Opening Purged Panels in Class I Div 2 area

[THansen]

Hi all -

Seeing if any of you have encountered this type of operational need before. We have a chemical process pilot plant that is classified as C1D2 due to presence of H2 and CO in the system at high temp and pressure. There are several electrical panels that are within the boundary of the C1D2 area for I/O and DCS system. All panels are purged. However, the facility has been encountering significant issues with fuse and card failure for which troubleshooting and replacement requires opening the purged panel. There is a consideration for working on the panels (which requires opening them, obviously) while system is operational and panels are energized to allow for troubleshooting. Interpretations have ranged from 'no way this is ok' to 'using gas monitors and hot work permit process for temporary work is ok'.

Anyone have experience in this type of operation or thoughts?

 

[rbalex]

I am personally of the "no way is this ok" school even though this is a Type Z scheme - but only because there is currently no method in either NEC Section 500.7(K) or NFPA 496 that would recognize using a gas detection scheme this way. I'm not a fan of gas detection anyway except to set the boundaries between potential fuel and ignition sources.

There is some ambiguity in NFPA 496: Section 4.11.2(1) seems to indicate gas detection may be acceptable but Section 5.3.1 would appear to prohibit power from being "restored"; i.e., it's already off.

That said, since this is a Type Z (Division 2 to unclassified) scheme, under "engineering supervision" with a well defined work plan AND a well documented set of identified fuel sources AND clearly defined temporary boundaries, I might be persuaded to allow a gas detection/hot work permit operation IF the hot work permit were signed off by the highest level of facility management. Sign off by the highest level of management won't make it safe of course, but they may think the better of a proper shut down.

 

[petersonra]

I am inclined to agree with Bob A. Not that my agreement means all that much.

I don't like the idea that somehow you can temporarily do something that you can't do on an ongoing basis.

It might be possible to take some additional precautions that would temporarily eliminate the need for the area to be classified but often that might well mean you would have to shut down production.

 

[THansen]

Thanks for the input! I think we are coming to a consensus to review each panel location and potentially allow very brief access for low voltage only (24v or less / mA signal wire) quick troubleshooting and IO card replacement only for those panels furthest from the hazardous areas, and requiring panels to be de-energized (or process not running) for anything above that. We are also looking at means to temporarily increase purge flows in the area, which seems acceptable. I do appreciate the input as a new member looking at these not so defined gray areas.

 

[rbalex]

Thanks for the input! I think we are coming to a consensus to review each panel location and potentially allow very brief access for low voltage only (24v or less / mA signal wire) quick troubleshooting and IO card replacement only for those panels furthest from the hazardous areas, and requiring panels to be de-energized (or process not running) for anything above that. We are also looking at means to temporarily increase purge flows in the area, which seems acceptable. I do appreciate the input as a new member looking at these not so defined gray areas.

This sounds a bit like wishful thinking. Besides NFPA 496, you should also familiarize yourself with NFPA 497. It may surprise you how little energy is necessary to ignite a flammable atmosphere. [See NFPA 497, Annex A, Section A.3.3.5.1] I'm not sure what you believe increasing the purge rate would do either.

Several of the protection techniques listed in NEC Section 500.7 are passive; not so with either purged/pressurized or gas detection systems. Trying to apply either of them in other than their proscribed methods is NOT recommended.

 

[petersonra]

It is non-trivial, but you might be able to just build a control room around the panels that can be itself pressurized but so that a person can get in and out. control rooms are often made this way. it is not trivial though.

maybe you can find a place fairly close by that is not classified to move the cabinets to.

 

[rbalex]

Philosophically, this is basically the same condition as an energized electrical work permit. As a matter of fact, you may need one of those too.

In either case, where operations management is reluctant to shut down for maintenance, the system wasn't designed properly in the first place. What is often overlooked is safety and reliability usually go hand-in-hand. Redundant equipment that allow a means to shutdown certain equipment for maintenance AND permit continued operations can be designed to permit both safe and reliable systems. Where management doesn't want to pay for it up front means they aren't actually interested in either safety or reliability or they're willing to accept unplanned failures.

BTW Bob P, I do appreciate both you opinions and suggested solutions.

 

[don_resqcapt19]

Bob,
I know we have talked about this issue a number of times and you have been very patient with me on the issue. This one is somewhat different. Here we have CO with an LEL of 125,000 ppm and an 10 minute exposure limit of 1,500 ppm. If that was the only flammable product, I would have no issues opening the panel in the classified area, because if I am still able to open the panel and I am not using supplied air, the atmosphere is no where near LEL.

The H2 is different as there are no specific exposure limits for hydrogen, but, as I was taught in my HazMat classes, because of the flammability of the product, you would consider a concentration of 10% of the LEL to be IDLH. The MIE of hydrogen is very low, and I think you would have to look at static free clothing and footwear to even enter the are if there is any chance you are even close to LEL.

Again, you have explained to me how the rules for area classification and life safety are independent from each other, I still don't see it that way.

Even here with the H2 atmosphere, if it has been deemed safe for me to be in the area, I don't see a significant reduction in that safety if I open the panel.

 

[GoldDigger]

Bob,
I know we have talked about this issue a number of times and you have been very patient with me on the issue. This one is somewhat different. Here we have CO with an LEL of 125,000 ppm and an 10 minute exposure limit of 1,500 ppm. If that was the only flammable product, I would have no issues opening the panel in the classified area, because if I am still able to open the panel and I am not using supplied air, the atmosphere is no where near LEL.

The H2 is different as there are no specific exposure limits for hydrogen, but, as I was taught in my HazMat classes, because of the flammability of the product, you would consider a concentration of 10% of the LEL to be IDLH. The MIE of hydrogen is very low, and I think you would have to look at static free clothing and footwear to even enter the are if there is any chance you are even close to LEL.

Again, you have explained to me how the rules for area classification and life safety are independent from each other, I still don't see it that way.

Even here with the H2 atmosphere, if it has been deemed safe for me to be in the area, I don't see a significant reduction in that safety if I open the panel.

Well, one factor to consider is that as far as life safety for breathing goes any concentration of hydrogen up to the point where the oxygen concentration is reduced from the nominal 20% to about 10% would still be breathable. Just similar to high altitude.

I would also worry about what happens to the rest of the conduit system when the positive purge pressure in the system is lost from opening the panels. There might not be an immediate rise in the H₂ concentration in the panel where you are standing, but H₂ might enter some other part of the system and cause a problem later.

Just free associating on the subject.

 

[rbalex]

Bob,
I know we have talked about this issue a number of times and you have been very patient with me on the issue. This one is somewhat different. Here we have CO with an LEL of 125,000 ppm and an 10 minute exposure limit of 1,500 ppm. If that was the only flammable product, I would have no issues opening the panel in the classified area, because if I am still able to open the panel and I am not using supplied air, the atmosphere is no where near LEL.

The H2 is different as there are no specific exposure limits for hydrogen, but, as I was taught in my HazMat classes, because of the flammability of the product, you would consider a concentration of 10% of the LEL to be IDLH. The MIE of hydrogen is very low, and I think you would have to look at static free clothing and footwear to even enter the are if there is any chance you are even close to LEL.

Again, you have explained to me how the rules for area classification and life safety are independent from each other, I still don't see it that way.

Even here with the H2 atmosphere, if it has been deemed safe for me to be in the area, I don't see a significant reduction in that safety if I open the panel.

Well, we're discussing Division 2 here so toxicity isn't supposed to be an issue anyway. I've attempted to dissuade the proposed activity in the first place since there's no recognized technique to deal with it. However, I've also attempted to outline a reasonable approach consistent with general safety practices.

When hydrogen "leaks" it spreads in ignitable concentrations very quickly which is why gas detection is generally useless. If the source is shut down quickly enough it does have the good grace to dissipate quickly. API has done several studies and any significant flammable leak (virtually any Class I flammable product with a flash point below 100?F) will almost certainly ignite no matter what the cause of the leak or cause of ignition.

 

[don_resqcapt19]

Well, we're discussing Division 2 here so toxicity isn't supposed to be an issue anyway. I've attempted to dissuade the proposed activity in the first place since there's no recognized technique to deal with it. However, I've also attempted to outline a reasonable approach consistent with general safety practices.

If we are talking about CO, and if we are looking at the possibility of an ignition caused by work being done on the electrical equipment, we have to be looking at the toxicity....a concentration of 10% of LEL is fatal in 1 to 3 minutes unless you are using supplied air.

This is a perfect example of my whole issue with just looking at the possibility of an electrical arc caused by doing work in the equipment as the major hazard, where, in this case, you would be dead long before you had an ignitable concentration of the flammable gas.

When hydrogen "leaks" it spreads in ignitable concentrations very quickly which is why gas detection is generally useless. If the source is shut down quickly enough it does have the good grace to dissipate quickly. API has done several studies and any significant flammable leak (virtually any Class I flammable product with a flash point below 100?F) will almost certainly ignite no matter what the cause of the leak or cause of ignition.

The possibility of igniting the hydrogen is a much bigger issue if you open the panel, but again with the very low MIE of hydrogen, should anyone even be in the area unless steps have been taken to prevent the workers clothing and or shoes from creating a static spark? The energy of the static spark would far exceed the MIE of the hydrogen if there would be a leak at they time a person is walking through the area.

 

[rbalex]

Don,

I have always understood your concerns; I have never said they weren't valid. However, as it currently stands, Section 500.1 is the only Scope of electrical area classification, installations in them and, to a lesser degree, operations. But it makes no mention of toxicity. Other than various "products of combustion" comments sprinkled throughout (none in Chapter 5), the rest of the NEC makes no serious mention of toxicity either.

I have also said, "If you want to use my electrical area classification documents for something other than selecting electrical equipment and installations, fine - but don't ask me to alter the documentation when you find the results are inconvenient for you purposes." I've had clients or other disciplines want it changed so they can use it for selecting fireproofing, roadway barriers, anti-sparking mechanical equipment such as overhead cranes, etc. In most cases they already had a valid basis for making the selections, but wanted my electrical area classification altered to "justify" it.

Make a "Public Input" comment for a new Informational Note to Section 500.1 to the effect that most classified materials are also toxic in concentrations below their flammability.