Carbon Black Area Classification

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powerpete69

powerpete69

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Northeast, Ohio
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Professional Electrical Engineer
There is an existing factory line that just got moved and wired. Now they want to look at area classification (obviously, should have been looked at before )
They are saying carbon black in question does not have an ignition temperature, but that excessive carbon build up can cause electric panels to short (some carbon can conduct electricity)

There is likely going to be a complete engineering study done, but has anyone had an experience with carbon black? Usually we classify them because the dust or vapor is explosive....this is apparently a non explosive issue.

Any thoughts or experience would be appreciated.
 
powerpete69 said:
There is an existing factory line that just got moved and wired. Now they want to look at area classification (obviously, should have been looked at before )
They are saying carbon black in question does not have an ignition temperature, but that excessive carbon build up can cause electric panels to short (some carbon can conduct electricity)

There is likely going to be a complete engineering study done, but has anyone had an experience with carbon black? Usually we classify them because the dust or vapor is explosive....this is apparently a non explosive issue.

Any thoughts or experience would be appreciated.
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An engineer with relevant experience should analyze the situation, but I would venture the opinion that this is Class II Div 1; " ignitable concentrations of combustible dust can exist, under normal conditions". They are crazy if they are really claiming there is no ignition temperature for carbon black. If the carbon black ever gets suspended in the air, say, due to someone banging a pipe or duct covered in the dust and it finds an ignition source, you'll have a very fine deflagration. If you have the space, make an air cannon and shoot a load of flour across an open fire and see what happens. Please God, do it remotely.
 
gadfly56 said:
An engineer with relevant experience should analyze the situation, but I would venture the opinion that this is Class II Div 1; " ignitable concentrations of combustible dust can exist, under normal conditions". They are crazy if they are really claiming there is no ignition temperature for carbon black. If the carbon black ever gets suspended in the air, say, due to someone banging a pipe or duct covered in the dust and it finds an ignition source, you'll have a very fine deflagration. If you have the space, make an air cannon and shoot a load of flour across an open fire and see what happens. Please God, do it remotely.
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I hear what you are saying, but per NFPA 499, there has to be more than 8% trapped volatiles to be considered group F. But I can't be sure.
Whether the dust cloud is visible or not plays a factor. Is there dust collecting on the machines?....also another factor.

Most of the electric panels have positive pressure, multiple dust collectors.....etc. I haven't seen the room yet, but just wanted to get the discussion going. Multiple fume hoods throughout as well. Thanks for your reply.

I'm curious if anyone has heard of carbon black causing short circuits?
 
I have to confess it's been a long, (very long) time since I worked with carbon black; however, if it isn't Group F for lack of entrapped volatiles, it becomes Group G as long as it still forms a "dust". Otherwise, it should be treated as Class III depending on build-up. It is a judgment call for the classifier.
 
powerpete69 said:
...I'm curious if anyone has heard of carbon black causing short circuits?
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I wouldn't want to find out.

Ten or 15 years ago I was called in to fix a low-power radio transmitter located in a hotel elevator penthouse. One-hundred years of carbon dust from the brushes coated most surfaces. A module swap fixed it, and we suspected a carbon build-up caused the problem. I think I swept up a mound of dust, plunged the VOM probes in, and got a high but measurable resistance value. I would imagine a little humidity and some settling or pressure to pack the particles together would decrease the resistance (and I have a WWII-era aircraft motor generator with a carbon-pile voltage regulator which works on that principle). I was asked to maintain this transmitter going forward, and was diligent in keeping it clean. Thankfully, the site was relocated to a cleaner place a few blocks away.
 
powerpete69 said:
...
I'm curious if anyone has heard of carbon black causing short circuits?
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I should have added non-saturated carbon black, especially vitrified, is fairly nonconductive. However, if medium voltage systems are involved various levels of "treeing" may be exhibited.

EDIT ADD: It appears grich and I were responding at the same time.
 
rbalex said:
I should have added non-saturated carbon black, especially vitrified, is fairly nonconductive. However, if medium voltage systems are involved various levels of "treeing" may be exhibited.

EDIT ADD: It appears grich and I were responding at the same time.
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Just curious here. Not really adding to the discussion, but...

Would bone black be as combustible?
 
I have heard of a horror story about carbon black. The 480v(lotta amps) main gear "BLEW UP".

The cause of the blowout was attributed to original installer used to much NO-LOX on the incoming lugs... The NO_LOX ran down the wiring and was subseqentially covered in carbon black and then arced out...
 
rt66electric said:
I have heard of a horror story about carbon black. The 480v(lotta amps) main gear "BLEW UP".

The cause of the blowout was attributed to original installer used to much NO-LOX on the incoming lugs... The NO_LOX ran down the wiring and was subseqentially covered in carbon black and then arced out...
Click to expand...
Since it is anecdotal, I can't say much but 480V is a little low in my experience for actual carbon black tracking. IT usually takes something in excess of 2400V. I suspect if it did happen, it is because the No-LOX is itself conductive.
 
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