Gas Monitor In a Hazardous Location

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fifty60

fifty60

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If I have a gas monitoring system that detects a level of gas that is below the lower explosive limit, how does that affect my area classification?

For example, a location that would be Class I Div 2 without the gas monitoring system. With the gas monitoring system installed, and functioning correctly, there will never be enough gas present to cause an explosion. Would this still be considered Class I Div 2?
 
just how does monitoring the gas level keep it from ever getting to a point where it is hazardous. The fact that it is a division 2 area means that on occasion it will be hazardous. even if you detect the hazard how does that prevent the hazard?
 
My question is more Machine-centric. The gas monitor alarm would shut down the machine. For example, a machine with heaters is going into a class I div 2 room. The lower explosive limit is 4%. There is a gas monitor inside the equipment to remove power from the machine when it detects 2%. Would the machine still need to be constructed for Class I Div 2, or could it be considered non-incendive equipment?


I definitely see problems with the above argument. For example, I would need to guarantee the heaters cooled off to less than 80% of the AIT of the gas or vapor present. But, is there anyway to use gas monitoring to prevent a hazardous environment classification?

Heaters are a bad example Lets us a motor for an example. The gas monitor would remove power from the motor when it detected low levels of gas or vapor. Can the motor then use normal non-sealed internal overload protection?
 
500.7(K) describes methods for using a combustible detection system as a means of protection with a number of requirements. I have seen/used combustible gas detection as a means to shutdown equipment but have not seen it used as a means to declassify an area.
 
nhee2 said:
500.7(K) describes methods for using a combustible detection system as a means of protection with a number of requirements. I have seen/used combustible gas detection as a means to shutdown equipment but have not seen it used as a means to declassify an area.
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It only allows the use in 3 cases.

(1) Inadequate Ventilation. In a Class I, Division 1 location
that is so classified due to inadequate ventilation, electrical
equipment suitable for Class I, Division 2 locations
shall be permitted. Combustible gas detection equipment
shall be listed for Class I, Division 1, for the appropriate
material group, and for the detection of the specific gas or
vapor to be encountered.
(2) Interior of a Building. In a building located in, or with
an opening into, a Class I, Division 2 location where the interior
does not contain a source of flammable gas or vapor,
electrical equipment for unclassified locations shall be permitted.
Combustible gas detection equipment shall be listed for
Class I, Division 1 or Class I, Division 2, for the appropriate
material group, and for the detection of the specific gas or
vapor to be encountered.
(3) Interior of a Control Panel. In the interior of a control
panel containing instrumentation utilizing or measuring flammable
liquids, gases, or vapors, electrical equipment suitable
for Class I, Division 2 locations shall be permitted. Combustible
gas detection equipment shall be listed for Class I, Division
1, for the appropriate material group, and for the detection
of the specific gas or vapor to be encountered.
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I don't see how his application can be shoehorned into one of these cases. maybe case 2 or 3 but based on what the Op said, I am doubtful.
 
petersonra said:
It only allows the use in 3 cases.



I don't see how his application can be shoehorned into one of these cases. maybe case 2 or 3 but based on what the Op said, I am doubtful.
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I agree - I would be skeptical of reliance on a gas detector as a means of protection/declassification, at least for a typical methane detector that I have used. But there are a couple of scenarios where it is allowed - am not sure if maybe it is used or more common in other non-natural gas installations.
 
Combustible Gas Detection System. (CGDS) [Section 500.7(K)] is a protection technique, it does not alter the classification. In fact, if you will read Subparts (1), (2), or (3) carefully, they simply say the CGDS permits using different types of equipment and wiring methods than would otherwise be permitted. NOTE: Subparts (1), (2), or (3) are the only applications permitted for CGDS.

"For example, a location that would be Class I Div 2 without the gas monitoring system. With the gas monitoring system installed, and functioning correctly, there will never be enough gas present to cause an explosion", is a false premise. Once detected, there is no guarantee the gas/vapor will be limited to the detected level. In fact, depending on the source, the gas/vapor may reach explosive levels within seconds - no matter how sophisticated the CGDS response is.


 
In 507 (1) (sorry not exact) it reads "due to lack of ventilation". Couldn't every scenario where you have a Hazardous area fit into the description of "Lack of Ventilation"?

It seems to me that as far as the NEC goes, the best you can do with an appropriately rated gas monitor is use Class I Div 2 equipment in some instances that you would have had to use Class I Div 1 equipment without the gas monitor.
 
Simply using CGDS is tacit recognition the location is at least Class I, Division 2. Otherwise, why do you have detection if you don't believe the presence of gas/vapor is a reasonable possibility.

AGAIN - reread Section 500.7(K) and its Subsections carefully. They permit using CGDS in only very limited applications. For the specified limited applications, Subsections (1) and (3) permit using Division 2 installations in locations that would otherwise be Division 1; Subsection (2) permits using ordinary installations in locations that would otherwise be Division 2.

Couldn't every scenario where you have a Hazardous area fit into the description of "Lack of Ventilation"?
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NO. Ventilation alone may (but not necessarily) reduce some (but not all) Division 1 to Division 2. Again, ventilation may reduce the size of a Division 2 envelope, but rarely eliminates it.
 
"Simply using CGDS is tacit recognition the location is at least Class I, Division 2." Hypothetical situation here, but I am still trying to understand this. If a person purchases a machine and requests a gas monitor for a group B, C, or D gas (for example), would the machine manufacture have to build the entire machine according to the Class 1 Div 2 requirements? Who actually specifies that the machine needs to be suitable for class I div 2? This would have to be the customer right?
 
fifty60 said:
"Simply using CGDS is tacit recognition the location is at least Class I, Division 2." Hypothetical situation here, but I am still trying to understand this. If a person purchases a machine and requests a gas monitor for a group B, C, or D gas (for example), would the machine manufacture have to build the entire machine according to the Class 1 Div 2 requirements? Who actually specifies that the machine needs to be suitable for class I div 2? This would have to be the customer right?
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The end user would be the one to tell the manufacturer any special machine requirements, including building it for a classified area.

Just because the customer requests a gas monitor does not mean that it automatically becomes C1D2.
 
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