Fire while refueling

[Dieselten]

CAO 20.9 4.1.1.

 

 

[Old Koreelah]

...I always felt better when walking barefoot.

 

 

[Bluey]

Charges that build up on metal items distribute themselves evenly over the surface of the conductor and are easily removed by earthing. Unfortunately non conductors do not behave in the same way. When they become charged the charges cannot easily move around on the item as they are non conductive (this of course is dependent on voltage as anything can become conductive if the voltage is large enough even plastic).

 

I just did a quick experiment to confirm this as the humidity today is lower than yesterday ~10%. I attached a set of jumper leads to the same drum I used yesterday and earthed it to my homes earth stake. I then used the hairs on my legs to charge the side of the drum by moving the drum back and forth along the hair. I had no trouble doing this with the drum attached to the earth. I know it was charged by the large deflection of the hairs on my legs as the drum was moved toward them (so I used the hair to both charge and detect that charge). I also then used my finger tips to produce tiny audible sparks as I moved them close to and made contact with the drum. I then attempted to discharge the drum by rubbing the palm of my hand over the surface of the charged area. The charge reduced but was not eliminated. I repeated the above procedure with and without the earth leads connected with no significant differences in the results. This demonstrated that the earth was not effective. See the attached image for my setup.

 

Now assuming that the earth I used was a valid earth as I would expect it to be, then the following conclusion can be safely made.

 

Conclusion: Earthing plastic fuel drums is ineffective.

 

So, the results seem to suggest that static build up on plastic drums during low humidity is common and difficult to discharge. What I don't know is at what humidity level does it become a serious issue? What I mean by this is at what point will a large enough charge occur that a spark is likely? And if so, how big does the spark have to be to cause a fire? What I can confidently say is the spark I heard yesterday was louder and bigger than any spark I deliberately created today.

 

 

 

[Head in the clouds]

I just did a quick experiment to confirm this ......

Good explanation, good experiment Bluey.

 

One way to 'wipe' a static charge off a plastic surface is to give it a wipe with a damp rag. Might be an idea to keep a small water bottle and a rag handy for dry days.

 

And shave your legs ...

 

 

[Bluey]

That is a top idea head in the clouds. The evaporating moisture will remove charge just as would happen on days of high humidity.

 

 

[Bluey]

I just tried it and it worked perfectly. I first showed that a charge could be induced on the drum using hair as before (no earthing). After I was satisfied that the drum indeed could be charged I then wiped the surface of the drum using a lightly damp cloth. Charging by the same method as before failed to induce any charge what so ever!

 

Just be sure to wipe the surface of the nozzle too if you use one.

 

 

[Guest Andys@coffs]

You know that saying Oils aint Oils.......

 

Well Plastic isn't plastic......

 

There are plastic fuel containers that are Red and there are containers that are black. It's my understanding that the black drums have carbon black added to the molten plastic and as such are more conductive than the drums that don't have carbon black added during manufacture......

 

That said, the nozzles for all the drums aren't black and its through them that the fuel moves........

 

I think the black ones are made by Rheem in Au to our standards...

 

Andy

 

 

[goflying]

i think by placing the jerry can on the ground is enough to create an earth, that's why in your experiment it made no difference. I could be wrong.

 

 

[dazza 38]

When I was in the RAAF, from memory we went - aircraft to ground, tanker to ground , tanker to aircraft and finally nozzle to aircraft. IRT earthing

 

 

[Guest Andys@coffs]

You know that saying Oils aint Oils.......Well Plastic isn't plastic......

 

There are plastic fuel containers that are Red and there are containers that are black. It's my understanding that the black drums have carbon black added to the molten plastic and as such are more conductive than the drums that don't have carbon black added during manufacture......

 

That said, the nozzles for all the drums aren't black and its through them that the fuel moves........

 

I think the black ones are made by Rheem in Au to our standards...

 

Andy

Actually Haighs now sell them (http://www.haigh.com.au/images/ProductImages/AAAA%20Oct%2006.pdf) ....and a red one and a yellow one and a green one....all to the same standard....so....I'll wander back to the box I jumped out of and.........

 

 

[Old Koreelah]

Good to see that Science is being applied! As well as adding earth cables (with crocodile clips) to my steel jerrycan, I will be carrying a damp wrag for the plastic one.

 

 

[Bluey]

i think by placing the jerry can on the ground is enough to create an earth, that's why in your experiment it made no difference. I could be wrong.

I had no trouble inducing a charge with the container on the ground. Remember, I used a red drum. It would be interesting to test the earthing properties of the black ones.

 

 

[Guest Andys@coffs]

Charges that build up on metal items distribute themselves evenly over the surface of the conductor and are easily removed by earthing. Unfortunately non conductors do not behave in the same way. When they become charged the charges cannot easily move around on the item as they are non conductive (this of course is dependent on voltage as anything can become conductive if the voltage is large enough even plastic).I just did a quick experiment to confirm this as the humidity today is lower than yesterday ~10%. I attached a set of jumper leads to the same drum I used yesterday and earthed it to my homes earth stake. I then used the hairs on my legs to charge the side of the drum by moving the drum back and forth along the hair. I had no trouble doing this with the drum attached to the earth. I know it was charged by the large deflection of the hairs on my legs as the drum was moved toward them (so I used the hair to both charge and detect that charge). I also then used my finger tips to produce tiny audible sparks as I moved them close to and made contact with the drum. I then attempted to discharge the drum by rubbing the palm of my hand over the surface of the charged area. The charge reduced but was not eliminated. I repeated the above procedure with and without the earth leads connected with no significant differences in the results. This demonstrated that the earth was not effective. See the attached image for my setup.

Now assuming that the earth I used was a valid earth as I would expect it to be, then the following conclusion can be safely made.

 

Conclusion: Earthing plastic fuel drums is ineffective.

 

So, the results seem to suggest that static build up on plastic drums during low humidity is common and difficult to discharge. What I don't know is at what humidity level does it become a serious issue? What I mean by this is at what point will a large enough charge occur that a spark is likely? And if so, how big does the spark have to be to cause a fire? What I can confidently say is the spark I heard yesterday was louder and bigger than any spark I deliberately created today.

What about your feet, were you in shoes, or barefoot?

 

I ask in that the movement of hairs tells us that there is a significant potential difference between you and the drum, what it doesn't tell us is if you were the one stripped of electrons, or the drum was. In other words was it you or the drum that was different WRT earth. Could you get a spark from your finger to the earthing lead? If you could then you were the one that held the charge not the drum....

 

Andy

 

 

[Bluey]

I Was wearing flip flops but that doesn't matter as the contact between the two items is what causes the charge build up in both. When contact was made the charge did not dissipate. A properly earthed item would remove charge from my body and not charge it as was observed as the two come into contact, something we all experience regularly in our day to day lives.

 

I did a less controlled experiment at the airport earlier today where I charged the drum on myself and then a friend also tested it on themselves. Same results.

 

Also, the movement of electrons depends on which item has a stronger tendency to attract electrons. Therefore, the exchange of charges can vary with the type of materials in contact. Sometimes an item may attain a positive charge and at others a negative.

 

 

[Guest Maj Millard]

Bit confusing ...I have been refuel ULs since 1984 with the red 20 lt fuel containers. In fact at least two of the three I current use I have probabily had since day one. I have used the black Mr Funnels now for about 20 years. I don't use bonding leads and have never had a problem.

 

In that time I have heard of two static-discharge incidences both on trikes. Is it the white plastic tanks on the trikes that are the problem ?.I do live in a high humidity area, however inland and during winter I have refuelled on low humidity, cool days also with no problems.

 

The only thing I would suggest in my favour is that I always put the full fuel containers on the ground for a period prior to lifting them up to refuel on the wing.

 

Obviously this cannot be a wide spread problem, as there is a lot of refuelling done with the red fuel containers, and not a whole lot of incidences really. I 'm thinking the white plastic fuel tanks on the Trikes are building up a high static charge as they are generally exposed to air inflight going past them. Are they grounded in any way ?........

 

If the red containers were the problem, wouldn't we be seeing more incidences ?....we all use them often, all over the country and internationally really.........Maj...

 

 

[Bluey]

It's easy to get this whole thing way out of proportion especially by me right now. As Maj has stated it is a very rare occurrence. Airborne have stated that they take no special precautions when fueling trikes and they've been around for decades and have flown many thousands of hours and refueled thousands of times without incident. The whole triking community would have probably accumulated somewhere in the order of a million hours in the decades of operation

 

and most have refueled as I have. In all, I count about 4 known incidents in that time including mine. Let's say another dozen exist that have not been reported and you have less 20 tops in the history of australian triking. That's 20 failures in at least hundreds of thousands of refueling events. Clearly, a whole range of events have to come together to cause a fire. Yesterday was one of those rare days when it all did.

 

 

[kaz3g]

Hi Maj

Just make sure you take them out of your vehicle and place them on the ground to fill them.

 

Kaz

[Guest Maj Millard]

 

Hi Maj

 

Just make sure you take them out of your vehicle and place them on the ground to fill them.

 

Kaz

Which I always do Kaz..................Maj......

 

[Bluey]

I just found this good article worth reading. Here's the link:

 

http://www.ccohs.ca/oshanswers/prevention/flammable_static.html

 

Bluey.

 

 

[Bluey]

I think the following procedure might work well:

 

Bond or earth funnel to trike,

 

Earth trike,

 

Wipe drum with damp cloth including nozzle. This will make the drum conductive and allow it to be effectively connected to an earth.

 

Charges built up in the flowing fuel should be the only possible ignition source but given the relatively low flow rates from a drum it shouldn't build quickly as at least some of it will dissipate when the fuel makes contact with the funnel.

 

Not using the funnel would make the fuel charging issue less as a spark inside the tank would be much less dangerous than one inside the tank. This is because the fuel air mixture is too rich (unless the tank is empty) to cause ignition.

 

Those who don't use a funnel will probably have less risk of fire but greater risk of fuel contaminants being an issue. I know of some people who never use one and routinely fill up with mogas. I wouldn't ever dispense with a funnel personally.

 

 

[nomadpete]

Just to add to this very valid discussion...

 

I have heard of two instances of fuel ignitiion whilst refuelling - as retold by witnesses. These were whilst refilling boat tanks but that really doesn't matter. The common factors were:

 

1. low humidity.

 

2. both persons were wearing their spray jackets.

 

In each case the ignition happened during the fuelling, not at the moment of putting nozzle to tank.

 

At the time the blame was put on the static from synthetic spray jackets. This suggests that ignition was caused by something that occurred after the nozzle contacted the tank. So the usual suspects were already at the same potential.

 

It is all very well to provide a leakage path between airframe - ground - jerrycan - body. But it is equally important to avoid creating static on your insulating garments.

 

I like the idea of wiping a plastic tank with a damp rag, while your other hand is in contact with the airframe.

 

Bluey, were you wearing a synthetic jacket?

 

 

[Bluey]

No, I was wearing a pair of shorts and a t shirt. The t shirt was cotton and polyester blend. I do recall the drum brushing up against my leg as I walked it the five metres or so to the trike. I then put it down, open the cap, installed the nozzle and started fuelling.

 

 

[Head in the clouds]

Just to add to this very valid discussion...I have heard of two instances of fuel ignitiion whilst refuelling - as retold by witnesses. These were whilst refilling boat tanks but that really doesn't matter......

 

In each case the ignition happened during the fuelling, not at the moment of putting nozzle to tank.......

 

.......Bluey, were you wearing a synthetic jacket?

Yes, fuel fires are not all that uncommon and so it's good to have a discussion and focus on some of the issues. Note in the video posted recently, the lady was wearing a sweater that was likely to have at least some acrylic content, and also that the fire was ignited during the refuelling, not at the first contact of the nozzle.

 

Since we're talking about fuel fires I'll just mention a different type of one that happened to me and caused months of frustration ultimately, and although I didn't get injured or burn the boat down if a couple of things had happened differently it could have been much worse.

 

I was having trouble with an outboard (as you do) and suspected fuel wasn't getting through due to a faulty fuel pump or perhaps a blocked fuel line or maybe the float valve was blocked or jammed. I took the float bowl off and planned to crank the engine and see if fuel came out the float valve. Since I had previously introduced some fuel into the engine via the carby throat and the cranking was by key start (therefore ignition would be on) I didn't want the engine to fire unexpectedly because if it turned out that there wasn't a fuel supply problem it would have sprayed fuel around due to the float bowl being removed. So I stupidly removed the spark plug caps but didn't ground them.

 

When I cranked the engine fuel was delivered via the float needle valve (so there wasn't a fuel delivery problem) and it promptly ignited due to a spark from the plug caps. There wasn't much of a fire because the fuel stopped when I stopped cranking but for months after that the engine would run fine for about half an hour and then start flooding and stop. To cut a long story short, the little fire had made a tiny hole in the bottom of each of the floats so after a while they filled up with fuel and sank, allowing the float needle valve to stay open and flood the engine. I didn't find the problem for ages due to shutting off the fuel and eventually getting the engine running again after each problem event, and running the engine out of fuel (as you do with outboards), so when I checked the float bowls the floats weren't full of fuel since it had run out when the engine was run out of fuel. Hence it's nice that Rotaxes have solid foam floats ...

 

 

[nomadpete]

So, Bluey, was the flash at the instant of putting the nozzle into the fuel tank opening? Or was it after the fuel started flowing?

 

 

[facthunter]

I recall one plane I flew that gave me a great belt as my foot contacted the ground when exiting. I've had it with cars too. I don't think the ground is as important as all the other elements in the equation. Pump, aircraft, container at the same potential. More important is cigarette smokers downwind of your fuelling operations, and people who do it IN Hangars. FOOLS. Nev.