Motor selection for simultaneous C1D1 gr C&D plus div 2 hydrogen?

[Spaz]

We are having a discussion at work for an upcoming installation. Your input is approciated and hopefully will speed up our code interpretations...

We have equipment with a motor, XP disconnect for the motor, XP light, and other IS instrumentation already present . The equipment and area is rated for Class 1, Div 1, group D service (solvent vapors from loading/unloading containers).

We also now plan to simlutaneously use hydrogen in the same equipment. The hydrogen will be contained in the vessel for all processing (i.e so if hydrogen and not solvents was present, it would be rated Div 2 group B within 15 ft outside the "source" vessel). Everything within the NFPA defined area of 15 ft has already been upgraded (whether necessary or not) to Class 1, Div 1, groups B, C, D rating. Everything, except the motors, of course.

I already understand for C1D2 group B service alone that TEFC motors would be fine, and we already have all XP group C&D motors within 15 ft due to the solvents. But it is being discussed that possibly since the area is already Div 1 for group C&D, then it must be div 1 for hydrogen too, even if the hydrogen process is div 2 by definition. We'd loathe to spend 5-10 times an XP motor cost for purged XP motors rated B, C, and D (and that's how much they are).

What do you think about keeping the XP group C&D motors as they are (which would be fine in the separate cases of Div 1 for group D and Div 2 for group B)? Or should Div 1 be applied for all groups B, C, D, even if the group B process is Div 2 by definition?

 

[rbalex]

When questions like this come up, I often tend to question how the area was classified in the first place.

It is quite reasonable to infer that, if the process will produce Division 1 for Groups C and D, it will also create Division 1 for Group B; although probably smaller. Conversely, if the Group B is properly classified Division 2 only, the Groups C and D are also probably Division 2 only. But, since I don’t know the process involved, I can’t say.

Assuming though, that the location is indeed properly classified, the Division 1, Groups C and D motors are acceptable in Division 2, Group B.

 

[Spaz]

Thanks for the reply, I'll be more specific on the rating and process.

The group C&D rating is Div 1 in nature. comes from loading solvents from drums and totes, cleaning the equipment with solvents, etc. While it is likely that a div 1 condition or over 25% would never exist (especially since there is 12-15 air changes an hour in the plant), we have gone the safe route and classified Div 1 since we do use drums and totes. Considering the nature of the plant, operators, and procedures, the group C&D compounds are not treated with enough of "containment" strategy to justify a downgrade to Div 2.

The group B operation is Div 2. It is hydrogen and is very well contained and controlled, and the equipment is pressure tested twice prior to the batch and all flanges checked with a portable hydrogen detector when charged. There is zero tolerance for hydrogen leakage. The hydrogen is coming from cylinders, and is gas only. It is a textbook group B div 2 operation.

Our plant has performed this group B operation for 10 years now in older div 1 C&D plants, and there has never been any recorded incidents, and the hydrogen monitor has never activated except when using 25% LEL calibration gas. So there is much plant experience and my "trust" factor is very high. Regardless, any decision on this new plant would be retrofitted to existing equipment.

So what do you think of rating the room div 1 for C&D, but div 2 for group B hydrogen? While I think this is the solution, I can find no precedent for a "dual" rating myself, but maybe someone has done this somewhere else?

 

[don_resqcapt19]

So what do you think of rating the room div 1 for C&D, but div 2 for group B hydrogen? While I think this is the solution, I can find no precedent for a "dual" rating myself, but maybe someone has done this somewhere else?

That may cause problems for the other equipment as the most common equipment is rated for Groups C&D and not for B. Even some types of seal fittings are only C&D. You may have to make a lot of other changes.
Don

 

[Spaz]

That may cause problems for the other equipment as the most common equipment is rated for Groups C&D and not for B. Even some types of seal fittings are only C&D. You may have to make a lot of other changes.
Don

All the other equipment is already rated B, C, D, just not the motors. Junction boxes, EYS seals, motor disconnects, etc - no problem. Instruments and other small devices are either IS for A, B, C, D or XP and A, B, C, D, rated. But as I said, the motors are the issue. If the div 2 hydrogen was isolated in a separate area (which is impossible for us...), there would be no problems and everyone here would tell me keep the XP group C&D motors. But since the area is rated div 1 C&D and there are open solvents present, this becomes a strange animal in terms of room classification.

So we still have C1D1 C&D (possibly open solvents), plus C1D2 group B (the hydrogen is contained to the nth degree). Anyone hydrogenating in the chemical industry for the last 50 years (100 years?) has the same situation, but group B XP motors haven't been available until a couple years ago, and really they were made for Div 1 hydrogen - typically people using liquid hydrogen like NASA and the sort. Hmmm.

 

[rbalex]

Having gone back and read both your OP and subsequent responses tends to confirm one of my suspicions – you probably over classified the Division 1, Group C and D areas. Nonetheless, there’s nothing wrong with doing that.

Technically, overall electrical area classification is an entire array of overlapping locations, each individually determined by the various sources involved. You really have at least two processes, one with the Group C and D materials and another with the hydrogen. It is entirely permissible to superimpose the individual area classifications on the same facility. The only restriction is that the same physical location cannot be classified by both “Divisions” and “Zones;” although an overall facility may use both systems. See Section 505.7(B)

If, as you have noted in the OP and responses to Don, the “other” equipment is already suitable for the Class, Division, Group, Temperature etc. as necessary and required by 500.8(A), then the motors meet the requirements of 501.105(B) for the Division 2, Group B location.

Your experience is also relevant. One of my favorite citations from NFPA 497(2004 Edition):

5.5.4 When classifying buildings, careful evaluation of prior experience with the same or similar installations should be made. It is not enough to identify only a potential source of the combustible material within the building and proceed immediately to defining the extent of either the Class I, Division 1 or Division 2; or Class I, Zone 1 or Zone 2 classified areas. Where experience indicates that a particular design concept is sound, a more hazardous classification for similar installations may not be justified. Furthermore, it is conceivable that an area be reclassified from either Class I, Division 1 to Class I Division 2, or from Class I, Division 2 to unclassified, or from Class I, Zone 1 to Class I, Zone 2, or from Class I, Zone 2 to unclassified, based on experience.

Edit underline added

 

[Spaz]

Technically, overall electrical area classification is an entire array of overlapping locations, each individually determined by the various sources involved.

Thanks very much. It is an especially eloquant(sp?) way of describing it. I was looking for some confirmation on my feelings on the Div1/div2 classification, and this helps.

Having gone back and read both your OP and subsequent responses tends to confirm one of my suspicions ? you probably over classified the Division 1, Group C and D areas. Nonetheless, there?s nothing wrong with doing that.

I agree with you on the overclassification of div 1, to me it's div 2. I would rather classifiy the area what it really is, then decide where we want to upgrade the safety, rather than go up a classification and have the code decide it for us. But I work here - I guess if i were consulting I might be more cautious if I don't intimately know the facility and procedures.

Again thanks, hopefully I can be of help to someone here in the future.