Area Classification of Analyzer Building utilizing Hygrogen gas

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I found a similar closed post from 2010 "Classification of Analyzer Bldg - Group B or Not?". I have a 24' x 12' building with forced ventilation (1 scfm/ft^2). There is an analyzer that uses pure hydrogen. The building is classified CL1 Div. 2 Group C and D. Similar to the referenced post, I am questioning whether or not the Group B rating is required. Responses to the referenced posts state there is no volumetric or rate criteria for a hydrogen leak that will affect the group classification. However, in NFPA 70 Article 625 Electric Vehicle Charging System, it is mentioned that batteries off-gas hydrogen during charging, but there is no mention of requiring these locations to be classified group B. This seems to imply that there is an acceptable level of hydrogen concentration before an area has to be classified Group B. What is this magical number? Where can this requirement be found? The problem is that this analyzer is being added to an existing installation that is only Class 1 Div.2 Group C and D rated. A classification of Group B would require a costly upgrade to the existing equipment. Any help is appreciated.
 

rbalex

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I found a similar closed post from 2010 "Classification of Analyzer Bldg - Group B or Not?". I have a 24' x 12' building with forced ventilation (1 scfm/ft^2). There is an analyzer that uses pure hydrogen. The building is classified CL1 Div. 2 Group C and D. Similar to the referenced post, I am questioning whether or not the Group B rating is required. Responses to the referenced posts state there is no volumetric or rate criteria for a hydrogen leak that will affect the group classification. However, in NFPA 70 Article 625 Electric Vehicle Charging System, it is mentioned that batteries off-gas hydrogen during charging, but there is no mention of requiring these locations to be classified group B. This seems to imply that there is an acceptable level of hydrogen concentration before an area has to be classified Group B. What is this magical number? Where can this requirement be found? The problem is that this analyzer is being added to an existing installation that is only Class 1 Div.2 Group C and D rated. A classification of Group B would require a costly upgrade to the existing equipment. Any help is appreciated.
I found the bold statement to be astounding because there isn't a similar statement in Article 480 and storage batteries are capable of generating far more hydrogen than a vehicle charging station. I had to go and reread Article 625 and found no such statement like it. Some battery types do off-gas hydrogen while charging but the rate is very low, less than 1%.

Hydrogen has a very broad flammability range (4 - 75%) which means a 1% concentration would be sufficient to classify the location Group B. I'm not a strong fan of gas detection and none of the applications listed in 500.7(K) are valid for your described installation anyway. Even if they were, a gas detector automatically makes the location Division 2 for the gas being detected; otherwise, there would be no need for a detector.
 

GoldDigger

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I found the bold statement to be astounding because there isn't a similar statement in Article 480 and storage batteries are capable of generating far more hydrogen than a vehicle charging station. I had to go and reread Article 625 and found no such statement like it. Some battery types do off-gas hydrogen while charging but the rate is very low, less than 1%.

Hydrogen has a very broad flammability range (4 - 75%) which means a 1% concentration would be sufficient to classify the location Group B. I'm not a strong fan of gas detection and none of the applications listed in 500.7(K) are valid for your described installation anyway. Even if they were, a gas detector automatically makes the location Division 2 for the gas being detected; otherwise, there would be no need for a detector.
I think you may be missing or minimizing two points:

1. It has been a very long time since vehicle batteries (other than forklifts, golf carts and the like, which are excluded in 625.2) have been lead acid. If any other battery type got into a condition where it vented hydrogen, the ignition source would already be there in the damaged battery. (See Boeing 787, for example.)

2. I think that the OP is referring to the use of a hydrogen leak detector, where you pump down a vacuum system into a mass spectrometer and squirt hydrogen at various parts to see where the leak is OR you pressurize the system under test with a hydrogen/inert gas mixture and sniff for the hydrogen coming out.
In both of these cases, there should be precautions in place to make sure that no explosive concentration of hydrogen will be created in normal operation.
However, just having the hydrogen tanks and regulators present may be enough to create a classified area.
Such a gas detector would NOT be of the type intended for a 500.7(K) purpose.

PS: I find the definition of a "non-vented storage battery" in 725 as one which has no provision for venting excess pressure either misguided or useless, since nobody would ever make such a battery.
 
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rbalex

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I think you may be missing or minimizing two points:

1. It has been a very long time since vehicle batteries (other than forklifts, golf carts and the like, which are excluded in 625.2) have been lead acid. If any other battery type got into a condition where it vented hydrogen, the ignition source would already be there in the damaged battery. (See Boeing 787, for example.)

2. I think that the OP is referring to the use of a hydrogen leak detector, where you pump down a vacuum system into a mass spectrometer and squirt hydrogen at various parts to see where the leak is OR you pressurize the system under test with a hydrogen/inert gas mixture and sniff for the hydrogen coming out.
In both of these cases, there should be precautions in place to make sure that no explosive concentration of hydrogen will be created in normal operation.
However, just having the hydrogen tanks and regulators present may be enough to create a classified area.
Such a gas detector would NOT be of the type intended for a 500.7(K) purpose.

PS: I find the definition of a "non-vented storage battery" in 725 as one which has no provision for venting excess pressure either misguided or useless, since nobody would ever make such a battery.
Yes - so? The OP analyzer building is still Group B as described.
 

GoldDigger

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Yes - so? The OP analyzer building is still Group B as described.
How about putting the analyzer into a separately partitioned area of the building to avoid having the whole building reclassified? Might be cheaper than replacing all the other equipment to the Group B standard, yes?
 
I think you may be missing or minimizing two points:

1. It has been a very long time since vehicle batteries (other than forklifts, golf carts and the like, which are excluded in 625.2) have been lead acid. If any other battery type got into a condition where it vented hydrogen, the ignition source would already be there in the damaged battery. (See Boeing 787, for example.)



PS: I find the definition of a "non-vented storage battery" in 725 as one which has no provision for venting excess pressure either misguided or useless, since nobody would ever make such a battery.

Boeing 787 issue was lithium batteries. No hydrogen emission, it is a runaway exothermic reaction, fire, not explosion.

"Non-vented storage batteries" are equipped with gas absorption material where the generated hydrogen is being reabsorbed and converted into electrolyte.
 

GoldDigger

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Boeing 787 issue was lithium batteries. No hydrogen emission, it is a runaway exothermic reaction, fire, not explosion.

"Non-vented storage batteries" are equipped with gas absorption material where the generated hydrogen is being reabsorbed and converted into electrolyte.

Yes, but they still require a mechanism for venting excess pressure, that is pressure of gas generation greater than the absorber and catalyst can handle.
 
Yes, but they still require a mechanism for venting excess pressure, that is pressure of gas generation greater than the absorber and catalyst can handle.

The absorber and catalyst are sized to handle NORMAL discharge rate. Venting is only provided to handle catastrophic discharge, eg. short circuit and the quantity of emitted hydrogen from a single cell - unless you claim that every cell in the entire banks shorts at the same time - is insignificant quantity.
 

GoldDigger

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The absorber and catalyst are sized to handle NORMAL discharge rate. Venting is only provided to handle catastrophic discharge, eg. short circuit and the quantity of emitted hydrogen from a single cell - unless you claim that every cell in the entire banks shorts at the same time - is insignificant quantity.

I am not arguing that it is significant, just that the definition in NEC is badly worded
 

GoldDigger

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Would you cite which 'definition' do you find objectionable in the NEC and why?

The definition of sealed battery, in that it states that there is no provision for venting excess pressure.
There is no provision for venting normal overpressure, but there is always a provision for venting excess (abnormal) pressure.
 
The definition of sealed battery, in that it states that there is no provision for venting excess pressure.
There is no provision for venting normal overpressure, but there is always a provision for venting excess (abnormal) pressure.

This what the NEC actually states:

(B) Sealed Cells. Sealed battery or cells shall be equipped
with a pressure-release vent to prevent excessive accumulation
of gas pressure, or the battery or cell shall be designed
to prevent scatter of cell parts in event of a cell
explosion.

It provides exactly what you're complaining about that it does not.
 

GoldDigger

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This what the NEC actually states:

(B) Sealed Cells. Sealed battery or cells shall be equipped
with a pressure-release vent to prevent excessive accumulation
of gas pressure, or the battery or cell shall be designed
to prevent scatter of cell parts in event of a cell
explosion.


It provides exactly what you're complaining about that it does not.

Your quote comes from 480.10 (2011), which goes along with the definition in 480.2:
Sealed Cell or Battery. A cell or battery that has no provision for the routine addition of water or electrolyte or for external measurement of electrolyte specific gravity and might contain pressure relief venting
.
(And to some engineers, a weak spot in the individual cell casing intended to "prevent scatter of cell parts in event of a cell
explosion" is considered a vent, while the new firebox around the Boeing 787 battery would fit the secondary definition. Note that it was designed to contain the fire (not explosion, Boeing insists that there was no explosion) surrounding a battery containing vented (weak spot) cells.)

FWIW, wording preferred by Lithium battery manufacturers:
catching fire ---> venting with flame
explosion ---> spontaneous rapid disassembly


I was looking ONLY at 625.2 (2011) which makes the following definition:

Electric Vehicle Nonvented Storage Battery. A hermetically sealed battery, comprised of one or more rechargeable electrochemical cells, that has no provision for the release of excessive gas pressure, or for the addition of water or electrolyte, or for external measurements of electrolyte specific gravity.

Independent of other statements about storage batteries of provisions about their design, this definition is semantically flawed. Perhaps CMP 12 could use a little technical guidance on battery design from CMP 13. (And yes, I do recognize that 480 deals only with stationary installations.)

Now I can see a possible need for a distinction between a Sealed battery and a Non-Vented battery, but in that case I do not know of any Electric Vehicle battery pack that actually uses Non-Vented batteries matching that definition. On that basis, I continue to assert that the 625.2 definition does not serve its intended purpose.
 
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