Grounding a tank truck for unloading flammable liquids

I liked the post, thanks for sharing, honest and informative, could not be better!!! I will give you a positive post when I have finished writing this!!

Hi Andy,

Thank you, I really appreciate that! I was wondering if I would ever get a "Good Answer" - I tend to be more on the terse side when explaining things, something I am working on. I read much more than I write and have enjoyed reading your replies to posts on this forum.

May you have a blessed New Year!

Mike

You earned it!

It was not "Terse" it was good!!! I hope to see more of your posts!!

Have a great 2008 too!

Great story. Any turbulent liquid has electrons being jostled around. If the turbulent liquid is moving in a pipe. static charges can and will gather. That is why NFPA and OSHA have specific requirements for grounding and bonding during fuel transfer so that the static charges can be safely dissipated before a spark can be created. I'm glad you shared your story.

One of the benefits of this blog it to learn fron other's experience.

So thanks.

The process of sandblasting can sometimes be ''jolty''.

I disagree on some points. The velocity can be up to 5 meters/sec. Agian, you are not grounding anything in the transfer, you are bonding to the vwssels.

I do like the part about the bonding point being away from the connection. That single item is what cause all the fires that was thought to have been caused by cell phones while fueling cars. The act of removing the nozzle by a charged up person cause the person to discharge while bonding at the nozzel and/or breaking the bond before the charged was equalized.

I disagree on several counts to your comments:-

1) it has never been proved that a person using a cell phone can cause a spark. Attempts to set fire to flammable liquids and involving a mobile have never caused a problem.....or a fire!

Theoretically though, it is just about possible and I would not recommend anyone to try it just in case, but the voltages in a mobile are relatively low and the currents are relatively small......nylon and man made fabrics cause much higher voltages to be generated than any mobile if rubbed the right (wrong!!) way....especially in a dry atmosphere....100,000 volts are easy, with a visible spark when grounded....

2) The bonding should always be away from the flammable vapors (liquids do not burn, only the gases they give off!!) and should be made BEFORE any gases are around to be ignited. The bond should only be broken ONCE the liquids and their gases have been resealed. The bonding should be made to previously selected/tested bonding points....

Remember to keep pipe velocities at or below 1m/s to reduce the propspect of flammable liquids becoming electrostatically charged.

Hi PW,

I agree that the higher the velocity, the faster a charge can build up. What I would like to know is how the 1m/s value was determined as a limit for more safe transfer. Could you elucidate? I'm curious.

Best Regards,

Mike

Thanks for your comments.

Mikerho, You suggested you would look for the potential difference between truck and plant. In some of these cases the receiving vessel is FRP or a non conductive tank. The plant equipment is grounded with perminant hardware that is inspected and maintained.

It is the connection to a tank truck or a plastic tote container that we ground while unloading. If the clamp connection not made than wouldn't your suggestion give a false positive in that there is no difference in potential?

I am trying to understand how to confirm a "ground" or connection to the plant equipment is made and if it can be confirmed with only one clamp attached.

Paddler,

I have read your post and am thinking about how to reply. I have been quite busy - long hours at work lately and so have not had much spare time. I just wanted to let you know I am intending to respond, but it will probably be sometime this weekend.

Mike

Paddler,

There are two principles at work: Bonding and Grounding...

Bonding & grounding can be defined as providing an electrically conductive pathway between a dispensing container, a receiving container, and an earth ground.

This pathway eliminates the buildup of static electricity and allows it to safely dissipate into the ground. The Federal OSHA Regulations, 29 CFR 1910.106(e)(6)(ii) states:

"Class I liquids shall not be run/dispensed into containers unless the nozzle and container are electrically interconnected. Where the metallic floorplate on which the container stands while filling is electrically connected to the stem or where the fill stem is bonded to the container during filling operations by means of a bond wire, the provisions of this section shall be deemed to have been complied with."

All containers of Class I liquids (liquids with a flash point lower than 100 degrees Fahrenheit) need to be bonded and grounded during dispensing. This includes non-metallic containers, even though the construction material may not be recognized as conductive (for example, polyethylene). If the containers are not properly bonded and grounded, the resulting static spark could be capable of raising the vapor temperature above the flash point, causing an explosion.

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Perhaps you are dealing with an intermittant ground connection, and the clamp you refer to is actually for Bonding the dispensing container with the receiving one (as opposed to "grounding" them), and the indicator light you refer to actually illuminates only when a ground condition is present?

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Just my $0.02...

Hi JMAN,

the resulting static spark could be capable of raising the vapor temperature above the flash point, causing an explosion.

Many Class 1 liquids have flash points below zero. I feel that one of the main reasons we do not have more fatalities /injuries when handling/mishandling highly flammable, flammable and combustible fluids is the vapour/air ratios of these vapours, e.g. LEL & UEL.

Great care need to taken when handling ALL flammable liquids and gases.

Class I liquids (liquids with a flash point lower than 100 degrees Fahrenheit) need to be bonded and grounded during dispensing.

Even transferring diesel fuel (flash point min 61,5⁰C usually up around 90⁰C) all components must be bonded and earthed, failure to do this has resulted in explosions and/or fires

You have my cursiosity up. If I understand this correctly bonding is the connection between the giving and receiving vessel and grounding would be adding a ground(earth) connection as well.

Is it good or bad practice to have a bonding strap that gives you a ground as well or is it proper to have each vessel individually grounded?

I'm an ME not an EE but this is good knowledge to understand.

I have a question/comment regarding this topic I'd like to throw out there for some feedback. I've heard from a variety of sources in the safety field that "static electricity" is a surface phenomena, leading to a position that there's some merit and value to bonding and grounding a container even though it may not be conductive. I've sat in the middle of some rather heated arguments over this and am interested in some additional input/views.

I'd agree. When filling a plastic gas can, you should have it on the ground so that the electrons running on the surface of the container will go to ground and the nozzel should touch the container.

This

can cause this

One would hope that your plastic gas can is just that.........and not just a plastic can..............like some people use.

Non conductive plastics can generate the highest voltages. Anti static bags have been treated to allow voltages to dissipate quickly.

They also run down batteries on printed circuit boards with soldered in batteries!!!A lot of people forget that such boards need jumpers to remove the battery supply from the board itself when being protected inside an anti static bag!!!!

I design so that the light indicates continuity using "intrinsically safe" components. The voltage and current is limited. I also use the continuity to actuate a N.O. relay in the pumps motor control circuit. No continuity, no start.

Excellent!!

I had an operator receive a nasty shock from a silo which was being filled from a road tanker. Although there was an earth clamp between tanker and silo,the silo was on insulated loadcells. The earth straps across the cells had rotted away,so the whole setup,tanker and silo was doing a Van de Graff. The original installation was not formally earthed as there was no 'electrical' equipment installed on the silo.

It is necessary to ensure that any fixed plant is 'grounded' i.e. connected to earth with a nice thick strip to prevent any significant plant-earth potential building up,as well as a path for lightning. (Our silo stuck up like a 60ft rocket at launch).And that 'mobile' ,'visiting' or temporary plant is bonded.

Not to stretch the thread too far I hope,I have had to provide 'earth' bonds to big vacuum cleaners,air blow cleaning nozzles,shot blasters etc,as even blowing powder off plant can generate a hell of a kick,it may not be in itself lethal,but the shock can cause slips,trips and falls. An unearthed blowdown nozzle was used to blow dust out of a battery compartment,open lid,blow off dust,BOOM,top blown off batteries, operator sprayed with acid.

It is important that you find out exactly what the indicator light does and how it does it to satisfy yourself that it accurately shows the complete system integrity.

Don't rely on indicator lights proving proper and complete bonding and ground connections,but first make sure everything in the earth path is visibly solid,the indicators may then help maintain the system.

You make good sense, I will rate this as good and on topic.

I believe the clamp indicator light is lit when when your tank is effectively grounded. I am thinking that one side of a low voltage power source is connected to the unloading rack and the other side to the clamp. If the tanker is grounded to the rack, when the clamp is connected, the electrical path will be completed and the light will light. If there is a high resistance connection or no connection the light will not light. You are correct in assuming this to be a continuity tester.