Hazardous Area Classification

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mull982

Senior Member
We have a Coal Mill that we are trying to determine the Hazardous Classification in order to specify all the correct equipment. The design engineer had origonally listed on the design drawings that this area was a Class II DIV I area. The contractor has questioned this classification in regards to many of the equipment enclosures that were specified for the job which do not match this classification. There is now a heated discussion about what the actual classification is.

The main question seems to be who is ultimately responsible for determining the classification of a particular area. Is it the design engineer? Is it the client? Some people here are stating that it is the clients insurance company that dictates this classification?

If this area is indeed a ClassII DIV I area do all the enclosures in this area need to be rated for NEMA 7,8, or 9? Does this include receptacle enclosures? Doe the receptacles have to be GFI protected?
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Coal Mill is too generic of a term to categorize an area by. IS there a hazardous area clasification drawing? If, not that is the first step toward determining what is what.

There is no single entity that makes the determination. It is a combined effort between the standards, Owner, his insurer. Coal dust should be considered conductive. Enclosed areas where it can accumulate should be Class II, Div 1. Enclosed areas cut-off from dust are not classified, however you may want posivitve presure to eep the dust out.

Around Dust-tight fuel systems is not classified. The enclosed area above coal in silos is Class I, Div 1 as well as Class II, Div 1.

Some areas can be ventilated to keep gases from accumulating.

There are other areas to consider as well.

Like I said, it's not an easy determination without a lot mor detail.
 

mull982

Senior Member
Coal Mill is too generic of a term to categorize an area by. IS there a hazardous area clasification drawing? If, not that is the first step toward determining what is what.

There is no single entity that makes the determination. It is a combined effort between the standards, Owner, his insurer. Coal dust should be considered conductive. Enclosed areas where it can accumulate should be Class II, Div 1. Enclosed areas cut-off from dust are not classified, however you may want posivitve presure to eep the dust out.

Around Dust-tight fuel systems is not classified. The enclosed area above coal in silos is Class I, Div 1 as well as Class II, Div 1.

Some areas can be ventilated to keep gases from accumulating.

There are other areas to consider as well.

Like I said, it's not an easy determination without a lot mor detail.

There is a drawing that shows this area as being a Class II DIV II area, but others here are challenging it so I'm trying to get to a better understanding.

Basically there is a coal transprport conveyor which dumps coal into two large bins. From these bins there is another feeder conveyor that feeds the coal into a larger grinder mill. From the grinder mill the fine coal is stored in another large tank. From this tank the coal is pumped to other areas of the plant. All of the itmes that I just listed are located on an outdoor structure.

I'm trying to determine what type of enclosures, receptacles, etc.. are required with all of this equipment. Does is all need to be NEMA 7,8,9 for a class II Div II

Also all conduit fittings leaving and enering boxes are all standard gasketed fittings. Do these fittings need an extra layer of protection?
 

MJJBEE

Member
There is a drawing that shows this area as being a Class II DIV II area, but others here are challenging it so I'm trying to get to a better understanding.

Basically there is a coal transprport conveyor which dumps coal into two large bins. From these bins there is another feeder conveyor that feeds the coal into a larger grinder mill. From the grinder mill the fine coal is stored in another large tank. From this tank the coal is pumped to other areas of the plant. All of the itmes that I just listed are located on an outdoor structure.

I'm trying to determine what type of enclosures, receptacles, etc.. are required with all of this equipment. Does is all need to be NEMA 7,8,9 for a class II Div II

Also all conduit fittings leaving and enering boxes are all standard gasketed fittings. Do these fittings need an extra layer of protection?


Having Just gone through this as an owner. There are 2 answers the first is that you need to go back to the definition of class 2 div 1 vs div 2. The question you have to ask is during normal operations is there a sufficient mixture of coal and air to ignite? if that is the case then it is a Class 2 Div 1 area. If this is not the case then it is Class 2 division 2. there is a major cost difference between the areas. In a Class 2 Div 1 area there are many different choices that will meet the requirements in general most items will have to be dust ignition proof or pressurized. Look at section 502 of the NEC for all the requirements for class 2 locations.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am not an expert on coal dust but it would not surprise me one bit if there were parts of the whole area that could be properly classified one way, other parts classified another way, and parts some unclassified.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
We have a Coal Mill that we are trying to determine the Hazardous Classification in order to specify all the correct equipment. The design engineer had origonally listed on the design drawings that this area was a Class II DIV I area. The contractor has questioned this classification in regards to many of the equipment enclosures that were specified for the job which do not match this classification. There is now a heated discussion about what the actual classification is.

The main question seems to be who is ultimately responsible for determining the classification of a particular area. Is it the design engineer? Is it the client? Some people here are stating that it is the clients insurance company that dictates this classification?

If this area is indeed a ClassII DIV I area do all the enclosures in this area need to be rated for NEMA 7,8, or 9? Does this include receptacle enclosures? Doe the receptacles have to be GFI protected?
I have commented several times before that, outside Arts 511-516, there is no adequate way to determine electrical area classification from the text of the NEC. Since Arts 511-516 don?t generally apply to coal operations, we have a problem - especially since Section 500.4(A) requires proper documentation. Most folks would agree that ?proper? documentation requires it to be done by someone who knows what they are doing.

Section 500.4(B) FPN No. 2: references NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas - and that is where to start.

NFPA 499, Section 5.7 goes through the procedure of classifying a Class II facility/operation ?properly.?

Responsibilities? The Owner/Operator of a facility is always responsible to have classification done properly. Who actually does it can be anyone that actually knows what they are doing. I usually suggest someone that incurs risk, such as the facility insurance company or a design professional that understands the facility operation. Truthfully, most AHJs and their agents are clueless with regard to classification, although most are just fine when it comes to inspecting a proper installation.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
There is a drawing that shows this area as being a Class II DIV II area, but others here are challenging it so I'm trying to get to a better understanding.

Basically there is a coal transprport conveyor which dumps coal into two large bins.
Outdoor areas of coal handling system should not be classified as hazardous; however the inside of closed conveyors that are located outdoors should be Class II, Div. 1

Because of possible accumulation of methane gas, the confined space above the coal inside the covered storage silos (bins) should be classified as Class I, Div 1.

From these bins there is another feeder conveyor that feeds the coal into a larger grinder mill.
Methane gas in areas around conveyors or above the covered silos (bins) will not be sufficient to form hazardous concentrations and these areas should be only coal dust hazard, i.e. Class II. Div 1.

From the grinder mill the fine coal is stored in another large tank.

From this tank the coal is pumped to other areas of the plant. All of the itmes that I just listed are located on an outdoor structure.
Areas around dust tight pulverized fuels systems should not need to be classified.

I'm trying to determine what type of enclosures, receptacles, etc.. are required with all of this equipment. Does is all need to be NEMA 7,8,9 for a class II Div II

Also all conduit fittings leaving and enering boxes are all standard gasketed fittings. Do these fittings need an extra layer of protection?

The equipment in the classified areas needs to be rated for whatever classification is determined, in accordance with NEC.

I believe Factory Mutual provides good info, also check National Electric Safety Code (NESC).

Hope that provides some assistance.
 

mull982

Senior Member
We were finally able to confirm that the area in question is a Class II Div II Group F area.

Are the receptalces for this area required only to be dustproof (Nema 4X) or do they need to have some sort of arc suppression/mitigating device?
 

mull982

Senior Member
We were finally able to confirm that the area in question is a Class II Div II Group F area.

Are the receptalces for this area required only to be dustproof (Nema 4X) or do they need to have some sort of arc suppression/mitigating device?

Went back and re-read the code and the way I understand it is that the receptacle requires either a switch to prevent exposre of live parts, or a arc chamber for containing an arc but not both.

In other words if the receptacle has a switch that only allows energization when the plug is secure in the recptacle then no arc arc chamber is required. However, if the receptcale does not have a safety swtich, then an arc chamber around the plug is required. Is this correct?
 

rbalex

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Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Went back and re-read the code and the way I understand it is that the receptacle requires either a switch to prevent exposre of live parts, or a arc chamber for containing an arc but not both.

In other words if the receptacle has a switch that only allows energization when the plug is secure in the recptacle then no arc arc chamber is required. However, if the receptcale does not have a safety swtich, then an arc chamber around the plug is required. Is this correct?
I'm not sure what Section you reread, but the specific text for receptacles in Class II, Divison 2 is:
502.145 Receptacles and Attachment Plugs.

(B) Class II, Division 2. In Class II, Division 2 locations, receptacles and attachment plugs shall be of the type that provides for connection to the equipment grounding conductor of the flexible cord and shall be designed so that connection to the supply circuit cannot be made or broken while live parts are exposed.
How would a switch alone guarantee "...that connection to the supply circuit cannot be made or broken while live parts are exposed." Typically, you will need a receptacle identified for Class II, Division 2.

In general, enclosures in Class II, Division 2 need to be "dusttight," not necessarily "dustproof" (technically, dust-ignitionproof), but neither apply to Type 4X alone. (See Table 110.20 and its FPN)
 
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jdsmith

Senior Member
Location
Ohio
"...that connection to the supply circuit cannot be made or broken while live parts are exposed." Typically, you will need a receptacle identified for Class II, Division 2...

One example of a recpetacle that meets this requirement is the Crouse Hinds FSQC230. We use this receptacle for 120V, 20A outlets throughout the refinery - it is identified for Class 1 & 2, Div 1 & 2. When a user inserts the plug into the receptacle, they must turn it 90 degrees to activate the switch to turn the power on. When the plug is turned and the power is on the plug cannot be removed. To remove the plug, it must be rotated back 90 degrees to de-energize the receptacle before the plug is removed.

The receptacle is approximately $450, if you choose to install a fixed GFCI as we do the GFCI with a box is another $300.
 

mull982

Senior Member
I'm not sure what Section you reread, but the specific text for receptacles in Class II, Divison 2 is:How would a switch alone guarantee "...that connection to the supply circuit cannot be made or broken while live parts are exposed." Typically, you will need a receptacle identified for Class II, Division 2.


The way I understand it is that you need a twist lock plug that when connected allows you to close the switch on the receptacle to allow power to the receptacle. With this method you do not need any arc chamber surrounding the plug is this correct?
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
The way I understand it is that you need a twist lock plug that when connected allows you to close the switch on the receptacle to allow power to the receptacle. With this method you do not need any arc chamber surrounding the plug is this correct?
That might work if the switch can't be operated if the plug isn't completely engaged; do you have a cut sheet for an example?

For a Class II, Division 2 location only, the example jdsmith gave may be a bit overkill; but, if a facility also has Division 1 and needs enough receptacles for both Division 1 and 2 applications, then a single "one-size-fits-all" device looks quite reasonable to me.
 

mull982

Senior Member
That might work if the switch can't be operated if the plug isn't completely engaged; do you have a cut sheet for an example?

For a Class II, Division 2 location only, the example jdsmith gave may be a bit overkill; but, if a facility also has Division 1 and needs enough receptacles for both Division 1 and 2 applications, then a single "one-size-fits-all" device looks quite reasonable to me.

Attached is a cut sheet for one I was planning on using.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
That would not be accepted locally unless you could document it's listing for the given location (Class 1 Div II, etc)
 

jdsmith

Senior Member
Location
Ohio
Attached is a cut sheet for one I was planning on using.

That would not be accepted locally unless you could document it's listing for the given location (Class 1 Div II, etc)

I agree, the receptacle must be tested and listed for use in the particular area classification. I'm not familiar with any other receptacles other than what I posted because our plant standardized on it - we probably have 600-800 of them. I know in general that Crouse Hinds, Appleton, and Killark make hazardous location interlocked receptacles like this, I'm sure there are others as well.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I forgot about this thread until jdsmith bumped it back into my line of sight.

Section 500.8(A) was reformatted in the 2008 NEC. The content didn?t change, but it was done to reemphasize that listing and labeling are not the exclusive means of determining ?Suitability? for classified locations. While in some cases, listing is specifically required, it is not a general requirement.

I am not acting as an ?owner?s engineer? [500.8(A)(3)]; however, if the unit referenced in mull982?s cut sheet works as I understand it, it is my opinion that it should be accepted in Class II, Division 2 ? documented local jurisdiction rules excepted. It appears the ?Twist-Lock? ? feature mechanically prevents opening/closing the integral switch unless the plug is fully engaged. If that is true, it meets both the letter and intent of Section 502.145 as cited above.

Specific listing for Class II, Division 2 is not a requirement of Section 502.145 nor any preceeding superior rule. The ?general rule? for classified locations is in Section 500.8(B)(1): ?Equipment shall be identified not only for the class of location but also for the explosive, combustible, or ignitable properties of the specific gas, vapor, dust, or fibers/flyings that will be present?? Identified is not synonymous with either listed or labeled. All three are defined terms in Article 100.
 

dicklaxt

Senior Member
I can only contribute to this discussion from the other side and that being the Design Engineering firm.They are not experts in all matters and correct 100% of the time but collectively between client,engineering,plant standards,construction forces and ultimately the final sign off or stamp of approval,a certified document becomes reality and is issued for construction.Now thats Utopia some might say but thats the intent,and all equipment residing within the limits of that drawing/document must be tested and approved for use in that areas atmosphere as well as known acceptable construction practices,use of materials & devices.

The evolution of a site plot plan(equipment locations) goes thru many changes before it is finalized and things do fall thru the cracks thats why so many eyes are on the look out.

Schedules are demanding of ones time, approval cycles,long term delivery items and associated support documents & materials all play a major role in the finished package,while efforts must run parallel which breed changes and errors.

The construction schedule is probably the major driving force and milestones and restraints must be accomplished so everyone is on the same page at the same time and resolutions to errors accomplished in a safe constructive way.

The infighting between disciplines,finger pointing and "I'll show you" attitudes will always be part of our makeup and society, but in the end we get the job done together.

Boy I sure got carried away on this one,but my wife holds my feet in the fire and won't let me talk,that's what causes me to seek outlets elswhere.:grin:

dick
 
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