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Old January 6th, 2017, 01:55 PM   #1
SolarNinja
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PLC to replace spark detection/suppression system in LP ducting, good idea or bad?

I have been tasked with implementing a spark detection/spark suppression system in our low pressure (.9" w.c. 28" dia. round duct) main dust control trunk.

Our chief electrician (also a PLC guy, x military, super smart, installed and programmed automation systems in bottling plants, mills, processing facilities, etc.) and I decided that we would have a CompactLogix L32 be the heart of our spark detection system. This was about 6 months ago. We already have a hardware based system built in 1984 that has been refurbished by a reputable fire safety company, but it cannot monitor velocity. Since we are constantly changing our ducting and controlling flow manually with the use of dampeners I feel it is important to monitor velocity in our main trunk line. The reason it is important is that it takes time for the suppressors to actuate, so we need to make sure that sparks do not make it past the suppressors before water is applied. I am using the same spark sensors and suppression units supplied by the fire protection company, as well as their test lights and field data.

The system is VERY simple. In a nutshell (not explaining redundancy systems) there are two sensor banks, each with two spark sensors. Zone 1 and zone 2. Zone 1 detects a spark, then a downstream suppression unit energizes for a period of 5 seconds after the last spark is detected. If by some chance a spark makes it past the suppression unit into zone 2, zone 2 sensors will see the spark and actuate an "abort gate", which completely stops air flow immediately. SIMPLE.

This thread should be interesting. I was advised (by the manufacturer of the fire safety system) that I had to use their hardware. Well, licensing and code aside, what I am looking for is safety first, forget everything else. They failed to tell me WHY I cant use a PLC to detect spark. I mentioned something I said in another thread and a gentleman there said that I cannot use a PLC to run fire safety equipment, that there were dedicated systems for that. He asked others to chime in, so I started a new thread on the topic because I cannot afford to be making stupid mistakes here.

So far I have used the PLC to collect spark sensor data, and actuate the suppression units. No problem there. I am trying to visualize a circumstance where a PLC is not "safe"...a situation where the program will not protect against fire. Thus far, every single circumstance that I can foresee can be handled by redundancy programmed into the PLC.

(1) sensors faulting (prevented by periodic automatic sensor tests)
(2) PLC shut down (make an alarm happen if PLC faults)
(3) Suppression actuators not functioning (monthly actuator checks, this may not seem ideal, but that's the same way the dedicated fire safety system works...there is no way to "test" them without physically turning them on and making sure water is coming out)

...you get the picture. I can't see a damaging event or failure that cannot be solved by redundancy. The fire system that we have is rebuilt, so it should be operational and "safe", but I didn't build the thing, so I can't work on it. Plus, electronic components fail. PLC, if you adhere to the ISA-88 standard, can be worked on by any competent ladder logic programmer. True, years of R&D went into these fire safety systems, but you have to think, they make a **** ton of money on these systems, for something that performs a relatively simple task. If they switched to PLC systems (I can see why they would not want to do so) they wouldn't make NEARLY as much money. And money, my friend, is the whole reason they are in business. Code and licenses aside, I want something that WORKS, is PRACTICAL, and SERVICEABLE.

So far at least two people have told me that I cannot use a PLC for spark detection/suppression, however, no one has given me any reason why. The PLC seems far superior in every way than a bunch of hardware that can fail at any point just as easily as the PLC. That being said I very much welcome and value ANYTHING anyone has to say on the subject. Thank you so much for reading, and I am more than happy to post my experience these next few months detailing how this project unfolds.
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Old January 6th, 2017, 02:02 PM   #2
Christoff84
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Another point of view is from your insurance company. If you home brew a spark detection/suppression system and it fails, you may be on the hook for the damages.
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Old January 6th, 2017, 02:14 PM   #3
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an alarm may not be adequate if the PLC loses power or the program stops running. It should stop the process if it is unsafe to continue operating without the PLC.

What if someone changes the PLC program and inadvertently (or maliciously?) makes a mistake? You will need some way of proving the PLC program has not changed, and if it has then the program will need to be proved to operate correctly before the process can resume operation.
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Old January 6th, 2017, 02:16 PM   #4
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(4) Unintentional programming or wiring mistake made by inexperienced designer that doesn't crop up until the sh*t hits the fan and leads to said designer sitting in a laywers conference room (or God forbid the DA's office) somewhere giving a deposition about why exactly he, as a person unfamiliar with NFPA codes or even basic PLC wiring, felt he was qualified to design and implement a life saving fire suppression system.

Companies who make fire alarm and suppression control equipment charge a lot of money for many reasons, not the least of which because they carry some liability if something goes south with their equipment. They design and test it to standards you wouldn't believe. It's worth it, there isn't some conspiracy or cabal of manufacturers not using PLCs on purpose because it would drive costs down. They don't use PLCs because PLCs are the wrong tool for the job, period.
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Old January 6th, 2017, 04:06 PM   #5
Dravik
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Your bog standard PLC is not designed to be used as an integral part of a safety system. They aren't setup or designed with that function in mind.

You *could* use a Safety rated PLC, with Safety inputs/outputs, and design the system to meet whatever SIL you need w/ all the proper rated components.

Do a risk analysis, get all parties on board, have someone sign off on whatever you do.

Here's a very light overview of the difference in PLC/Safety Plc http://literature.rockwellautomation...p002_-en-e.pdf

Quote:
Originally Posted by SolarNinja View Post
I have been tasked with implementing a spark detection/spark suppression system in our low pressure (.9" w.c. 28" dia. round duct) main dust control trunk.

*snip*

Last edited by Dravik; January 6th, 2017 at 04:13 PM.
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Old January 6th, 2017, 04:10 PM   #6
just the cowboy
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Insurance

When I work for a very large manufacturing plant we could build anything that involved manufacturing a product. BUT the only two things we could not touch were the fire systems and elevators. Yes I could have rebuilt an elevator control panel to replace our old one for 10% of what the Elevator Company wanted but corporate said no. We were so big we had a 50 million deductible but still the insurance co said no.

Stay away from it for liability reasons, our jobs come second to ourselves.
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Old January 6th, 2017, 04:46 PM   #7
SolarNinja
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Christoff84, I do not care about insurance or code, I care about safety. I am reasonably sure that I can get the system approved by the same outfit that approves the rest of our control enclosures.
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Old January 6th, 2017, 04:49 PM   #8
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VonHydro, thanks for your insight. Know that we have been running for over 2 years with this dust collection UNPROTECTED. If the system goes down and the alarm sounds we can have a redundancy in place that should the PLC lose power, the dust collector shuts off. In other words, an energized output is necessary to keep the dust collector functioning...so no chance of catastrophic failure there.
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Old January 6th, 2017, 04:51 PM   #9
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Thank you Dravik, I will take a look at that piece of literature. I believe the CompactLogix is loaded with safety features, (and motion control to boot!), but as I earlier mentioned, I just need it to work safely, and if it shuts off or faults for any reason, have the dust collector shut down.
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Old January 6th, 2017, 04:58 PM   #10
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Good insight bjh. I am confident in my PLC programming abilities, and that means including triple redundancy for any faults in wiring. There are only three pieces of equipment that need to function, sensors, suppressors, and abort gate...all of which will have periodic testing for functionality. Just a TWITCH of voltage drop in any ONE of the 4 spark sensors will open that suppression solenoid, and should that solenoid fail to function that abort gate will close and the dust collector will shut down. I have designed, built and programmed solar panel manufacturing cell stringing machines (look at them on YouTube) which are incredibly complicated. This system that I am building is a wrench compared to, well, compared to a delta table saw. I am 100% certain that I can build enough redundancy to prevent fire from reaching the dust collector's bag house.
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Old January 6th, 2017, 05:01 PM   #11
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JustTheCowboy, and everyone else for that matter, bring up some very good points. I will discuss everything that I learned from this thread with the owner and production manager so a thorough cost and risk assessment may be performed. I am hoping that we can make our own system and get it UL approved, but I feel like we may need to speak with an attorney who knows insurance so we don't get caught with our pants down should an incident occur. Thanks again for all of the great information! Looking forward to hearing more of what people have to say.
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Old January 6th, 2017, 05:09 PM   #12
James Mcquade
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SolarNinja,

You may not care about insurance or code, but let there be an incident regarding the equipment you put in and you will care !!

If your company is found at fault, they will be sued and you will be named as well in the lawsuit. When that is over, and if someone dies, the family members may sue you in a wrongful death lawsuit. Your career will be over !

unless specifically designed for that purpose and tested extensively by ul and other agencies, a plc will not meet the requirements for the suppression system.

if you install your own system and something goes wrong,
Your company insurance will be void (it says so in the policy) leaving the company to foot the bills, and you WILL be the scape goat.

Now then, to the question at hand.
All fire suppression systems are required to operate within a certain timeframe once a sensor is triggered.

I used to work in a class 1 div 1/2 and class 2 div 1/2 facility and everything
had to be inspected and tested by the manufacturer with the results going to the insurance company as well as others.

No rudeness intended, just cold hard facts!
I know from personal experience from others I know what will happen,
and you do not want to go there.

regards,
james
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Old January 6th, 2017, 05:18 PM   #13
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This is the Dunning-Kruger effect in action.

Quote:
This pattern of over-estimating competence was seen in studies of skills as diverse as reading comprehension, practicing medicine, operating a motor vehicle, and playing games such as chess or tennis. Dunning and Kruger proposed that, for a given skill, incompetent people will:

fail to recognize their own lack of skill
fail to recognize the extent of their inadequacy
fail to accurately gauge skill in others
recognize and acknowledge their own lack of skill only after they are exposed to training for that skill
And it's not a bad thing because EVERYONE does this, but you need to recognize that you may be a tad overconfident here. We saw in your other thread that you simply don't know what you don't know - and that's OK! As you learn more you'll also learn why everyone here is telling you not to do this. You're literally playing with fire and need recognize why it's a bad idea to "homebrew" this.
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Old January 6th, 2017, 05:41 PM   #14
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A UL label from a panel shop and an in-house electrical design might be fine from a functional and electrical point of view.

But the "code and insurance elements" are really the only parts that matter.

Your insurance carrier is going to want to know one thing: "Where's the Factory Mutual sticker ?".

An in-house system is not going to be acceptable to your insurer or to Washington Department of Labor & Industries unless it's either FM-approved or it's been subject to a rigorous review from a licensing authority based on at least these NFPA standards:

NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
NFPA 68: Standard on Explosion Protection from Deflagration Venting
NFPA 69: Standard on Explosion Protection Systems

The hardware used in fire suppression systems is relatively cheap; I'm always amazed when I see unprotected circuit boards in simple enclosures. The real money is in analysis, engineering, standards compliance and insurance.
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Old January 6th, 2017, 09:57 PM   #15
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Do some reading up on NFPA 654....it sometimes refers to the installation of "listed" systems, which you maybe using listed components, but not a "system".
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