Fuel safety

[cpicton1]

I can't figure out why people have to be shown or proved to them how or why something will kill or maim them. Common since should kick in somewhere along the process. It's like someone walking out on thin ice. They know it's not safe, they may fall threw and drown, but hey, lets try it anyway.

 

[Anonymous Poster]

Flashlight element, I agree. That would do it. A spark from (2-3) triple A batteries in series, maybe, if you held the thing really close to the filler neck and tried a couple of times...

A cell-phone actually igniting gas is far-fetched . The radiation is so low that it barely penetrates the skull ( which is another debate topic entirely.....). The radiation from the cell-tower maybe a few blocks away or the truck driving by keying the CB would be many times the energy from the phone.

By the way, my truck bed liner is great at supporting static charge build-up. My gas station actually has signs up warning about filling cans in the bed because of this.

Lawyers have much too much to do with safety signs, instruction manuals and general mayhem. IMHO.

 

[rdbrumfield]

I'm with you on common sense. When fueling my plane I always ground it before touching it with the fuel nozzle. In
Viet Nam we were shutting the doors on the engine and transmision and I had climbed down off the left pylon on a cobra and a rocket left the outboard tube. It felt like the whole thing blew up. nothing was on, and noone was in the cockpit. We had to figure it was caused by static, it only takes a volt and a quarter to launch one. It did however teach me not to stand in front of a loaded weapon, is gas any different, I think not.

 

[Anonymous Poster]

Agreed. Common sense combined with knowledge of what is dangerous is what will keep us alive and well.

 

[Phred]

Well guys I did not mean to make you mad.

As an Electrical Engineer I have a pretty solid understanding of cell phone internals. Thats why I have a hard time visulaizing how this can be a major hazard.
The flashlight I can see since the element itself becomes very hot and could easily ignite vapour. The inside of your phone does not reach high temperatures.

The danger of static and any other high voltage source is well documented. As is a high temperature source, like pouring fuel into a mower that has been running and is still hot. The basic physics that starts fires in these cases is well known.

Yes it is better to be safe than sorry but worying about problems that are on the order of probability similar to winning the lottery doesn't make sense either.

I was just wondering if any real study / scientifc analysis has been done on the cell phone issue.

Fred

 

[cpicton1]

Phred,

Nobody mad here. /w3tcompact/icons/grin.gif

I just have trouble believing how hard it is to make some people understand how easy it is to do something in a safe manner. We have safety meetings at work about once a month. Our safety director shows films, shows charts and we discus the way things should be done safely to prevent injury to ourselves and others. Five minutes after the meeting is over you will see a person that was just in the meeting with you doing what we just decided was unsafe to do, duh. I have done things myself and later wondered why I did it that way when a safer way was available. Oh well, some of us try to learn from our mistakes, if we live through them. /w3tcompact/icons/smile.gif

 

[herbenus]

Here's a link to a site which dispels many of the email hoaxes that are going around, one being the cell phone at gas pump. (It's amazing how many of these hoaxes I've been emailed.) Interesting site.

http://hoaxinfo.com/fear_health.htm

 

[TWINKLE_TOES]

Fred,

You don't need a lot of potential to cause an arc sufficient to ignite explosive vapors. Every time you open a contact carrying current an arc is formed, some so minute they may not be perceptable, but still there. Mechanical switches depend on arc dynamics for operation. As an example take a D cell battery and short momentarily across it. At the moment you remove the short a an arc is clearly visible. Whether this arc can transfer enough energy to the vapor for ignition is a whole diffferent problem. AAA batteries will also produce visible arcs, but substantially smaller. In the instant in time when the cell phone is turned on or off with mechanical contacts which bounce, the energy storage devices in the phone (capacitors) will draw high currents sufficient to generate similar arcs to the short circuit case. If you like good puzzles, monitor this arc voltage with a high bandwidth oscilloscope and explain why the amplitude is about twice the battery voltage. Patrick J. McCleer published a book while working for Mechancial Products titled "The theory and practice of circuit protection" Contact them and they will give you a complementary copy. It's a great book for your library.

 

[Phred]

Al,

Agreed switch bounce in mechanical siwtches is an issue but what if the swicthing is done with FETs?

In most phones you have no mechnical relays becasue they are large and bulky and you can do the job better with a microsopic silicon solid state switch. Now it does use membrance switches and in principle one could get an arc from that but the arc would be very small and the probability of igniting gas fumes while standing at the pump would approach zero IMHO. Keep in mind that these switches are typically in a matrix (like your key pad) covered by a silicon rubber sheet.

People are trying to tell us that just standing by the pump with a cellphone on your belt is a major safety hazard on par with pouring gas into a hot mower or static electricity.

I would worry far more about the electric fan in the newer cars that works off a temperature sensor and comes on even when the key is off.


Fred

 

[TWINKLE_TOES]

Fred,

Certainly the mechanisms for soild state switching do not rely on arcs for termination of the current. Also inherent in some mechanical switch designs explosion proof is embedded. The science of vapor ignition is well beyond my understanding. As a kid I demonstrated my brillance and bravery by extinguishing a kitchen match in diesel./w3tcompact/icons/frown.gif Perhaps the complexity of the problem breeds the conservatism that we see. Design requirements for killing people in the commercial world, have a probability of occurance for catastrophic events of 10E-9. Thats more cell phones than exists in the world. I would certainly call my wife on the cell phone to mow the lawn before I would fill a hot mower with gas.