Explosion: Forklifts
Explosion: Forklifts
(OP)
Hi all,
very interesting problem here: We have forklifts on our site that have to Explosion Proof, I.e Earthed so that no spark occurs, which could potentially cause an explosion.
The forklifts are constantly driving over oil patches and after about 3-4 months, so much oil is soaked up by the tires that they are no longer deemed “Earthed”.
Because of this we have to machine off a layer off the tires in order for them to be “Earthed” and we can only do this a maximum of 2 times, because the tires would be too weak to take any more machining.
We have tried and tried to come up with ideas to keep the forklifts earthed. We can´t do anything about the oil, so we need to come up with a solution to keep the forklifts earthed.
One solution was to have a copper wire hanging from the back or front of the forklift (like a lot of cars use to have in the 80´s to “supposedly” stop the passengers from becoming travel sick). However, most people thought that the wire itself might cause sparks itself or that a clump of oil would build up at the end of the copper wire and would itself become unearthed.
Do any of you guys have any ingenious solutions.
Would be greatly appreciated.
Thanks in advance,
Alan
very interesting problem here: We have forklifts on our site that have to Explosion Proof, I.e Earthed so that no spark occurs, which could potentially cause an explosion.
The forklifts are constantly driving over oil patches and after about 3-4 months, so much oil is soaked up by the tires that they are no longer deemed “Earthed”.
Because of this we have to machine off a layer off the tires in order for them to be “Earthed” and we can only do this a maximum of 2 times, because the tires would be too weak to take any more machining.
We have tried and tried to come up with ideas to keep the forklifts earthed. We can´t do anything about the oil, so we need to come up with a solution to keep the forklifts earthed.
One solution was to have a copper wire hanging from the back or front of the forklift (like a lot of cars use to have in the 80´s to “supposedly” stop the passengers from becoming travel sick). However, most people thought that the wire itself might cause sparks itself or that a clump of oil would build up at the end of the copper wire and would itself become unearthed.
Do any of you guys have any ingenious solutions.
Would be greatly appreciated.
Thanks in advance,
Alan





RE: Explosion: Forklifts
RE: Explosion: Forklifts
But thanks for the tip anyways :)
Alan
RE: Explosion: Forklifts
You should be able to solve this with a materials answer instead of a mechinism answer. Maybe you could get brass snow chains or carbon-fiber ice studs?
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
RE: Explosion: Forklifts
I would look to a solution similar to that of the common carnival bumper car, only in reverse. Affix a spring loaded Bronze "shoe" to the rear of the forklift. The spring action will keep it in contact, and the shoe could have channels to allow oil, etc to pass thru, while keeping earthed. It would not have to be terribly large, and replacing Bronze shoes, even on a monthly basis would be far cheaper than your current procedure.
RE: Explosion: Forklifts
RE: Explosion: Forklifts
What type of trucks are these, electric or gas?
I can't see allowing a flammable material to accumulate to the extent that such a requirement is needed.
How do you eliminate sparks for the motors or controls?
RE: Explosion: Forklifts
RE: Explosion: Forklifts
around the od of the tires acting
as a throw away rim or can a
rubber rim be designed to go around
the perifery of the tire.
I assume the tires have to be infalated
and the rims could be designed to
go on before you inflate the tire.
RE: Explosion: Forklifts
you don't want the chain to spark on its on contact with the floor, either so non-sparking materials are good.
not quite sure what you mean be explosion proof: mine safe, the electrical code (US/Cenelec/etc). typically explosion proof is assigned to electrical equipment and requires that the electrical enclosure be able to contain ignition of flamable components that might accumulate there.
RE: Explosion: Forklifts
After reading your post, I close my eyes and imagine a company named "Dyna-Energy" with fork trucks hauling barrels of diesel oil to the fertilizer mixing vat, or tolulene to the TNT vat or glycerin to the nitro vat! Interesting indeed.
You did not mention the floor. Is it metal, wood, concrete?
If the imagined scenario was correct, I would have the "explosion proof" trucks tethered more dependably to an overhead ground wire or bus bar, with multiple contacts on the slide shoe so (at least statistically) constant connection was maintained.
RE: Explosion: Forklifts
I do not know of any Dyna-Energy. But I cannot believe this scenario you describe, occuring in the USA! I just cannot.
macfa1 please! Where is this installation (general location Ok!).
In fact if its as oily as you (macfa1 say), then you should keep it that way and the more liquid the better. Keep everything submurged in the oil and keep the oil cool. I have put out many a lit match in a flammable liquid without it burning (just to illistrate this point). Its the mixture of air to vapour thats the problem. Blow the vapour away with high volume airflows.
Use fork lift trucks with oil submurged electrical components (e.i. dielectric oil). I can imagine these as dedicated fork lifts restricted to specific areas of use.
All of the above posts have good suggestions and all or most can be incorporated.
But! I am still having a problem with all that oil in the first place. What up with that?
Iwould not work there.
Please enlighten us all
pennpoint
RE: Explosion: Forklifts
the company is an international company (producing chemicals/polyethylene), and the site is based in Germany. German Regulations require any company working in Germany to comply to the most stringent of safety standards of any country in the Western world. I have worked in the US, England, France and Scotland, and compared to all Germany is a dream - never felt safer!
We have had a few meetings with "Continental", the tire manufacturer, and the tires that they have supplied with us are the best Ex-Proof tires they have available. We have tried other tire manufacturers, but none of them have the same standards as Continental! But even with all their expertize they can´t come up with an answer!
The ground is made of concrete, but the forklifts travel over metal doorframes, and can easily come in contact with metal equipment/objects, etc...
Forklifts can jolt, which is why a copper/brass/berylium strap at the back of the forklift could potentially be lifted off the ground long enough to cause a potential difference to be produced, thus causing the unwanted spark!
"unclesyd" - to answer your question - every single motor or electrical equipment on site is Ex-Proof...German Regulatons!
"pennpoint" - in the chemicals/oil industry it´s very difficult to keep the plants 100% clean - oil spillages do occur and it doesn´t take much oil/dirt to build up on the back of a metal strap. The oil the gets into the tires takes 3-4 months to get into the tires, because the forklifts travel in areas where there is a possibility of oil being present.
"hacksaw" - what I mean by explosion proof is that the equipment is protected from causing a Potential Difference from occuring - the Cell Phones we have on site are encased in rubber, thus not allowing any spark that might occur in the internal working to be exposed externally, thus eliminating the chance of a spark meeting an explosive gas/Liquid, which could cause us a few problems :)
Cleaning the tires on a weekly basis has also been tried, but that still does not work! Cleaning the strap can be done at the end of a shift, but that still doesn´t decrease the possibility of oil/dirt build up during a 12hr day! We´ve tried it!
By the way, the trucks are Gas powered, which is another reason why we don´t want a spark to occur, even though the gas should not be leaking out of the trucks, it´s better to be safe than sorry :)
the forklifts are used to carry anything and everything in the Polyethylene plants - of all 25 assets on site only the Polyethylene Plants are affected!
Hope this managed to clear a few points, but I myself am still looking for the answer!
Alan
RE: Explosion: Forklifts
The requirement for Ex-proof is so that if for some terible reason a pipe with Ethylene is leaking, that an explosion will not occur due to the forklifts producing a spark.
Prevention not cure is what we´re looking for...like I said stringent German regulations!
RE: Explosion: Forklifts
Did you consider diamondjim's suggestion above? Seems like a disposable inner tube designed to fit the tires tightly would be easier and cheeper than machining the tires.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
RE: Explosion: Forklifts
Alternatively use solid tyres that can be machined and re-cut many times before becoming too small. Cheers DW
RE: Explosion: Forklifts
I think a refinement of patdaly's idea would work. Use a spring loaded tensioner arrangement, but use a wheel instead of a sliding shoe for the contact point. This would alleviate your concerns about jolts lifting ground straps away from the ground.
I would look into using bronze brush wheels. These could be swapped out at specified intervals with the soiled units headed into a vapor degreaser or some such for cleaning.
If rolling brushes are still a concern, engineer the "fifth wheel" to accept a rubber compound optimized for the grounding service. At the very least you will get better life from your loaded tires.
I submit that if a brush wheel clogs and becomes ineffective, then a rubber wheel would be equally ineffective regardless of carbon black levels.
RE: Explosion: Forklifts
RE: Explosion: Forklifts
I think it was Tick and chicopee who suggested a bronze chain dragged beneath the chassis contacting the floor. This is how tanker trucks have been doing it for years. A simple solution that works!
RE: Explosion: Forklifts
Hope this helps.
saxon
RE: Explosion: Forklifts
saxon
RE: Explosion: Forklifts
RE: Explosion: Forklifts
But I do have control over the forklifts, and have responsibility to keep my men out of danger!
Bit dramatic with the BBQ - Just cleared 17million man-hours without a day away from work, which I think is pretty sweet, considering some of the things I've seen in my time, especially in the States - Houston to be exact :)
Thanks for the tip anyways!
RE: Explosion: Forklifts
However if there is objection to sliding contact or dragging things about, how about rolling contact on the existing wheels?
Think about this:
A conductive band (e.g. a metal band 1" wide by 1" thick) with an O.D. slightly (say 0.5" to 1") larger than the existing rubber wheels. The band is attached to the existing wheel hub (metal) using say six soft coil springs.The band would be located parallel to and either inboard or outboard of one or more of the existing rubber wheels, with a small gap between band and wheel face. When the vehicle is resting on the ground the band centre will higher than the wheel centre by half the diameter difference. The coil spring compression should ensure reasonable contact with the ground, but by using soft springs, grip of the rubber tyres will not be sacrificed. The conduction path would be from the existing hub, through the spring (or parallel connecting braids if thought necessary), through the band and into the floor.
There are about a million improvements that could be suggested (e.g. driving dogs guide plates, rubber instead of springs, number of wheels needing this etc), but you are looking for an idea, so hopefully its well enough described for you to get the picture.
Will it work any better? I doubt it, but it could be made to look good, which should keep the boys happy.
Let me know if you understand the description.
Cheers
Steve
RE: Explosion: Forklifts
RE: Explosion: Forklifts
RE: Explosion: Forklifts
Now, while we are at our computers, discussing safety, designing safe processes, etc., what are the guys in the warehouse doing with the forklifts?
For a glance, go to www.cargolaw.com, and in the right hand column, under "important features," find "singles only". Click there, and scroll down under the yellow header, and find in "2003, the first half" a feature titled "Safety lift June 2003"
My comment, we as engineering professionals can design all the safety into the process that we want to, but if the idiots in the warehouse are going to committ unsafe acts, we can never win.
By the way, while you are at the site, look at the photo immediately above the one I sent you to, entitled "F-22 Stealth Fighter Bomber." Enjoy!!!
rmw
RE: Explosion: Forklifts
If you are a Power Oriented engineer, by all means see "no right turn-Oct 2002" also under "important features" in the right hand column, except click on "photo Gallery of transport loss" and look down past the yellow background area to the white background part.
We as engineers cannot design around some of the blunders that are to be found on this site, no matter how hard we try, but that does not mean we should quit trying.
rmw