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Thread: Ventilation In Class I Div 2

  1. #11
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    Quote Originally Posted by rbalex View Post
    Just curious which Subsection of 500.7(K) [(K)(l), (K)(2), or (K)(3)] do you believe your design "... satisfies the intent of the NEC and RP-500 ...". Note those are the only acceptable NEC designs.
    I find it interesting that the NEC only addresses a few of the multitude of possible scenarios regarding combustible gas detection. I'll agree that technically, our scenario may not meet the requirements of 500.7(K), however our various customers, third party inspectors, state inspectors and engineers that we work with find our installations more than adequate. The capacity of the 1/8"-1/4" sample lines that enter our analyzer buildings is quite limited and I have full confidence that our design provides a safe and secure installation. As far as all the line voltage heat and arc producing equipment that really matters, our design is fully in compliance with 500.7(A).
    Last edited by GoldDigger; 08-23-17 at 11:22 AM. Reason: Fixed QUOTE tag

  2. #12
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    Quote Originally Posted by Jim1959 View Post
    "...we utilize LEL gas detection, in conjunction with a fail safe control system that will start the exhaust fan..."
    You're spot on with your entire post and I do very similar things. However, I've learned a critical lesson before with a simple assumption. If you're truly looking for a fail safe solution, sending a command to a fan starter isn't exactly positive confirmation that your fan is running. Snapped/worn drive belts, spun couplings, local disconnects left open, HOA's in the OFF position or AUTO not proven are many ways to defeat that philosophy. I'm sure there are other codes, regs, guidelines that also specify a similar requirement, but NFPA 820 is very clear on what is required for positive detection. The last version I have is 2008, but in section 7.5.1, it sates that, "All continuous ventilation systems shall be fitted with flow detection devices connected to alarm signalling systems to indicate ventilation system failure." The cheapest and easiest way I've found to meet this requirement (in all industries I've engineered, not just wastewater) is to install a load side CT and relay on traditional starters or monitor amps on smart overloads to actually "see" the motor is pulling current on the circuit. If I don't receive any positive feedback on this secondary means of detection, I send out an FALL alarm (FLOW ALARM LO-LO).
    Last edited by csc_wyo; 08-29-17 at 11:36 AM.

  3. #13
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    Quote Originally Posted by csc_wyo View Post
    You're spot on with your entire post and I do very similar things. However, I've learned a critical lesson before with a simple assumption. If you're truly looking for a fail safe solution, sending a command to a fan starter isn't exactly positive confirmation that your fan is running. Snapped/worn drive belts, spun couplings, local disconnects left open, HOA's in the OFF position or AUTO not proven are many ways to defeat that philosophy. I'm sure there are other codes, regs, guidelines that also specify a similar requirement, but NFPA 820 is very clear on what is required for positive detection. The last version I have is 2008, but in section 7.5.1, it sates that, "All continuous ventilation systems shall be fitted with flow detection devices connected to alarm signalling systems to indicate ventilation system failure." The cheapest and easiest way I've found to meet this requirement (in all industries I've engineered, not just wastewater) is to install a load side CT and relay on traditional starters or monitor amps on smart overloads to actually "see" the motor is pulling current on the circuit. If I don't receive any positive feedback on this secondary means of detection, I send out an FALL alarm (FLOW ALARM LO-LO).
    I don't see how CT monitoring proves there is any air flow. I think an air flow switch would be the appropriate solution.
    Bob

  4. #14
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    Quote Originally Posted by csc_wyo View Post
    You're spot on with your entire post and I do very similar things. However, I've learned a critical lesson before with a simple assumption. If you're truly looking for a fail safe solution, sending a command to a fan starter isn't exactly positive confirmation that your fan is running. Snapped/worn drive belts, spun couplings, local disconnects left open, HOA's in the OFF position or AUTO not proven are many ways to defeat that philosophy. I'm sure there are other codes, regs, guidelines that also specify a similar requirement, but NFPA 820 is very clear on what is required for positive detection. The last version I have is 2008, but in section 7.5.1, it sates that, "All continuous ventilation systems shall be fitted with flow detection devices connected to alarm signalling systems to indicate ventilation system failure." The cheapest and easiest way I've found to meet this requirement (in all industries I've engineered, not just wastewater) is to install a load side CT and relay on traditional starters or monitor amps on smart overloads to actually "see" the motor is pulling current on the circuit. If I don't receive any positive feedback on this secondary means of detection, I send out an FALL alarm (FLOW ALARM LO-LO).
    Thanks, that's good information. I agree as well on the air flow switch. Is anyone aware of a CID1 air flow switch? I noticed also that the requirement you listed is for continuous ventilation, which is not the scenario we utilize. Thoughts?

  5. #15
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    [QUOTE=rbalex;1853555]Just curious which Subsection of 500.7(K) [(K)(l), (K)(2), or (K)(3)] do you believe your design "... satisfies the intent of the NEC and RP-500 ...". Note those are the only acceptable NEC designs.

    I was reading through 500.7(K) (1) yesterday for another reason, and it made me think back to this discussion.

    (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.

    It made me think of another approach of classifying out analyzer rooms. We would install them the same, but rate them CID1 but install CID2 equipment based on this code section. I again find it interesting that gas detection is key, but they don't list what it should do, but I assume send a signal. In our case it would continue to enable the exhaust fan and strobes. Our fans are rated CID1 as well as the gas detection.

    I really appreciate this forum and how it spurs me to get into the code more and especially I appreciate the thoughts and feedback from others.

  6. #16
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    API RP500C

    Quote Originally Posted by petersonra View Post
    I don't see how this is a safe means of dealing with the problem. If the gas detectors see gas levels rising, it seems to me like it has become a C1D1 area. What prevents an explosion at that point since leaks tend to cause gas levels to go up very quickly, quite possibly before someone can respond. But then I have never really understood how the gas detection protection method is supposed to work since I have not had to use it in the past, so never looked at it real closely.
    SHORT STORY: Without all the drama and without if's, and 's of But's:-
    C1D1-Gases or vapors are ignitable under normal operating conditions in an area where OSHA rules expect employers to offer protection of life
    C1D2-Gases or vapors may be present but are normally confined within closed systems are prevented from accumulating by adequate ventilation (either mechanical or natural)

    Two basic fundamental curves to get you in the ballpark:
    Prevention of asphyxiant gas accumulation in concentrations that lessen the oxygen content to below the normal 21%.

    Prevention of ignitable concentrations between lower flammable limit (LFL) and upper flammable limit (UFL) so either not enough radical vapors to sustain a flame or too rich to catch on fire.

    Central compression plants leak vapors of carcinogenic (benzene) that are equally bad for your health and have long term effects on your survival. So equally important is that the redistribution of concentrated vapors do not then become the perfect explosive atmosphere when diluting with ventilation in an environment rich gas environment. Better read the entire API RP 500 C and move the (SPARK GENERATOR) further away from the leaking process.

    Problem solved. Just have engineering controls and work permits where only qualified escorted workers are allowed with belt gas detectors worn at all times and calibrated for the specific gas that may render you unconscious and then limit tools cameras and flash bulbs in the vicinity of the personnel working in the area.

  7. #17
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    API RP 500 C partial clarification

    6.3.2.4,4 Recirculation of inside air is permitted if:
    a. The recirculated air is monitored continuously with a gas
    detection system meeting the requirements of Section 6.5.2a
    through i, and, ---b. The gas detection system is designed to automatically stop“recirculation, provide an alarm (audible or visual, or both, asmost appropriate for the area), and provide exhaust (at a mm-.Note 1: Equation 1 applies when 7 >7’,. If 7’. < T,, replace T, with T, andimum rate as described in Section 6.32.4.2) to the outside if ,eplacc 7 withY,.vapor-air iiiixtures in concentration over 20 percent of their 2 The free area (A) determined in Equation I assumes that the free areaOwer amma e flint are ec . of the inlet is equal to the free ama of the outlet, lithe areas are not equal, usethe smaller of the iwo areas and refer to Figure 7. Chapter 22. of the 1935ASHRAE Handbook of Fundamentals, reproduced below as Figure). Thearea of the openings IA) as determined from Equation I esn be reduced bythe same percentage as the “increa.sc in percent” obtained from Figure I.Note: Sufficient dilution ate must be added to the space in question to ensurethat the concentration of flammable gas or vapor is maintained below 25 percent of the lower flammable limit (LFL) for all but abnormal conditions.

  8. #18
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    A lot of great information in this post that has helped me a lot.

    I would like to implement ventilation inside of an enclosure to ensure that it is Class I Div 2. Without ventilation, flammable materials could build up inside the enclosure making it Class I Div 1, with ventilation I feel that it is considered to be Class I Div 2.

    I purchased NFPA 30, and it is very helpful, but I was hoping it gave better details on implementing the ventilation system. NFPA 30 talks about ventilation systems for storage containers, and also goes into very helpful information for dispense station locations, but not for the equipment in the dispense locations.

    For the cabinet ventilation, I would like to use an explosion proof enclosure ventilation fan, and partner that with an explosion proof air flow sensor. The air flow sensor will allow me to detect a failure in the ventilation system.

    Is there anything else I would need for the enclosure ventilation system? Is there another standard out there that would help me implement the enclosure ventilation system? I believe the API RP 500 standard would be great, but I do not necessarily think a gas monitor system is absolutely necessary for this application in the enclosure anyway.

    I believe as long as the facility is following the requirements of NFPA 30 for dispense locations, then equipment will work very well in that location. Of course once the enclosure ventilation system is in place, all the rest of the installation inside the enclosure will have to comply with a Class I Div 2 location.
    Time is of the essence, and I am low on essence. ~ Graham Hill

  9. #19
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    Quote Originally Posted by petersonra View Post
    I don't see how CT monitoring proves there is any air flow. I think an air flow switch would be the appropriate solution.
    It's not perfect, but this is how I make it work. I run either E1 or E3 smart overload relays on all my starters. I do this for many other process, maintenance, and monitoring reasons, not just for this. However, during startup, I measure the current with the belt or coupling on the fan blade (baseline) and then with it off/de-coupled. I can then monitor the load through the E1/3 for a belt that's broke or an issue with the coupling. As stated in a comment below, finding a C1D1 flow switch, let alone finding an acceptable installation of one (size/location/raceway routing/environment ratings), is difficult. All AJH's I've had inspect the current monitoring installations have approved this as an acceptable way for positive detection.

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