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Explosion proof
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(Electrical)
(OP)
15 Mar 19 14:06Sorry for what's probably a rookie question, but I just started this new contract and I have to get up to speed on this quickly. I need to understand the difference between Explosion Proof, Intrinsically Safe, Class 1 Div 1, and Class 2 Div 2. Let's say I have to specify some Control Valves for a customer, how do I know if they must be Explosion Proof etc? Is this something the customer must tell me? Let's say they are going in an area where I think there is combustible dust, do I specify Explosion Proof valves just to be safe? Thanks in advance for any help or advice!
(Electrical)
15 Mar 19 17:00First read the NEC (National Electrical Code).
An intrinsically safe device is a low power device that is certified to not use enough energy to cause ignition of the specified atmosphere. (See NEC)
An explosion proof device is certified to not release enough hot gasses to cause ignition of the specified atmosphere. (See NEC)
Gases may be released as a result of an internal explosion but will be cooled by passage between thermal masses so that any gases exiting will be below the ignition temperature of the specified atmosphere. (See NEC)
The power to and in an intrinsically circuit and device is not adequate to cause ignition of the specified atmosphere.
An explosion proof device contains and or cools hot gases below the ignition point of the specified atmosphere.
An intrinsically safe device will generally not have enough power to operate a valve.
There are divisions and subdivisions of hazardous atmospheres in the NEC.
Classification depends on the ignition temperature of the specified atmosphere, the probability of exposure to a hazardous atmosphere, the type of conductive and/or combustible dust or flyings. (See NEC)
An explosion proof device will be approved for specific conditions and/or atmospheres. (See NEC)
See the NEC
.
Bill
--------------------
"Why not the best?"
Jimmy Carter
(Electrical)
15 Mar 19 17:16Depends on area to include as explosion proof. If in USA, I would look at NFPA articles that include your industry. Some industries have particular NFPA standards. We dont know if your in heat treating, petro, or some form of chemical mixture like injection molding? Ask your employer do they have all the standards that cover their industry on hand? If they don't I would be worried what they did in past. In that case just stick it to them and order all the standards thru purchasing, your just a contractor.google is your friend!
(Electrical)
15 Mar 19 21:29There may be a few alternatives to both intrinsic-safety and explosion proof that might work for you. A common one for something like a valve would be to use a pneumatic valve, or a hydraulic valve, both of which avoid supplying ignition sources.A third is using a purged system that keeps the electrical apparatus at a positive pressure so hazardous materials can not get into the electrical stuff to be ignited. They take a supply of gas and pressure sensors that remotely disconnect all power if positive pressure is lost.
Keith Cress
kcress - http://www.flaminsystems.com
If you are looking for more details, kindly visit explosion proof electrical.
(Electrical)
15 Mar 19 21:49One other thing. You are wise to recognize a hazardous atmosphere and to seek aid with it. Especially hazardous dust. There are more people killed from dust explosions than gas, possibly because dust is harder to believe to be a hazard.I'd advise you get a practiced hazop person to check your solution because you are inheriting a lot of liability doing anything in this realm. I got deep into it doing a specific job with a company I worked at. We controlled sterilizer chambers the size of semi-trailers filled with the second most flammable gas that was also a strong carcinogen. Luckily I had a lot of experienced engineers with hazardous atmosphere experience to teach me and point out critical details I'd not thought of. Still customers regularly blew their buildings and equipment up but at least it wasn't because of anything I did.Keith Cresskcress - http://www.flaminsystems.com
(Industrial)
16 Mar 19 18:15Keith, sounds like ETO to me. Didja ever see the Chemical Safety Board's video on the Sterigenics explosion (out your way in CA) that blew the sterilizer chamber doors off? Supervisor provided password to bypass the standard multistage purge cycles.I had to commission steam flow meters in the El Paso plant (heavy ETO user, too) not long after the California episode and worried the whole time that someone would make a miatake (or more typically, a series of mistakes).
(Industrial)
16 Mar 19 18:28> Is this something the customer must tell me?
Yes, but it's up to you to ask and not to assume or leave unquestioned. It's standard question to a customer, "Does this _____ go into a hazardous area? If so, what area classification?"
The chunks of metal and plastic that valves are made of aren't the issue, it's the arcing/sparking ignition source that positioner/I/P electronics, limit switches, feedback signals or the electrical energy in an electrical solenoid or motorized actuator pose. For I/S, there's the potential heat source of ignition factor to consider as well.
(Electrical)
(OP)
16 Mar 19 20:36Thanks everyone for your help!
(Electrical)
16 Mar 19 21:00Hi Dan! Yes, I had pictures of it handed to me that my boss took in person of the results of that fiasco! The flame path of the explosion shot down the exhaust duct getting to the entire facility and screwing the entire place over. It collapsed the roof even. If I recall correctly they opened the door before a completed purge and started to drive a forklift up to it. The chamber atmosphere ignited blowing the door open so hard it threw the forklift and driver back to where they came from with the forklift landing on its side. Both workers were badly injured.El Paso! I spent a couple of days there entirely replacing their ETO sterilizer controller with ours. It was a pretty nice facility. I went thru all their stuff replacing a lot of it. It was an intrinsic-safety design. In the midst of the process I discovered they'd run ALL of their I.S. wiring thru a big wire duct shared with 480VAC power. I had to spend some time solving that mess.Keith Cresskcress - http://www.flaminsystems.com
(Electrical)
17 Mar 19 07:38Dan; I finally had a chance to watch that CSB report and I mixed up two different disasters. The Sterigenics one is the one my boss took pictures of. The fork lift one was at a different plant I had to go to to help out with. That plant wasn't destroyed because there was no explosion. The workers forced open the door while the chamber was under pressure. I believe it was a 12/88 facility - non explosive because of the 12%/88% mixture.Keith Cresskcress - http://www.flaminsystems.com
(Electrical)
7 Apr 19 17:44The first thing you need is the customer's "Area Classification" drawing - occasionally called a "Control Drawing" There will be one - NEC 500.4.A. What ever the area is classified, the equipment must meet that spec.Quote (PawSoxRule (Electrical) )
... how do I know if they must be Explosion Proof etc? Is this something the customer must tell me? ...
As mentioned, NEC Art 500.5, 500.6, Hazardous (Classified) Locations discusses Class I, Class II, Div 1, Div 2. Intrinsically safe, non-incentive, Purged and pressurized are described in 500.7. NFPA 496 discusses purged and pressurized. NEC 504 and NFPA 493 covers intrinsically safe.Quote (PawSoxRule (Electrical) )
... I need to understand the difference between Explosion Proof, Intrinsically Safe, Class 1 Div 1, and Class 2 Div 2. ...
Quote (PawSoxRule (Electrical) )
... do I specify Explosion Proof valves just to be safe? ...
The first thing you need is the customer's "Area Classification" drawing - occasionally called a "Control Drawing" There will be one - NEC 500.4.A. What ever the area is classified, the equipment must meet that spec.If you get unlucky, the drawings will reference NEC 504, Zone 0, 1, 2. There still has to be a drawing - NEC 505.4.A. Although that only references industrial occupancies.Uhhhhh .......... They don't have any drawings. Then that is your first task. There is a list of applicable standards in NEC 500.4. Most useful to me have been API RP 500, NFPA 30, NFPA 497. I have done little with Class II, so I can't help there. And API RP 505 for zones.As mentioned, NEC Art 500.5, 500.6, Hazardous (Classified) Locations discusses Class I, Class II, Div 1, Div 2. Intrinsically safe, non-incentive, Purged and pressurized are described in 500.7. NFPA 496 discusses purged and pressurized. NEC 504 and NFPA 493 covers intrinsically safe.No - you figure it out, nobody wants to pay for or have to work on explosion proof gear unless they have to. As said earlier, if they don't have an Area Classification drawing, then you get to make one - if only just covering your area of work.An un-asked aside: You are doing engineering for hire. Definitely get your Area Classification drawings stamped.As already covered, the subject is complex, requires lots of judgment. Getting (hiring) experienced help is a good choice.the wormHarmless flakes working together can unleash an avalanche of destruction
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These organizations have a (relatively) uniform approach when it comes to actually classifying equipment for use in hazardous areas. Through rigorous testing, a piece of equipment is assigned an area classification, division or zone, equipment group, and temperature class. An example of a Class I area would be an oil refinery, paint shop, or offshore oil rig. A Class II might be a coal mine, grain silo or hay storage facility. Class III would be something like a paper mill, textile mill, or woodworking facility.
Furthermore, a division or zone is assigned to the product. This is a description of the frequency with which the combustible gas and/or dust is present within the hazardous area. Divisions were used in older North American hazardous area standards, while zones are used in European/International standards as well as newer North American Standards.
The newer standards have switched to the use of zones, in part because they break down areas that previously were only described by two divisions into three more precise zones. Zones also have the added benefit of including the area classification with the zone description. Zone 0 describes an area in which a combustible gas will be present continuously while zone 20 describes an area in which combustible dust will be present continuously (the '2' in 'zone 20' indicates dust as opposed to gas).
The equipment group describes the type of hazardous material that is or could be present in the hazardous area. North American and international organizations use different standards to represent the equipment group, but they all describe the same thing: the type of combustible material in the presence of which the equipment can be operated.
Lastly, a device meant for use in a hazardous area is assigned a temperature class. The temperature class is the maximum ambient surface temperature the device can reach (under maximum dust layers where applicable). This rating is given to help prevent combustion based on the combustion point of the material present in the area. This is used to determine the ambient operating temperature of the device. The approved product will also have a maximum ambient operating temperature. Most facilities will want to operate at a maximum of 80% or below of the maximum ambient operating temperature. Some examples of temperature ratings commonly seen on devices are T1 (450°C), T3 (200°C), T4 (135°C), and T6 (85°C). Traditional US and Canadian systems may also include such temperature classes as T2A, T2B, T3C, etc., which indicate more precise temperature ratings.
As mentioned previously, there are several methods by which devices can prevent explosions in hazardous areas. First, an explosion-proof, flame-proof, or powder-filled device is one in which the explosion is contained and extinguished. Second, limiting the energy of the device to a point where combustion becomes impossible even in the presence of a flammable material, effectively removing the ignition source, is known as intrinsically safe or nonincendive. A non-incendive device prevents ignition under normal conditions. An intrinsically safe device prevents ignition in doublefault conditions. Lastly, a device can simply keep the flammable materials out of the electrical or heat producing components through pressurization, encapsulation, oil emersion, fiber and flying protection, or protection by enclosure. The particular protection concept that a device uses is represented by a marking on the device such as AEXd (Flameproof C1 Z1), Ex ia (I.S. CI Z0). These markings can be looked up on tables and charts available online from the various hazardous area approval agencies.
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