel transfer fires, most if not all would be due
to carelessness.
Bob . . . | Quote: | | href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-Listhref="http://forums.matronics.com">http://forums.matronics.comhref="http://www.matronics.com/contribution">http://www.matronics.com/c |
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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
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rdsafe2000(at)yahoo.com
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| Posted: Fri Jul 13, 2012 6:49 am Post subject: grounding procedures |
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WARNING FROM SHELL OIL COMPANY DO NOT DELETE, PLEASE READ
MUST READ, EVEN IF YOU DON'T OWN A CAR
Shell Oil Comments - A MUST READ!
Safety Alert!
Here are some reasons why we don't allow cell phones in operating areas, propylene oxide handling and storage area, propane, gas and diesel refueling areas.
The Shell Oil Company recently issued a warning after three incidents in which mobile phones (cell phones) ignited fumes during fueling operations
In the first case, the phone was placed on the car's trunk lid during fueling; it rang and the ensuing fire destroyed the car and the gasoline pump.
In the second, an individual suffered severe burns to their face when fumes ignited as they answered a call while refueling their car!
And in the third, an individual suffered burns to the thigh and groin as fumes ignited when the phone, which was in their pocket, rang while they were fueling their car.
You should know that: Mobile Phones can ignite fuel or fumes
Mobile phones that light up when switched on or when they ring release enough energy to provide a spark for ignition
Mobile phones should not be used in filling stations, or when fueling lawn mowers, boat, etc.
Mobile phones should not be used, or should be turned off, around other materials that generate flammable or explosive fumes or dust, (I.e., solvents, chemicals, gases, grain dust, etc...)
TO sum it up, here are the Four Rules for Safe Refueling:
1) Turn off engine
2) Don't smoke
3) Don't use your cell phone - leave it inside the vehicle or turn it off
4) Don't re-enter your vehicle during fueling.
Bob Renkes of Petroleum Equipment Institute is working on a campaign to try and make people aware of fires as a result of 'static electricity' at gas pumps.
His company has researched 150 cases of these fires.
His results were very surprising:
1) Out of 150 cases, almost all of them were women.
2) Almost all cases involved the person getting back in their vehicle while the nozzle was still pumping gas.
When finished, they went back to pull the nozzle out and the fire started, as a result of static.
3) Most had on rubber-soled shoes.
4) Most men never get back in their vehicle until completely finished.
This is why they are seldom involved in these types of fires.
5) Don't ever use cell phones when pumping gas
6) It is the vapors that come out of the gas that cause the fire, when connected with static charges.
7) There were 29 fires where the vehicle was re-entered and the nozzle was touched during refueling from a variety of makes and models.
Some resulted in extensive damage to the vehicle, to the station, and to the customer.
 Seventeen fires occurred before, during or immediately after the gas cap was removed and before fueling began.
Mr. Renkes stresses to NEVER get back into your vehicle while filling it with gas.
If you absolutely HAVE to get in your vehicle while the gas is pumping, make sure you get out, close the door TOUCHING THE METAL, before you ever pull the nozzle out.
This way the static from your body will be discharged before you ever remove the nozzle.
As I mentioned earlier, The Petroleum Equipment Institute, along with several other companies now, are really trying to make the public aware of this danger.
I ask you to please send this information to ALL your family and friends, especially those who have kids in the car with them while pumping gas.
If this were to happen to them, they may not be able to get the children out in time.
[quote][b]
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n520tx(at)gmail.com
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| Posted: Fri Jul 13, 2012 7:01 am Post subject: grounding procedures |
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I agree that cell phone usage while fueling a car is not wise (you
should be paying attention to the task at hand), this specific "Warning
from Shell" is an internet urban legend.
http://www.snopes.com/autos/hazards/gasvapor.asp
On Fri, 2012-07-13 at 07:49 -0700, Richard wrote:
| Quote: | WARNING FROM SHELL OIL COMPANY DO NOT DELETE, PLEASE READ
MUST READ, EVEN IF YOU DON'T OWN A CAR
Shell Oil Comments - A MUST READ!
|
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john.maccallum(at)bigpond
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| Posted: Mon Jul 16, 2012 3:09 pm Post subject: grounding procedures |
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Interesting read but I think largely urban myth. It is certainly possible to get a spark produced through rectification of RF by a bad joint in a wire or even sheet metal. That is the main reason you can not have a transmitter around explosives.
A Cell phone is just a fancy two way radio and it is connected to and talking to the Network whenever it is turned on. So it is possible for a cellphone to transmit without you doing anything.
Just having it in your pocket would be a hazard if we accept the urban myth.
For example, The led display turning on will not induce a static charge in anything.
I think it is much more likely those types of events described in the warnings are because of the types of clothes that people were wearing and that they were ungrounded until they touched something on the vehicle.
To be safe you should ground yourself and the vehicle before you take the fuel cap off.
I try to remember to touch the fuel hose to the car before I take the fuel cap off.
Cheers
John MacCallum
Sent from my iPad
On 14/07/2012, at 1:01, Ron Walker <n520tx(at)gmail.com> wrote:
| Quote: |
I agree that cell phone usage while fueling a car is not wise (you
should be paying attention to the task at hand), this specific "Warning
from Shell" is an internet urban legend.
http://www.snopes.com/autos/hazards/gasvapor.asp
On Fri, 2012-07-13 at 07:49 -0700, Richard wrote:
> WARNING FROM SHELL OIL COMPANY DO NOT DELETE, PLEASE READ
>
>
> MUST READ, EVEN IF YOU DON'T OWN A CAR
>
>
> Shell Oil Comments - A MUST READ!
>
|
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