Can coal dust causes arc-flash? 1

[shlim]

Hi, I hope this is the right place to post this question.

I have an arc-flash incident, with known presence of coal dust accumulation and high humidity environment in the electrical room.

From my current readings, I note that some coal type are conductive and some are not. I am looking for literature review with reference to the concentration of coal dust required to cause an arc-flash.

Would an arc-flash requires airborne coal dust/particle, or by way of surface tracking plus sufficient mositure content could easily lead to arc-flash?

 

[waross]

The major component of coal is carbon.
If your readings indicate "not conductive" I suspect an issue with a good contact with the dust under test.
The solution is exclusion of the dust rather than trying to predict the next flash-over.
A common solution is to pressurize the electrical room with a constant supply of clean filtered air at low pressure.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Coal dust can certainly cause shorts. If you're lucky you won't also end up with a secondary dust explosion.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

It's probably possible - coal build up falling across exposed live parts could possibly initiate an arc. Coal dust, as Keith mentions, can cause explosions and can require NEC classification as hazardous location.

 

[crshears]

Don't know if it's apropos, but electrostatic charges can build up if coal dust is being vacuumed up with rubber hoses; I know this from experience as I used to have to keep my body bonded to ground with one bare hand while doing this task so I wouldn't get continuously zapped.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[RRaghunath]

"The solution is exclusion of the dust rather than trying to predict the next flash-over." very appropriate.

Rompicherla Raghunath

 

[PA28]

I am not sure it is correct to seek information not directly relevant to topic. But i am inclined to request information on pressurizing the electrical room indicated by Waross's reply.

We are struggling with a contractor to setup one, the contractor is clueless and we also do not have any guidelines / standards.

Can Waross direct to some source of information?

 

[waross]

If the electrical contractor is clueless, look for a Heating Ventilating and Air Conditioning consultant or contractor.
This is a ventilation problem, not an electrical problem.
You need a source of clean air, a good filter system with a low flow alarm across the filter and a fan to move the air through the filter and into the room.
You need an alarm to warn you when the filter is getting clogged.
You don't gain much if you filter until the filter gets so dirty and plugged that it ruptures and dumps a large volume of dirt/dust into the electrical room.
Too much pressure in the room will cause problems with doors not closing or not being able to open.
The doors should have self closers. Possibly two doors forming an air lock.
Do not use too much pressure. Given the large area of the walls and ceiling in square inches, it doesn't take much pressure to do damage to the walls or ceiling.
See an HVAC guy for better information on the installation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[RRaghunath]

To add to content of Bill's (Waross) post,
you may need to include automatic shutdown of pressurisation fans, on detection of fire.

Rompicherla Raghunath

 

[shlim]

I have actually forgotten to check on this thread because I did not receive any email notification.

I agree that the best way would be the improvement of the HVAC system for the electrical room.

Thank you all for the inputs.

 

[cuky2000]

See below the following excerpt from various sources:
For LV and indoor in dry conditions, coal have minimum impact on flashover since the coal may be considered as insulator since the high resistivity.

For outdoor installation in HV substation environment in presence of moisture reduce significant the resistivity and could be cause of flashover as indicate in the enclosed excerpt.

 

[Strong]

A search from OP words "concentration of coal dust required to cause an arc-flash"

https://www.bing.com/search?q=conce...-57&sk=&cvid=D206392168A44021BA8FF143C5569588

The short answer is yes coal dust could could cause arc-flash!


Walt

 

[BlackJackJacques]

Conductivity is not the only requirement for a Class II explosion -- if the dust is combustible. Take sugar dust for instance and sugar dust processing explosions. Yes - carbon dust is clearly combustible.