Explosion: Forklifts 2

[macfa1]

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

 

[IFRs]

Can you put something on the tires, sort of like snow chains or ice studs?

 

[macfa1]

IFRs - the problem with snow chains and ice studs ist that they are made of steel and have the potential to create sparks!
But thanks for the tip anyways

Alan

 

[zdas04]

Have you talked to tire manufacutrers about the possibility of a rubber that was more resistant to oil absorbtion? Maybe a spray-on/dip-in polymer that could be applied periodically? Seems cheeper in the long run than machining the tires every 3-4 months and replacing them every year.

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

http://www.muleshoe-eng.com

 

[patdaly]

macfa1,
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.

 

[TheTick]

Drag a brass chain underneath the chassis.

 

[unclesyd]

TheTick has the right idea. They make a grounding strap that is used for gas delivery trucks.
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?

 

[bvi]

Why do you think a copper wire or chain could create sparks? I would think if you were always grounded you wouldn't build a potential difference to cause an electrical spark. And I thought, from a spark from impact point of view, the material was non-sparking (I can't tell you this with a great deal of assurance, but suggest it as something to check). From the point of view of the end of the wire or chain getting dirty, its easier to clean that than machine off a layer of tire. Make it a practice to periodically clean off the device.

 

[diamondjim]

Can you stretch an inner tube
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.

 

[hacksaw]

the chain does not eliminate static sparks it only limits the amount of energy buildup available for the spark.

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.

 

[ccw]

Hi macfa1,
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.

 

[pennpoint]

ccw
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

 

[macfa1]

Hi all,

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

 

[macfa1]

Just to clarify - we do not let flammable material build up.

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!

 

[zdas04]

macfa1,
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

http://www.muleshoe-eng.com

 

[corrosionman]

macfa1 ok, here is another idea. Rubber is made non static and conductive by addition of a heavy loading of carbon in the tyre formula.Some years ago I re-tyred my FLT by castin new urethane polymer rims on all four wheels. It gave me several years of extra life. Check to see if you can get your wheels done similarly but with a high conductive urethane. You might have to point the direction to the selected urethane moulder.
Alternatively use solid tyres that can be machined and re-cut many times before becoming too small. Cheers DW

 

[funnelguy]

What are the forks made out of?

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.

 

[chicopee]

Use chainsor wire made of berryllium copper which is material used for wrenches and hammers by gas company employees and insurance inspectors. Berryllium copper is non sparking and if it is ,it would produce a low energy spark.

 

[ornerynorsk]

You guys really know how to complicate a simple solution !!!

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!

 

[saxon]

macfa1, Instead of trying to put on a band-aid to fix a problem, eliminate the cause. Clean up the oil/chemical spills that are the cause of equipment ground loss. I'm a bit suprised that EHS & Management would allow such hazardous conditions to exist in the first place. Had any flash fires or unscheduled barbecues lately?

Hope this helps.
saxon