Equipment required to be C1D1 in location protected by Gas Detection

[Natfuelbilll]

Given a C1D1 building so classified due to inadequate ventialtion and where a gas detection is properly installed and maintained is there
1. any reason - or Code - requiring any type of installed equipment be rated sutable for C1D1?
2. or can everything be C1D2?
3. or is there a requirement when the gas detection system is not functioning that C1D2 equipemt be de-energized and only C1D1 be used?

 

[dicklaxt]

....... if it has the concentrations of gases making it C1D1 in normal operating conditions then everything must be rated such.....the gas detection system is just that,A WARNING OF A LEAK it doesn't change the classification.It may alert an operator to start a shutdown manually or it can happened automatically thru a DCS (Distributive Control System)

dick

 

[rbalex]

You?re definitely asking the right questions. You?re using Section 500.7(K) as a protection technique and describing 500.7(K)(1) as a specifically recognized application.

The NFPA Manual of Style prohibits the direct citation of external documents in the ?body? of a Standard; however the reference in FPN No. 2 to ANSI/API RP 500 [RP 500] indicates the intention of CMP14 for the specific technique design requirements. RP 500, Section 6.5, USE OF COMBUSTIBLE GAS DETECTION EQUIPMENT describes two of the three applications listed in 500.7(K) [(1) & (2)] But note the ?NOTE? that applies to Inadequate Ventilation in RP 500, Section 6.5.1:

If an area contains equipment that may release flammable gases or vapors within the area during normal operations, gas detectors are not a feasible alternative unless some degree of ventilation is provided since frequent alarms or equipment shutdowns, or both, are likely to occur.

Personally, I don?t generally like gas detectors as a protection technique (if you are detecting gas, the location must at least be Division 2 by definition); nevertheless, they are recognized in very limited applications and those described in RP 500 are acceptable in my opinion, when all the requirements are observed.

I would recommend reviewing RP 500. The specific answer to each of your questions is there, but it also answers some additional questions that you didn?t ask, but probably should have.

 

[Natfuelbilll]

I have carefully read API 6.5 and NEC 500.7(K).

If the installation goes beyond 40% levels is C1D2 equipment permitted to stay energized?

In C1D1 areas where C1D2 equipment is installed (as permitted using the protection method of 500.7(K)) does C1D2 equipment remain suitable during infrequent (but possible) gas concentrations > 40% LEL?

Or does the rule flip flop?

 

[rbalex]

I have carefully read API 6.5 and NEC 500.7(K).

If the installation goes beyond 40% levels is C1D2 equipment permitted to stay energized?

In C1D1 areas where C1D2 equipment is installed (as permitted using the protection method of 500.7(K)) does C1D2 equipment remain suitable during infrequent (but possible) gas concentrations > 40% LEL?

Or does the rule flip flop?

In fairness to its advocates, it’s difficult for me to answer your questions because, as I said, I don’t generally like this protection technique. The NEC is inadequate in its description of proper use. Since I have endorsed RP 500, I’ll do my best though.

Section 6.5.2e says. “…sensing a gas concentration of 40 percent LFL (maximum) or a gas detector system malfunction should both activate an alarm … and initiate automatic disconnection of power from all electrical devices in the area that are not suitable for Division 2.” This would imply that that Division 2 equipment could continue to operate. The next reasonable question, of course is “How long?” The only significant clue is in the Note, “In the case of sensing 40 percent LFL or a gas detection system malfunction, corrective action to reduce the gas concentration should be initiated immediately.” Obviously, it can’t be permitted to continue indefinitely, but there is no definitely specified time limit either.

My opinion? If the system hits 40% LEL, it will hit full LEL fairly quickly since a significant leak has most likely developed. That may not be an absolute certainty; it could be a detector malfunction – but it’s a good bet. So in absence of absolute certainty of a detector malfunction, personally, I’d recommend an orderly shut down for anything not suitable for Division 1.