Autoignition temperatures and T-codes for Luminaires

[JimmyMac]

1) NEC 2017 Art. 500.8(B)(1) states "...In addition, Class I equipment shall not have any exposed surface that operates at a temperature in excess of the autoignition temperature of the specific gas or vapor". Art. 500.8(D)(1) states "The temperature marking specified in TABLE 500.8(C) shall not exceed the autoignition temperature of the specific gas or vapor to be encountered". Art. 501.130(A) is related to Class I, Division 1 luminaire installations and does not mention anything about autoignition temperatures, surface temperatures, or T-codes. I would take this to mean that in Class I Div 1 areas, the luminaires' surface temperature must not exceed the autoignition temperature of the gas or vapor present and must contain a T-code whose temperature does not exceed the autoignition temperature (AIT) of the specific gas or vapor present (in addition to meeting CID1 area). True? If I have misinterpreted this , please help me to better understand.

2) NEC 2017 Art. 501.130(B)(1) is related to Class I, Division 2 installations and states "Where lamps are of a size or type that may, under normal operating conditions, reach surface temperatures exceeding 80 percent of the autoignition temperature (AIT) in degrees Celsius of the gas or vapor involved, luminaires shall comply with 501.130(A)(1) or shall be of a type that has been tested in order to determine the marked operating temperature or temperature class (T code)." It appears that maybe the requirements for a Class I Div 2 luminaire are more stringent than for a Class I Div.1 luminaire. Isn't the T-code a requirement anyway? Am I meeting code if I specify a luminaire for a Class I Div. 2 area that is rated Class I, Div. 2 and carries a T-code whose temperature is less than the autoignition temperature of the specific gas or vapor present? I want to make sure that i am not misinterpreting and that the T-Code must be equal to or less than 80% the AIT of the gas or vapor present.

Thanks for your help!

 

[rbalex]

Actually, the requirements for Class I, Division 1 luminaires are far more stringent; it's just easier to say the complete assembly must be identified for Division 1. See Section 501.130(A)(1). (BTW if you are going to properly specify, it is Sections rather than Articles you were citing.)

With regard to Division 2, you cited all around a significant Section. See Section 500.8(C)(6)(a). Note not all general purpose assemblies are required to have a T-Code. Were it not for luminaires notoriously being heat producers, they wouldn't need to be marked at all. Section 500.130(B)(1) simply addresses the requirements for what would othrwise possibly be an acceptable general purpose assembly. Not all luminaire assemblies need to be specifically marked for Division 2 - but they are required to have an appropriate "T-Code".

 

[nec_addicted]

Auto Ignition for Cl 1 Div 1 & 2

Auto Ignition for Cl 1 Div 1 & 2

UL Online Certification Directory may assist rule for a "complete assembly" listed and tested for your target luminaries. IFUX guide information

UL permits the reproduction of the material contained in the Online Certification Directory subject to the following conditions: 1. The Guide Information, Assemblies, Constructions, Designs, Systems, and/or Certifications (files) must be presented in their entirety and in a non-misleading manner, without any manipulation of the data (or drawings). 2. The statement "Reprinted from the Online Certifications Directory with permission from UL" must appear adjacent to the extracted material. In addition, the reprinted material must include a copyright notice in the following format: "© 2017 UL LL

Might find the UL Online Certification Directory

 

[JimmyMac]

Thanks for your replies. One thing I would like to confirm is that I am interpreting the requirements for a luminaire in the different hazardous areas correctly. Below is what I interpret. Would you be kind enough to either confirm both 1 and 2 below or set me straight?

1) In a Class I, Div 1 area, the luminaire complete assembly shall be rated Class I, Div 1 (per 501.130(A)(1)) AND have a T-code that does not exceed the AIT of the vapors present (per 500.8(B)(1)).

2) In a Class I, Div 2 area, if the luminaires' T-code is greater than 80% of the AIT of the vapors present, then the luminaire shall be rated Class I, Div 1 (per 501.130(B)(1)) OR be rated Class I, Div 2 and marked with the T-code (which shall not exceed the AIT of the vapors present per 500.8(B)(1)).

The mention of T-codes being 80% of the AIT are throwing me off. Ultimately, I want to ensure that if I install a luminaire rated for the areas' Class, Div, Group for which it is installed AND the T-code temperature does not exceed the AIT, then I meet the NEC.

 

[rbalex]

1) The correct term is identified not “rated”. It may seem petty but, when we are talking Code, it means something. It doesn’t necessarily mean listed or labeled, but it does mean that it is readily recognized as suitable by the AHJ. [Section 500.8(A)]

2) This is basically correct. The difference is simply that the temperature rating or T-code has been determined by actual test.

 

[JimmyMac]

Thank you Bob!

 

[csc_wyo]

API RP 2216

API RP 2216

Bob,
Are you familiar with APR RP 2216? Given the encyclopedia of knowledge and education that you are to us all, I'm sure you are. 2216 states that based on science to date, the surface temperatures must be several hundred degrees higher than that the minimum AIT to ignite flammable vapors. It also states that pre-flame ignition and cool-flame ignition may occur at temps lower than the listed AIT. But I've seen 2216 used to argue the T-code limitation by EPC's, Vendors, Operators, etc. to justify using products above the 80% rule as well as CID1 rulings. Can you shed some light on how and if 2216 should be applied when determining T-Codes used in hazardous environments?

Thanks as always,
Ryan

 

[rbalex]

Bob,
Are you familiar with APR RP 2216? Given the encyclopedia of knowledge and education that you are to us all, I'm sure you are. 2216 states that based on science to date, the surface temperatures must be several hundred degrees higher than that the minimum AIT to ignite flammable vapors. It also states that pre-flame ignition and cool-flame ignition may occur at temps lower than the listed AIT. But I've seen 2216 used to argue the T-code limitation by EPC's, Vendors, Operators, etc. to justify using products above the 80% rule as well as CID1 rulings. Can you shed some light on how and if 2216 should be applied when determining T-Codes used in hazardous environments?

Thanks as always,
Ryan

The truth is I'm more aware of it than familiar with it. I'm familiar with the studies it is based on though. It was issued by an API Tech Committee I wasn't involved with. It was issued by the API Safety and Fire Protection Subcommittee rather than the Subcommittee on Electrical Committee (SOEE) that I was a member. Its major application intent was for mechanical and process equipment. Neither UL, IEEE nor NFPA bought into the studies with respect to electrical applications - which is why the NEC doesn't recognize it. Although the SOEE was interested, they never Proposed any NEC applications.

The underlying concept is mentioned in NFPA 497:

3.1.11 Minimum Ignition Energy (MIE). The minimum energy
required from a capacitive spark discharge to ignite the
most easily ignitable mixture of a gas or vapor.

The idea is where there is sufficient air movement, it takes a considerably higher temperature than the AIT to transmit enough energy to ignite an ignitable atmosphere.

 

[nec_addicted]

Auto-Ignition Temps

Auto-Ignition Temps

Trusted in all facets the wisdom above and truth's revealed.

Explanation's and exceptions apply to luminaries as special considerations. Example: Luminaries in a C1D1 environment may also require a C2D1 consideration based on the dust collected on the fixture when continuation of maintenance requires inspection and even possibly additional complication may arise in flammable flying's when temperatures are concerned.